WO2011012587A1

WO2011012587A1 - Process for the production of a core with integrated bridging fibers for panels made of composite materials, panel that is obtained and device

Info

Publication number: WO2011012587A1
Application number: PCT/EP2010/060824
Authority: WO
Inventors: Frédéric PINAN; Thierry KLÉTHY
Original assignee: Saertex Gmbh & Co. Kg; Saertex France Sas
Priority date: 2009-07-28
Filing date: 2010-07-26
Publication date: 2011-02-03

Abstract

The object of the invention is a process for the production of a core with integrated bridging fibers (12) for the manufacture of composite panels, comprising the steps of : providing a cake (10) made of light material of the rigid foam type, forming the core, depositing excess bridging fibers (12) on at least one surface (18, 20) of the cake (10), making a portion of these bridging fibers (12) partially or totally penetrate the cake (10), removing excess, unused bridging fibers (12). The invention also covers the panel that is obtained as well as the associated device for producing a core.

Description

PROCESS FOR THE PRODUCTION OF A CORE WITH INTEGRATED BRIDGING FIBERS FOR PANELS MADE OF COMPOSITE MATERIALS, PANEL THAT IS

OBTAINED AND DEVICE This invention relates to a process for the production of a core with integrated bridging fibers for the manufacture of composite panels.

The invention also covers the core that is obtained as well as a device for producing it, and a panel obtained from the core.

These panels consist in a known way of a core made of light foam-type material, core on both sides of which two skins are attached.

These skins are integral with each of the surfaces of the core. These are the skins that impart the mechanical properties to the panel because of the increase in the moment of inertia by spacing these two skins.

Each of the skins is made integral with the core. The industry is looking for composite material panels with improvised mechanical capacities by elimination of limiting actions of these properties produced by delamination and by the core breaking at its center.

It is therefore necessary to use compatible materials to implement this connection and to compensate for the poor mechanical properties of the core.

Actually, each skin is made from a mat of fibers immersed in a resin.

It is necessary to provide compatibility between the resin that is used as a matrix and said foam.

Nevertheless, the panels that are thus obtained have mechanical properties that are limited and that it is possible to enhance very significantly. Actually, under certain actions, in particular flexion, delamination of one of the skins by disengaging this skin from the core is noted. Actually, to increase the resistance to delamination and to take full advantage of the complete resistance of the panel, improvements have been conceived. It is thus known to create bridges between the two skins.

These bridges have been created by holes made in the core so that the resin flows through these holes during the creation of skins. Nevertheless, if this is an improvement, the enhancement of mechanical effects is inadequate.

As a result, the concept was developed of connecting the skins to the core by running fibers from at least one of the skins through the core either all the way through if one of the skins is involved or part-way or all the way through if the two skins are involved.

Thus, the resin can migrate along fibers that run part-way or all the way through and thus form bridges between the two skins that are thus, themselves, composite material bridges. The European Patent EP 1 686 210 describes a composite panel that thus comprises a core with two fibrous skins, whereby these fibrous skins are connected to the core by a solidified bonding material, and original bonding fibers from at least one of the skins have been embedded, in particular perpendicularly, in the separating volume between the skins and therefore in the core.

This document also describes a device that makes it possible to produce, continuously and simultaneously, a skin on each side of a core and to make a portion of the fibers of these skins penetrate through the core, all the way through or not, by needle-bonding. The French Patent Application FR 2 921 076 describes an improvement of the patent that is mentioned above.

This application provides that at least a portion of the embedded connecting fibers from at least one of the two skins has at least one oblique orientation relative to at least one of the two skins. Thus, the two skins are connected to one another by bridges that consist of fibers obtained from these two skins.

The drawback of such panels is the selection of fibers. Actually, it is understood that the fibers that constitute the skins are not necessarily suitable for another usage, namely the migration of resin and the "bridging" of skins.

Actually, the nature, the diameter, the length, and the type of fibers that constitute the skins do not generate adequate mechanical properties or a power of migration that is quick enough, to cite only the essential parameters.

Finally, not only the fibers are of a unique type but the needle-bonding can prove unsuitable when the thickness of each of the skins varies or the density. The combinations are therefore very limited.

There is a demand, however, for products with strong mechanical strength, and

requirements for high production speeds of the panels, although the migrating power of the resins should also be enhanced. The rates are important, but the diversity of requirements is also important, so that it would be advantageous to be able to use prepared cores, on the one hand, and skins prepared in advance or produced in situ, but thus allowing numerous combinations.

It is one object of this invention, among others, to propose a process for the production of a core that includes pre-connections, designed to accommodate at least one skin for forming a panel with high mechanical strength and with very high resistance to delamination.

The object of the invention is also a core that is thus obtained by the process and a panel that is produced from this core as well as the device for producing said core.

In a first aspect, this object is achieved by a process for the productionof a core with integrated bridging fibers for the manufacture of composite panels according to claim 1.

In a second aspect, this object is achieved by a core according to claim 8. In a third aspect, this object is achieved by a panel of composite material according to claim 11.

In a last aspect, this object is achieved by a device for the manufacture of a core according to claim 14.

Preferred embodiments are described in the dependent claims.

The invention is now described in detail according to a particular, non-limiting embodiment, with regard to the drawings that show:

Figures 1 A to 1 D a synoptic view illustrating the process that is implemented according to this invention for the manufacture of a core with thread reinforcement, Figures 2A and 2B three kinds of thread for making bridging fibers, Figures 3A to 3C a cutaway view three kinds of cores,

Figures 4A and 4B two views of two panels produced from a core that is obtained by the process, and

Figure 5 a schematic view of the device that makes it possible to produce the core according to this invention. The process according to this invention is described with regard to the block diagram of Figure 1. In stage A, this process consists in using a cake 10 made of light material, for example a rigid foam with a density in the range of 15 to 60 kg/m³, preferably between 25 and 40 kg/m³, which constitutes a core 11 (see Figure 1A). In preferred embodiments, the cake can be made of e.g. one or more materials of the group consisting of a polyurethan foam, a polyester foam, a polyethylene terephthalate foam, a polyvinyl chloride foam, and a phenolic foam. In a specific example, a polyurethan foam with a density of about 35 kg/m³ may be used as material for an elastic core or a polyester foam with a density of about 30 kg/m³ may be used as material for a rigid core. This light-material cake is, in a known way, a plate that is parallelepiped in shape and of several centimeters of height, to give a simple example. Preferred heights are in the range of 3 mm to 50 mm. Plate is defined as a monolithic plate or a reconstituted plate of mono-material or multi-materials. In particular, the cake 10 can be made of two or more materials. E.g. a core with a height of 20 mm may consist of a first layer of 10 mm of a polyurethan foam and a second layer of a polyethylene terephtalate foam. The core may be made of any other combinations of two, three, four or more layers of arbitrary heights and various materials.

During stage B, the cake 10 then receives at least one type of bridging fibers 12 on at least one surface 18, 20, in this case on the upper surface 18. These fibers 12 are deposited on the surface without any connecting element.

Hereinafter, "fiber" is equally called mono-filament fibers, multi-filament fibers or else threads. Various kinds of fibers e.g. are described in pending French patent application no. 09 55259, the content of which is hereby incorporated by reference. Hereinafter, reference is made to a single type of bridging fibers, but there can be different types of them at the same time.

These fibers 12 are obtained from, for example, a multiple cutting of continuous threads so as to generate fibers of suitable length. There are cutters that make it possible to manufacture these fiber sections in situ. Preferably, the fibers are made from bundles of filaments that are linked so that the cutting of the threads leaves the ends of filaments connected.

These fibers 12 are deposited on the surface in a quantity that is at least equal to the bridging requirements. The case being, these fibers are deposited in excess quantity.

These fibers are suitable for bridging and can be selected, for example, from among threads in the form of bundles of filaments of low grade, e.g. with a diameter of 4 to 30 μm, preferably 6 to 30 μm, or bundles that are threads of high grade of e.g. 20 to 10000 tex, preferably 30 to 10,000 tex.

Said filaments are connected so that the cutting of this thread leaves the ends of the filaments connected. The bridging thread can be produced by braiding said bundle of filaments using a connecting thread of the same nature or of a different nature from the material that constitutes the filaments of the bundle, with a winding in a helix, for example, of this connecting thread around said bundle.

This braided thread offers important advantages, in particular the one of monitoring the quantity of fibers that are inserted and the one of enhancing the migration of the resin during its use for the production of panels as will be explained below. In addition, such a braided thread allows the production of quality bridging threads.

A bridging thread 13 produced by braiding is illustrated in Figure 1. Braiding is an operation that consists in helically winding at least one thread onto the periphery of the bundle of filaments. This winding can be in a single helix or in a double helix with opposite winding directions.

According to a particularly satisfactory example, the bundle consists of glass or carbon filaments 15 that have high mechanical strength properties, with a braiding 14 that comprises at least one helical winding 16 by means of a thread made of thermoplastic polymer, such as polypropylene (PP) or polyester (PEs).

This thermoplastic thread is heated after winding so as to make it possible to reach the softening point that imparts to it a power of adhesion on the outside filaments of the bundle. The thus braided thread can be cut, whereby the filaments at the end are held in a bundle.

The added thermoplastic thread simultaneously contributes to limiting the weight and to associating an inexpensive material whose wettability coefficient is high. In this case, the resin can flow into such a thread in the direction of the filaments but also perpendicularly, thus facilitating penetration.

The parameters for adjusting compactness, mechanical strength and draining power of such a thread are:

Number of filaments

- Grade of filaments

Nature of filaments Number of braiding threads

Grade of the braiding thread or threads

- Span and winding tension of the sheathing thread or threads

Nature of the sheathing thread or threads.

In the case of a thread 13 that comprises a bundle of filaments 15 made of glass and at least one winding with a glass thread and connecting means by addition of a very small quantity of resin, a material homogeneity is preserved because the quantity of polymer is considered insignificant.

A second kind of thread 13 is illustrated in Figure 2, consisting in producing a partial sheathing 18.

A partial sheathing solution consists in arranging successive rings 20 on the periphery of the filaments 15.

This solution for production of this partial sheathing 18 consists in successively extruding thermoplastic polymer rings 21 in a way that is coaxial relative to the bundle. In the same way as above, it is possible to vary the compactness, the mechanical strength and the draining power of such a thread by modifying the following parameters:

Number of filaments

Grade of the filaments

Nature of the filaments

- Number of rings per unit of length of thread

Length and thickness of the rings

Shrinking power of thermoplastic polymer

Nature of thermoplastic polymer The rings can be replaced by at least one thermoplastic polymer helical sheathing in a way that is coaxial relative to the bundle.

A third of thread 13 is illustrated in Figure 2C and is produced by assembling the bundle of filaments 15 and immersing it in a matrix 22 by a total impregnation of a thermoplastic or thermosetting resin that is then polymerized. The filaments are made integral with one another, and the interfilament spaces are filled in with resin.

In this case, the thread 13 that is obtained can also be cut, the cut end remaining monolithic.

The mechanical strength of the thread is that of the filaments, and the thread is actually very homogeneous.

The constraint is to control the compatibility of the impregnation resin of the thread 10 with the resin of the final composite material that will integrate such a thread.

The thread 13 that is obtained according to the process for production can be cut into thread sections 13 and used in different ways in its same reinforcement and drainage role. In Figure 3A, a reinforcement 41 with two skins 40, 42, for example made of non-woven glass fibers, is shown.

Between these two skins, it is necessary to use a draining core 44, for example made of thermoplastic polymer threads or other light material. The reinforcment may be made form a core according to the present invention and the two skins 40, 42 by placing the skins on the core with the bridging fibers sticking out of its upper and/or lower surface such that theskins come to rest on the core.

Owing to the different nature of the two skins and the draining core, there are significant delamination risks of the final composite material part that is obtained. The mechanical strength remains average. The central zone is still a potential zone where rupture may start.

Also, the thread 13 cut in bridging fibers 12 may be used to produce links between the two skins 40, 42 by forming bridges 46. The thread sections can be introduced perpendicularly or at an angle as in Figure 3A.

The great advantage of such an arrangement is to greatly increase the mechanical properties by very greatly limiting the disruptions of the flow of the resin in the drainage layer. Figure 3B shows the advantage of a thread 13 as explained with respect or Figures 2A to 2C in the case of reinforcements 41 for so-called "sandwich" panels comprising a balsa or foam core 48, for example, with a skin 40, 42 on both sides. Such panels, to withstand forces in particular of flexion and torsion to which they are subjected, are to have an important inertia module. The latter is directly connected to the distance that separates the two skins.

In contrast, because of the irregularity of the materials and the fragility of the core, the latter is led to break.

Bridging fibers 12 that are inserted passing through the core 48 and forming bridges 46 ensure the connection of the two skins 40, 42 and the cohesion with the core 48. The resin that will impregnate the skins will also migrate into the bridging fibers 12, obtained as explained before.

During stage C, it is provided to make the bridging fibers 12 penetrate in a way that runs all the way or part-way through the cake 10 (see Figure 4C). A known and industrially acceptable means for the manufacture of such products is the needle-bonding.

The needle-bonding consists in having needles 31 penetrate through core 1 1. Each needle 31 comprises one profile end that is suitable for ensuring the entraining of the bridging fibers 12 in the direction that the needle is inserted and for removing the needle without entraining the fibers 12.

It is also provided that the fibers 12 penetrate part-way in the cake 10 or all the way through the cake 10, and therefore pass through it. The depth of penetration can be chosen depending on the mechanical characteristics to be obtained by panel made using the core 11. Furthermore, each fiber 12 can totally penetrate the cake such that it is over its whole length inside the cake, or preferably it can partially penetrate the cake such that it sticks out on one or both surfaces of the cake. These fibers 12 can be inserted perpendicularly relative to the plane that is constituted by the surfaces 18, 20 of the core 11 to which the bridging fibers 12 are connected, but these fibers can be inserted obliquely relative to this surface 18, whereby the angle can be positive or negative or a portion with a positive angle and another portion with a negative angle within the same core. The angle varies in particular and commonly between 45° and 90°. In particular, the bridging fibres 12 are inserted at one, two or more defined angles relative to the surfaces 18, 20 of the cake 10. E.g., a core can have bridging fibers 12 all being oriented with an angle of 90° and +45° and/or -45° relative to the surfaces 18, 20 of the core 11 , thus combining the mechanical properties of perpendicular and tilted bridges in a later panel.

The concept is that the bridging fibers can also be introduced according to a predetermined pattern.

Once a portion of the bridging fibers 12 is integrated in the cake 10, excess bridging fibers are removed, Figure 1 D.

A core 1 1 with visible bridging fibers on at least one surface and at least partially integrated within the core 1 1 is thus obtained. According to a variant, it is also possible to have the plate return to reach the second surface 20 that is oriented upward to deposit excess bridging fibers, as on the surface 18.

These fibers in turn are needle-bonded to be partially integrated within the thickness of the core 11 or to pass all the way through.

Once the fibers in question are needle-bonded, the non-needle-bonded excess is removed from the core. In this case, the fibers pass all the way through on two sides and are partially integrated in the two sides. In the same way, without any difference, the installations of the fibers, the needle-bondings and the removal of excess on each surface can be implemented simultaneously on the two surfaces. The fibers of the downward-oriented surface are then held temporarily during the needle-bonding by a veil, for example. In a same way, two cakes may be provided on one surface each with bridging fibers and then be put together to form one core with bridging fibers sticking out on an upward and on a downward surface. So as to simplify the following description, the example that is retained covers an embodiment according to which a core 1 1 is used with bridging fibers that completely pass through the core, obtained from each of the two surfaces and that are visible on the two surfaces 18 and 20 of the core 1 1 , see Figure 4B.

Nevertheless, another example with a layer of fibers on a single surface is shown in Figure 4A, whereby the bridging fibers 12 pass all the way through and are partially integrated in the core.

Likewise, a bridging thread of a single type is selected in this example.

The core 1 1 that is thus obtained, with integrated bridging fibers, is ready for the production of a panel 22.

Such a panel receives a layer of skin fibers 24 on each surface 18, 20.

According to a first embodiment, this layer of skin fibers 24 is manufactured in advance and deposited on each surface of the core 11 , the sandwich consisting of three layers then being placed in a mold within which the resin is infused by several inputs to allow a good distribution over the entire surface of the panel.

The mold is generally heating to ensure the polymerization of the resin more quickly. It is possible, of course, to use other techniques such as the one of fibers that are pre- impregnated with resin that should be brought to temperature to ensure good diffusion in a first step and polymerization in a second step.

The selection of the technique is not a crucial point and depends on applications under consideration and available material.

According to a second embodiment, the skin fibers 24 are deposited on the two surfaces and held in place by a veil that also ensures an excellent final surface state after removal from the mold. In the first or second variant, the projecting ends of the bridging fibers are taken up within the layer of skin fibers 24.

The resin in the two cases is distributed and migrates within skin fibers but also migrates within the bridging fibers that it also wets, thus producing fiber/resin composite bridges between the skin fibers of the two surfaces.

The skin fibers are selected based on mechanical effects, the surface condition to be obtained, the quality of migration of the resin while the bridging fibers are selected based on their capability of being needle-bonded, their mechanical strength, their capability of being cut, and their capability of allowing the proper migration of resin. Preferably, the skin fibers and the core are made of different materials. The skin and the cake material of the core may both be made of a thermosetting or thermoplastic polymer or of mono- or multifilaments of natural, mineral or synthetic fibers. In particular, the cake material may also be a foam. preferably a skin of a certain material is combined with a core of a different material. When using a skin on more than one side, the skins may be of different material each.

In the retained embodiment that was just described by way of example, a panel with a core, two skins, one on both sides of said core, and bridges between the two skins is obtained.

The thus obtained panel is particularly advantageous because it is totally optimized based on the application.

It is also noted that the manufacturing process according to this invention is advantageous in terms of management of cores because starting from the same type of core, the panel manufacturer can combine different types of fibers for the skin, and even combinations of different types of fibers.

These skin fibers can also undergo a surface needle-bonding only to the core, without any mechanical effect, while awaiting casting in resin and polymerization.

In this case, this needle-bonding does not have any bridging role but rather a "lacing" role.

To carry out the vertical needle-bonding of the bridging fibers on the core according to this invention, a device is provided that comprises (see Figure 5):

- A station 26 for supply of light-material cake 10, a station 28 for deposition of bridging fibers on each cake,

a needle-bonding station 30,

a station 32 for providing angular orientation of the cake supply station relative to the needle-bonding station,

- a station 34 for eliminating non-needle-bonded fibers, if any,

a station 36 for evacuating cores 11 that are obtained with integrated bridging fibers.

Thus, it is possible to obtain a needle-bonding at an angle on both sides of the vertical axis, based on requirements.

Thus, the oblique bridging fibers 12 work perfectly to take up forces in particular when the panel that is made with these cores is subjected to a flexion and the vertical fibers work perfectly by eliminating the risks of delamination. Of course, the forces are often combined; all of the bridging fibers are subjected to forces.

The supply station comprises a double conveyor belt arranged on both sides of the needle- bonding station.

The station for depositing fibers comprises a cutter that ensures the cutting of the thread to constitute bridging fibers.

The process according to this invention makes it possible to propose a core 1 1 that is prepared for the panel manufacturers with the flexibility of possible combinations of all of the elements, namely: The nature of the cake made of light material, the nature of the type or types of bridging fibers, and the nature of the type or types of skin fibers.

It is also noted that it is thus possible to determine with great precision the quantity of bridging fibers when producing the core and the quantity and orientation of skin fibers. The density of the bridges, which is equivalent to the density of bridging fibers in the produced core can also be selected and applied so that it is possible to vary this density from some bridges or bridging fibers per m² bridges to several bridges or bridging fibers per cm². In preferred embodiments, the density is between 0,1 and 10 bridges per cm², preferably 0,2 to 6 per cm². Likewise, the installation geometry of the bridges can be controlled with a distribution, for example, in lines or in staggered rows.

It is consequently understood that the process for production of a core according to the process of the invention allows all of the combinations for the manufacture of a panel. It is possible to adapt the mechanical strength of the panel by choosing a suitable combination of bridging fibers, cakes, skins and resin, and to obtain panels with high resistance to delamination. Actually, meeting the requirements exactly prevents over-reinforcement, unnecessary consumption of raw material, and excess weight of the finished panels that then have to be transported, for example, over millions of kilometers on the truck that is equipped therewith.

Ultimately, this limitation of raw materials also makes it possible to reduce the costs and the quantities of material to be recycled at the end of service life.

Claims

1. A process for the production of a core (11 ) with integrated bridging fibers (12) for the manufacture of composite panels, comprising the steps of:

providing a cake (10) made of light material,

depositing bridging fibers (12) on at least one surface (18, 20) of the cake (10), and making these bridging fibers (12) partially or totally penetrate the cake (10).

2. The process according to claim 1 , comprising the steps of:

providing a cake (10) made of light material,

depositing excess bridging fibers (12) on at least one surface (18, 20) of the cake (10), making a portion of these bridging fibers (12) partially or totally penetrate the cake (10), removing excess bridging fibers (12) that are not used.

3. The process according to claim 1 or 2, wherein the needle-bonding is used to make the bridging fibers (12) penetrate the cake (10).

4. The process according to any of claims 1 to 3, wherein the penetration of the bridging fibers (12) is all the way through so that each bridging fiber (12) is accessible from both sides of the core.

5. The process according to any of claims 1 to 4, wherein the bridging fibers (12) are of different types.

6. The process according to any of claims 1 to 4, wherein the bridging fibers (12) are sections of threads that consist of bundles of braided filaments.

7. The process according to any of claims 1 to 6, wherein the bridging fibers (12) are inserted at an angle relative to the surfaces of the light-material cake (10).

8. The process according to any of claims 1 to 7, wherein the bridging fibres (12) are inserted at one, two or more defined angles relative to the surfaces of the cake (10).

9. A core that is obtained by the implementation of the process according to one of claims 1 to 8, comprising a light-material cake (10) and bridging fibers (12) of which at least one portion sticks out on at least one surface of said cake (10).

10. The core according to claim 9, wherein the density of the bridging fibers (12) is between 0,1 to 10 bridges per cm².

11. The core according to claim 9 or 10, wherein the distribution geometry of the bridging fibers (12) is linear or in staggered rows.

12. The core according to any of claims 9 to 1 1 , wherein the cake (10) is made of two or more materials.

13. A panel of composite material comprising a core (11 ) according to one of claims 9 to 12, and at least one skin on the core (1 1 ), its skin fibers (24) being immersed in a resin matrix, whereby said resin has also penetrated the bridging fibers (12).

14. The panel according to claim 13, wherein the ends of the bridging fibers (12) are immersed in the resin matrix with the skin fibers (24).

15. The panel according to claim 13 or 14, wherein the bridging fibers (12) are inclined relative to the plane of the core.

16. The panel according to any of claims 13 to 15, wherein the skin fibres (24) and the core (1 1 ) are made of different materials.

17. A device for the manufacture of a core according to one of claims 9 to 12, comprising: a station (26) for supply of light-material cakes (10),

a station (28) for deposition of bridging fibers on each cake,

a needle-bonding station (30),

a station (32) for angular orientation of the station (26) for supply of cakes relative to the needle-bonding station,

a station (36) for evacuating cores (11 ) with integrated bridging fibers.