WO2019038291A1

WO2019038291A1 - Material with a sandwich-type structure to be thermocompressed and manufacturing methods thereof

Info

Publication number: WO2019038291A1
Application number: PCT/EP2018/072570
Authority: WO
Inventors: Karim Behlouli; Justin MEROTTE
Original assignee: Eco - Technilin Sas
Priority date: 2017-08-22
Filing date: 2018-08-21
Publication date: 2019-02-28
Also published as: EP3672794A1; FR3070306A1; FR3070306B1

Abstract

The invention relates to a material (1) with a sandwich-type structure to be thermocompressed, comprising a core (2) arranged between a first skin (3) and a second skin (4), said first skin (3) comprising a first polymer matrix (3a), said second skin (4) comprising a second polymer matrix (4a), characterised in that said core (2) comprises a third polymer matrix (2a), wherein a porosity agent (5) configured to create a porosity in the core (2) is distributed, such that when said material (1) is thermocompressed, the first (3a) and second (4a) polymer matrices adhere to the third polymer matrix (2a), and the porosity agent (5) is further configured to maintain or increase said porosity in the core (2) when said material (1) is thermocompressed.

Description

THERMOCOMPRIMER SANDWICH-TYPE STRUCTURE MATERIAL AND METHODS OF MANUFACTURING THE SAME

The present invention relates to the field of materials to be thermocompromised, and relates in particular to a sandwich-type material thermocomprimer having a localized porosity and associated manufacturing processes.

The materials to be thermocompressed are especially used in the automotive field to produce, for example, door linings or rear shelves after thermocompression, the materials to be thermocompressed being generally constituted by a non-woven of natural fibers or mineral fibers mixed with thermoplastic fibers. The materials to be thermocompressed are intended to be thermocompressed in a mold in order to melt the thermoplastic fibers and to give the piece the desired shape depending on the final application.

European Patent Application EP1526214 A1 discloses a method of impregnating a fiber network with powder using an alternating electrostatic field created between two electrodes to produce a composite material. However, this method does not make it possible to precisely locate the powder in the thickness of the fibrous network, the powder being in fact impregnated throughout the thickness of the fibrous network by the alternating electrostatic field.

French patent application FR3027926 A1 discloses a process for producing a non-woven complex / active particles in pulverulent form, the active particles being particles of depolluting substance or particles intended to capture metals. However, these active particles do not allow to create a localized porosity in the nonwoven in order to obtain a significant gain on the mass of parts used for example in the automotive field.

European patent application EP1466042 A1 discloses a composite insulating material made of expanded microcells and a fibrous support. However, the expanded microcells are arranged throughout the thickness of the composite material and do not allow to create a localized porosity in the thickness of the composite material in order to concentrate the porosity at the core of the composite material, that is to say there where its effect is the least harmful for the mechanical performance of the composite material.

The present invention aims to overcome the drawbacks of the prior art by proposing a sandwich-type structure material comprising a core disposed between a first skin and a second skin, said core comprising a porosity agent, which allows to create a localized porosity in the core of the material in order to obtain a material of low basis weight and having mechanical performances similar to those of a standard material of higher grammage.

The subject of the present invention is therefore a material with a sandwich-type structure to be thermocompressed, comprising a core placed between a first skin and a second skin, said first skin comprising a first polymer matrix, said second skin comprising a second polymer matrix, characterized in that said core comprises a third polymer matrix in which is distributed a porosity agent configured to create a porosity in the core, so that when said material is thermocompressed, the first and second polymer matrices adhere to the third polymer matrix, and the porosity agent is further configured to maintain or increase said porosity in the core when said material is thermocompressed.

The first polymer matrix and the second polymer matrix may be the same.

Likewise, the third polymer matrix may be identical to the first and second polymer matrices.

Thus, the porosity agent makes it possible to create a porosity localized in the core of the material in order to obtain a material of low mass per unit area and having mechanical performances similar to those of a standard material of higher grammage. The manufacture of this material developing a sandwich structure allows a significant gain on the mass of parts used for example in the automobile. This material allows automotive parts manufacturers to lighten their structures by reducing the mass of semi-finished products.

Porosity means all the voids or pores of a solid material, these voids being filled by fluids (liquid or gas).

The thermocompression of the material allows the fusion of the polymer matrices and thus the link of the soul with the skins. Indeed, there must be adhesion between the skin polymers and that of the soul to prevent delamination. Conversely, the adhesion between the porosity agent and the polymer matrix of the core is not necessary.

The porosity being localized in the core of the material, one can thus qualify this structure of sandwich type presenting, on the surface, two skins and in the heart a airy soul and preferably thicker. The porosity is concentrated at the heart of the material, that is to say where its effect is the least harmful for the mechanical performance of the material.

The material to be thermocompressed is then thermocompressed in a thermocompression press. The heating is used to fuse the dies and to expand the porosity agent in the center of the material in the case where the porosity agent is an expandable agent. In the case where the porosity agent is an expanded agent, said foamed agent is already foamed before heating and retains its initial expansion after heating. The cooling then makes it possible to crystallize the dies and to make the piece rigid.

The advantages in terms of performance are the increase of the stiffness of the stack and the increase of the rigidity without preferential orientation.

Porosity has a direct impact on the mechanical performance of the material. Given the fact that bending is the most used solicitation mode in the automobile, it seems advisable to concentrate the elements having better mechanical properties on the skins of the material.

It is thus possible to take advantage of the porosity by controlling its location. Indeed, by concentrating it in the heart of the material, it is possible to obtain a sandwich type structure which has improved mechanical performance without increasing the mass of parts.

It should be noted that attempts to place the porosity agent alone between the two skins have not been conclusive since no adhesion exists between the agent porosity and the matrices of the skins, a delamination between the skins and the soul occurred.

According to a particular characteristic of the invention, the core further comprises core reinforcing fibers mixed with the third polymer matrix.

Thus, the core reinforcement fibers actively participate in the good mechanical properties of the soul. The thermocompression of the material allows the fusion of the third polymer matrix and thus the bond between the core reinforcement fibers and the third polymer matrix.

The core can thus be considered as a fibrous network bonded by polymer bridges. Within the pores of this network is the porosity agent, said porosity agent not playing a structuring role because there is no adhesion between the porosity agent and the composite reinforcing fibers - polymer matrix .

The third polymer matrix before thermocompression is in the form of fusible fibers, powder or polymer resin.

According to a particular characteristic of the invention, at least one of said first and second skins further comprises skin reinforcing fibers mixed with the associated polymer matrix.

Thus, the skin reinforcing fibers actively participate in the good mechanical properties of the associated skin. The thermocompression of the material allows the fusion of the first and second polymer matrices and thus the bond between the skin reinforcing fibers and the associated polymer matrix.

The skin-reinforcing fibers may be woven or non-woven, with a particular orientation or not. The skins are preferably made of a nonwoven combining skin reinforcing fibers and polymer matrix, these skins being produced by carding technology, the two skins preferably being identical in composition and thickness.

The first and second polymer matrices before thermocompression are in the form of fusible fibers, powder or polymer resin.

According to a particular characteristic of the invention, in each skin, the mass proportion of skin reinforcing fibers / associated polymer matrix is between 5% / 95% and 60% / 40%.

According to a particular characteristic of the invention, each of the first, second and third polymer matrices consists of at least one polymer such as polypropylene, polyethylene, polyethylene terephthalate and polyamide (6, 6-6, 11). . Other polymers may be contemplated by those skilled in the art without departing from the scope of the present invention.

It should be noted that the polymers of the skins and the core are not necessarily identical.

The choice of each polymer matrix is effected, for example, depending on the molding process, the temperature of use of the final part and the compatibility with the reinforcing fibers.

According to one particular characteristic of the invention, the core reinforcing fibers and, where appropriate, the skin reinforcing fibers are chosen from one or more of vegetable fibers such as flax, hemp, jute fibers. , kenaf or sisal, mineral fibers such as glass or basalt fibers, synthetic fibers such as carbon or aramid fibers, and polymeric fibers having a melting point higher than that of the associated polymer matrix.

The choice of the reinforcing fibers is effected, for example, depending on the molding process and the temperature of use of the final part.

According to a first embodiment of the invention, the core consists of a nonwoven comprising the third matrix of polymer mixed, if necessary, with the core reinforcing fibers, the porosity agent being distributed to inside the non-woven.

Thus, the nonwoven of the core is a fibrous network consisting of polymer fibers and, where appropriate, core reinforcing fibers such as plant fibers, the porosity agent being distributed in the pores of the network. porous nonwoven.

According to a second embodiment of the invention, the core consists of ground materials of the third polymer matrix mixed, where appropriate, with the core reinforcing fibers, the porosity agent being distributed between said ground materials.

Thus, the ground material can come from the grinding of a nonwoven made of polymer fibers and, where appropriate, core reinforcing fibers such as plant fibers.

Grinding has a double effect, it breaks the fibers by decreasing their lengths and it also divides the fibers by decreasing their beam diameters, the first effect being detrimental to the performances of the composites, the second effect being for its part beneficial.

The core is preferably composed of composite scraps of vegetable reinforcing fibers-polymer fibers which have been incorporated with a porosity agent, the skins are related to the soul in a correct way thanks to the presence of "bridges" of vegetable reinforcement fibers-polymer fibers connecting the two skins together and crossing the central part.

In order to offer the most competitive solution possible, the production of shreds integrates the reuse of non-woven manufacturing scrap. The manufacturing scrap can thus be crushed and reused in the core of the sandwich type material. In the same way, the crushed materials can come from the recycling of thermocompromised composites. Recycling therefore becomes an asset in terms of environmental impact, cost but also technical performance.

According to a particular characteristic of the invention, the ground materials have a particle size of between 1 mm and 20 mm.

The crushed materials are preferably derived from composite plates, generally non-woven, having a thickness of between 1 and 10 mm.

The choice of particle size is defined according to the thickness of the material and its compression ratio.

According to a first variant of the invention, the porosity agent is an expanded agent, such as hollow glass microbeads, making it possible to create a porosity in the core and to preserve it after the thermocompression.

Thus, hollow glass microspheres make it possible to create a porosity in the core and, during thermocompression, the presence of hollow glass microbeads in the core of the material limits the compressibility of the core. At an overall compression ratio identical to that of a standard material, the core of the material according to the invention is more porous than the standard material and the skins are less porous. A sandwich type structure is created.

The hollow glass microbeads are for example the EUROCELL300® product from Europerl.

With this type of expanded porosity agent, however, it is difficult to achieve a high compression ratio of the skins because the compression pressure would deteriorate the hollow glass microbeads.

According to a second variant of the invention, the porosity agent is an expandable agent, such as polymeric microcapsules containing a gas which is activated by expanding at a predefined temperature, making it possible to create a porosity in the core and to increase it after thermocompression.

Thus, the polymeric microcapsules contain a gas that activates by expanding at a certain temperature with or without water vapor, in order to increase the porosity in the core after thermocompression of the material.

There are many gases and many types of microcapsules. Their choice is made taking into account their expansion capacity, their activation temperature and their degradation temperature. These parameters must be compatible with the molding parameters. During thermocompression, the rise in temperature necessary for the melting of the matrix fibers also serves to activate the expansion of the microcapsules. They will generate a push compressing the skins against the walls of the hot mold. This phenomenon will improve the wetting between the fibers and the matrix. At the end of the heating step, the material has an "inflated" appearance in its heart. During cold compression, the expanded spheres are compressed and continue to overcompress the skins, thus creating a significant density difference between the soul and the skins. The end result is a material with a more porous core than the standard material and less porous skins than the standard material. Once again we find the sandwich structure. The compression ratio of the skins can be adjusted by changing the amount of expandable agent in the core.

The expandable porosity agent is, for example, Expancel® 950DU120 microspheres from AkzoNobel. Expancel® microspheres are thermoplastic spheres (acrylic copolymer) containing a combination of gases (isooctane and isopentane). During the rise in temperature, the gas expands and the thermoplastic capsule softens, allowing the increase in the volume contained. The average diameter of unexpanded Expancel® microspheres is between 28 and 38 μm. Once completely expanded, their density is less than 9 kg / m ³ . The initiation of the expansion is carried out between 133 ° C. and 143 ° C. with a maximum temperature before degradation of 205 ° C. This expandable agent is therefore compatible with the processing temperatures of the polypropylene matrix composites (200 ° C.).

Expandable polystyrene beads (eg BASF Styropor® F95 Series) can also be used. In this case, to activate the expansion, a small amount of water is sprayed on the lower part of the material before introduction into the thermocompression mold. During the heating stage, the water vaporizes and allows the balls to swell.

According to a particular characteristic of the invention, the mass incorporation of the porosity agent into the core is between 1% and 30%. This percentage mass incorporation of the porosity agent depends on the desired skin compression ratio and the size of the expanded microspheres.

According to a particular characteristic of the invention, the mass of the core is between 10% and 50% by total weight of sandwich-type structure material.

In the case where the porosity agent is expandable, the more agent will be expandable in the core, the more the skins will be thick to prevent piercing of the skins by the expandable agent during the expansion thereof .

According to a particular characteristic of the invention, the thickness of each skin is between 0.5 mm and 5 mm.

According to a particular characteristic of the invention, the thickness of the core is between 1 mm and 9 mm.

The maximum total thickness of the material to be thermocompressed is a maximum of 10 mm.

The present invention also relates to a method for manufacturing a sandwich-type structure material to be thermocompressed according to the first embodiment described above, said manufacturing method comprising the following steps: the supply of the first and second skins; the supply of the nonwoven of the soul; sprinkling the porosity agent on the nonwoven of the core; incorporating the porosity agent into the nonwoven of the core using at least one of an alternating electrostatic field, centrifugation, air pressure, mechanical pressure and partial vacuum; the disposition of the soul between the first and second skins; and assembling the core and the first and second skins by needling and / or thermoling.

Thus, this first method allows the preferential location of the porosity in the center of the thickness of the material and avoids the migration of the porosity agent to the skin.

It should be noted that, in the manufacturing method described above, the nonwoven of the core could also already contain the porosity agent, without departing from the scope of the present invention, the alternating electrostatic field, centrifugation, air pressure, mechanical pressure and / or partial vacuum are then not necessary. Such a nonwoven of the core already containing the porosity agent may, for example, be manufactured using one of the two manufacturing methods described below.

The subject of the present invention is furthermore a method for manufacturing a sandwich-type structure material to be thermocompressed according to the second embodiment described above, said manufacturing method comprising the following steps: the supply of the first and second skins ; the supply of crushed souls; mixing the ground materials with the porosity agent; sprinkling the mixture of ground material and porosity agent on one of the first and second skins; the arrangement of the other of the first and second skins on the mixture sprinkled with ground material and porosity agent; and assembling the core and the first and second skins by needling and / or thermoling.

Thus, this second method also allows the preferential location of the porosity in the center of the thickness of the material and avoids the migration of the porosity agent to the skin. During the mixing of the ground materials with the porosity agent, the microspheres of the porosity agent are captured by the bare fibers located at the periphery of the ground materials.

The subject of the present invention is also another method of manufacturing a sandwich-type structure material to be thermocompressed according to the second embodiment described above, said manufacturing method comprising the following steps: the supply of a veil of cards; the supply of crushed souls; mixing the ground materials with the porosity agent; sprinkling the mixture of ground material and porosity agent on the card web; the topping of the card web on which said mixture is sprinkled, such that said mixture is at the center of the thickness of the web; and consolidating the sandwich-like structure material by needling and / or thermoling.

Thus, this third method also allows the preferential location of the porosity in the center of the thickness of the material and avoids the migration of the porosity agent to the skin.

This technique of dusting and then coating allows to locate the porosity agent at different positions in the thickness of the material.

During the mixing of the ground materials with the porosity agent, the microspheres of the porosity agent are captured by the bare fibers located at the periphery of the ground materials.

The core is preferably composed of a mixture of composite non-woven composite scrap and a porosity agent. The ratio drops / porosity agent may vary according to the need for rigidity of the material and the cost of manufacturing. This mixture is integrated in the heart of the non-woven by dusting in the center of the cardboard veil. The whole is consolidated by needling or hot compression.

The subject of the present invention is also a method for manufacturing a material with a sandwich-type structure to be thermocompressed according to the first embodiment described above, said manufacturing method comprising the following steps: the supply of a card web ; sprinkling the porosity agent on the card web; the covering of the card web on which the porosity agent is sprinkled, such that said porosity agent is at the center of the thickness of the coated web; and consolidating the sandwich-like structure material by needling and / or thermoling.

The advantages in terms of manufacturing are as follows: no change of tools required, possibility of varying the thickness of the core in the same material, possibility of recycling the manufacturing waste of customers by integrating them into the product, and deformability of the reinforcement retained during molding.

To better illustrate the object of the present invention will be described below, by way of illustration and not limited to three preferred embodiments, with reference to the accompanying drawings.

On these drawings:

- Figure 1 is a sectional view of a sandwich type structure material according to a first variant of a first embodiment of the invention; - Figure 2 is a sectional view of a sandwich type structure material according to a first variant of a second embodiment of the invention;

- Figure 3 is a sectional view of a sandwich type structure material according to a second variant of the second embodiment of the invention;

- Figure 4 is a sectional view of a crushed core of the material of Figure 3;

- Figure 5 is a side view of a sandwich-type material manufacturing device according to the first embodiment;

Figure 6 is a side view of a sandwich structure type manufacturing device according to the second embodiment;

- Figure 7 is a top view of another device for manufacturing a sandwich type structure material according to the second embodiment;

- Figure 8 is a sectional view of a sandwich type structure material according to a third variant of the second embodiment of the invention; and

- Figure 9 is a sectional view of a sandwich type structure material according to a second variant of the first embodiment of the invention.

Referring to Figure 1, it can be seen that there is shown a sandwich type structure material 1 according to a first variant of a first embodiment of the invention.

The material with a sandwich-type structure 1 is a material to be thermocompressed, comprising a core 2 placed between a first skin 3 and a second skin 4. The first skin 3 comprises fibers of the first polymer matrix 3a, and the second skin 4 comprises fibers of the second polymer matrix 4a, the fibers of the first polymer matrix 3a and the fibers of the second polymer matrix 4a preferably being identical. .

The first and second polymer matrices 3a, 4a are in the form, before thermocompression, of fusible fibers, but could also be in the form of powder or polymer resin, without departing from the scope of the present invention.

The first skin 3 further comprises skin reinforcing fibers 3b mixed with the fibers of the first polymer matrix 3a, and the second skin 4 further comprises skin reinforcing fibers 4b mixed with the fibers of the second polymer matrix 4a. the skin reinforcing fibers 3b, 4b of the first and second skins 3, 4 are preferably identical. The skin reinforcing fibers 3b, 4b actively participate in the good mechanical properties of the skins 3, 4. The skin reinforcing fibers 3b, 4b are non-woven, but could also be woven, with a particular orientation or not, without any depart from the scope of the present invention.

It should be noted that the first and second skins 3, 4 could also not comprise skin reinforcing fibers 3b, 4b, without departing from the scope of the present invention.

The skins 3, 4 thus consist of a nonwoven combining skin reinforcing fibers 3b, 4b and polymer matrix fibers 3a, 4a, the skins 3, 4 being produced by the carding technology, the skins 3, 4 being preferably identical in composition and thickness. In each skin 3, 4, the mass proportion of skin reinforcing fibers 3b, 4b / polymer matrix fibers 3a, 4a is preferably between 5% / 95% and 60% / 40%.

The core 2 comprises fibers of the third polymer matrix 2a and core reinforcing fibers 2b mixed with the fibers of the third polymer matrix 2a, the core reinforcing fibers 2b actively participating in the good mechanical properties of the soul 2.

It should be noted that the core 2 could also not include core reinforcing fibers 2b, without departing from the scope of the present invention.

The third polymer matrix 2a is in the form, before thermocompression, of fusible fibers, but could also be in the form of powder or polymer resin, without departing from the scope of the present invention.

The core 2 thus consists of a fibrous network, of nonwoven type, bonded by polymer bridges.

The core 2 further comprises a porosity agent 5 distributed in the fibrous network consisting of the fibers of the third polymer matrix 2a and the core reinforcing fibers 2b, said porosity agent 5 being configured to create a porosity in the core 2, such that when the material 1 is thermocompressed, the first, second and third polymer matrices 3a, 4a, 2a melt, the first and second polymer matrices 3a, 4a adhere to the third polymer matrix 2a, and the porosity agent 5 makes it possible to maintain or increase said porosity in the core 2 when said material 1 is thermocompressed.

The porosity agent 5, which is in granular or powdery form, is housed within the pores of the fibrous network of the core 2, the porosity agent 5 not playing a structuring role because no adhesion exists between the porosity agent 5 and the fibrous network of the core 2. It should be noted, however, that such adhesion is not excluded in the context of the present invention.

The porosity agent 5 thus makes it possible to create a porosity localized in the core 2 of the material 1 in order to obtain a material of low mass per unit area and having mechanical performances similar to those of a standard material of higher grammage. The manufacture of this material 1 developing a sandwich structure allows a significant gain on the mass of the parts used for example in the automobile, this material 1 allowing for example the manufacturers of auto parts to lighten their structures by reducing the weight of the reinforcements .

The thermocompression of the material 1 allows the fusion of the polymer matrices 2a, 3a, 4a and thus the connection of the core 2 with the skins 3, 4.

The material 1 thus has on the surface two skins 3, 4 and in the core a core 2 ventilated and of greater thickness. The porosity is concentrated in the core of the material 1, that is to say where its effect is the least harmful for the mechanical performance of the material 1.

Each of the first, second and third polymer matrices 3a, 4a, 2a consists of at least one polymer such as polypropylene, polyethylene, polyethylene terephthalate and polyamide (6, 6-6, 11).

The polymers of the skins 3, 4 and the core 2 are not necessarily identical.

The core reinforcing fibers 2b and the skin reinforcing fibers 3b, 4b are selected from one or more of vegetable fibers such as flax fibers, hemp, jute, kenaf or sisal, mineral fibers such as glass or basalt fibers, synthetic fibers such as carbon or aramid fibers, and polymer fibers having a melting point higher than that of the associated polymer matrix.

The porosity agent 5 is one of an expanded agent and an expandable agent, said expanded and expandable agents being described in more detail in Figures 2 and 3, respectively.

The mass incorporation of the porosity agent in the core 2 is preferably between 1% and 30%.

The mass of the core 2 is preferably between 10% and 50% by total weight of material with sandwich structure 1.

The thickness of each skin 3, 4 is preferably between 0.5 mm and 5 mm, and the thickness of the core 2 is preferably between 1 mm and 9 mm, the total thickness of the material to be thermocompressed. 1 being less than or equal to 10 mm.

Referring to Figure 2, it can be seen that there is shown a sandwich type structure material 11 according to a first variant of a second embodiment of the invention.

The elements common between the first embodiment of the invention in FIG. 1 and this first variant of the second embodiment of the invention bear the same reference numeral to which 10 has been added, and will not be described in more detail. here when they are identical structures.

The first and second skins 13, 14 of the material to be thermocompressed 11 are identical to those of the material to be thermocompress 1 according to the first variant of the first embodiment.

The core 12 of the material 11 is made of thermocompressed non-woven fabric grinds 16, each grind 16 being composed of the third crystallized polymer matrix 12a in which the core reinforcing fibers 12b are trapped, certain ends of the reinforcing fibers core 12b leaving the third crystallized polymer matrix 12a, the porosity agent 15 being distributed between said ground material 16.

The ground material 16 is preferably derived from the grinding of composite non-woven fabric waste in which the porosity agent 15 has been incorporated. The skins 13, 14 are bonded to the core 12 in a correct manner thanks to the presence of bridges »of reinforcing fiber-polymer fibers connecting the two skins 13, 14 between them and passing through the core 12.

The ground material 16 preferably has a particle size of between 1 mm and 20 mm, the choice of particle size being defined as a function of the thickness of the material 11 and its compression ratio.

In the first variant of this second embodiment, the porosity agent 15 is an expanded agent, namely hollow glass microbeads, making it possible to create a porosity in the core 12 and to retain the porosity after thermocompression of the material 11. .

The hollow glass microbeads 15 thus make it possible to create a porosity in the core 12, then, during thermocompression, the presence of the hollow glass microbeads 15 at the core of the material 11 makes it possible to limit the compressibility of the core 12. At a rate of overall compression identical to that of a standard material, the core 12 of material 11 is more porous than that of the standard material and the skins 13, 14 are less porous.

The hollow glass microbeads 15 are, for example, the EUROCELL300® product from Europerl. It should be noted that with this type of expanded porosity agent, however, it is difficult to achieve a high compression ratio of the skins 13, 14 because the compression pressure would deteriorate the hollow glass microbeads 15.

With reference to FIG. 3, it can be seen that there is shown a sandwich-like structure material 21 according to a second variant of the second embodiment of the invention.

The common elements between the first variant of the second embodiment of the invention in FIG. 2 and this second variant of the second embodiment of the invention bear the same reference number to which 10 has been added, and will not be described. in more detail here when they are of identical structures.

The first and second skins 23, 24 of the material to be thermocompressed 21 are identical to those 13, 14 of the material to be thermocompressed 11 according to the first variant of the second embodiment.

The shreds 26 of the core 22 of the material to be thermocompressed 21 are identical to those 16 of the core 12 of the material to be thermocompressed 11 according to the first variant of the second embodiment.

In the second variant of the second embodiment, the porosity agent 25 is an expandable agent, namely polymeric microcapsules containing a gas which is activated by expanding at a predefined temperature with or without the presence of water vapor. , thus making it possible to create a porosity in the soul 22 and to increase the porosity after the thermocompression of the material 21.

There are many gases and many types of microcapsules for the expandable porosity agent 25. Their choice is made taking into account their expansion capacity, their activation temperature and their degradation temperature. These parameters must be compatible with the molding parameters. During thermocompression, the rise in temperature necessary for melting the fusible fibers 23a, 24a also serves to activate the expansion of the microcapsules 25. They will generate a thrust compressing the skins 23, 24 against the walls of the hot mold. This phenomenon will improve the wetting between the reinforcing fibers 23b, 24b and the polymer matrix fibers 23a, 24a. At the end of the heating step, the material 21 has an "inflated" appearance in its heart. During cold compression, the expanded spheres are compressed and continue to overcompress the skins 23, 24, thus creating a significant density difference between the core 22 and the skins 23, 24. The final result is a material 21 having a core 22 more porous than the standard material and skins 23, 24 less porous than the standard material. The compression ratio of the skins 23, 24 can be adjusted by changing the amount of expandable agent in the core 22.

The expandable porosity agent 25 is, for example, Expancel® 950DU120 microspheres from AkzoNobel. Expancel® microspheres are thermoplastic spheres (acrylic copolymer) containing a combination of gases (isooctane and isopentane). During the rise in temperature, the gas expands and the thermoplastic capsule softens, allowing the increase in the volume contained. Expandable polystyrene beads (eg BASF Styropor® F95 Series) can also be used. In this case, to activate the expansion, a small amount of water is sprayed on the lower part of the material 21 before introduction into the thermocompression mold. During the heating stage, the water vaporizes and allows the balls to swell.

It should be noted that, in the case where the porosity agent 25 is expandable, the more expandable agent 25 in the core 22, the more skins 23, 24 will have to be thick to prevent piercing of the skins. ,

24 by the expandable agent 25 during expansion thereof.

With reference to FIG. 4, it can be seen that there is shown a ground 26 of the core 22 of the material to be thermocompressed 21.

The ground 26 is derived from the grinding of a thermocompressed composite nonwoven, the composite nonwoven comprising, before thermocompression, fusible fibers mixed with reinforcing fibers 22b. The thermocompression of the composite nonwoven allows the fusion and crystallization of the fusible fibers, the reinforcing fibers 22b being then trapped in the crystallized polymer matrix 22a.

After grinding the thermocompressed composite nonwoven, some ends of the reinforcing fibers 22b protrude from the crystallized polymer matrix 22a.

When mixing the expandable porosity agent

With the ground material 26, the porosity agent microcapsules 25 are captured by the naked reinforcing fibers 22b located at the periphery of the shreds 26.

The thermocompression of the material 21 then allows the microcapsules of porosity agent 25 to expand between the shreds 26 and thus increase the porosity in the core 22 of the material 21.

Referring to Figure 5, it can be seen that there is shown a device for manufacturing the sandwich type structure material 1 according to the first variant of the first embodiment of the invention.

The manufacturing device 30 comprises a dusting device 31, two electromagnetic alternating field creation electrodes 32, two guide rollers 33 and a needling device 34.

The manufacturing device 30 makes it possible to implement the method of manufacturing the sandwich-type structure material 1 according to the first variant of the first embodiment, said manufacturing method comprising the following steps: the supply of the first and second skins 3, 4; the supply of the nonwoven of the core 2; the dusting of the porosity agent 5 on the nonwoven of the core 2 with the aid of the dusting device 31 which is disposed above the nonwoven of the core 2; the incorporation of the porosity agent 5 in the nonwoven of the core 2 by means of an alternating electrostatic field created by the two electrodes 32 which are arranged respectively below and above the nonwoven of the core 2 downstream of the dusting device 31, the arrangement of the core 2 between the first and second skins 3, 4 with the aid of the guide rollers 33 which guide the first and second skins 3, 4 respectively close to the lower and upper faces of the core 2; and assembling the core 2 and the first and second skins 3, 4 by means of the needling device 34.

It should be noted that the incorporation of the porosity agent 5 in the nonwoven of the core 2 could also be carried out using a centrifugation, a pressure air, mechanical pressure or partial vacuum, without departing from the scope of the present invention.

It should be noted that the assembly of the core 2 and the first and second skins 3, 4 could also be achieved by thermobonding, without departing from the scope of the present invention.

The first and second skins 3, 4 and the nonwoven of the core 2 are preferably made using carding devices (not shown in FIG. 5).

Thus, this manufacturing device 30 allows the preferential location of the porosity in the center of the thickness of the material 1 and avoids the migration of the porosity agent 5 to the skins 3, 4.

The material to be thermocompressed 1 is then thermocompressed in a thermocompression press. The heating is used to fuse the polymer matrix fibers 2a, 3a, 4a and to expand the porosity agent 5 in the center of the material 1 in the case where the porosity agent 5 is an expandable agent. The cooling then makes it possible to crystallize the polymer matrices 2a, 3a, 4a and to make the part rigid.

It should be noted that, in the manufacturing method described above, the nonwoven of the core 2 could also already contain the porosity agent 5, without departing from the scope of the present invention, the device for Dusting 31 and the two electrodes 32 are then not necessary.

Referring to Figure 6, it can be seen that there is shown a manufacturing device 40 of the sandwich type structure material 21 according to the second variant of the second embodiment of the invention.

It should be noted that this manufacturing device 40 is also suitable for the manufacture of the material sandwich-type structure 11 according to the first variant of the second embodiment of the invention.

The manufacturing device 40 comprises a dusting device 41, a guide roller 42 and a needling device 43.

The manufacturing device 40 makes it possible to implement the process for manufacturing the thermocompress sandwich structure material 21 according to the second variant of the second embodiment, said manufacturing method comprising the following steps: the supply of the first and second skins 23, 24; the supply of ground material 26 in the dusting device 41; mixing the ground material 26 with the porosity agent 25 in the dusting device 41; sprinkling the mixture of ground material 26 and porosity agent 25 on the first skin 23 with the aid of the dusting device 41 which is disposed above the first skin 41; the arrangement of the second skin 24 on the powdered mixture of ground material 26 and porosity agent 25 by means of the guide roller 42; and assembling the core 22 and the first and second skins 23, 24 through the needling device 43.

It should be noted that the microspheres of the porosity agent 25 captured by the naked fibers 22b located at the periphery of the shreds 26 have not been shown in FIG. 6 to simplify the drawing.

It should be noted that the assembly of the core 22 and the first and second skins 23, 24 could also be made by thermobonding, without departing from the scope of the present invention.

The first and second skins 23, 24 are preferably made using carding devices (not shown in Figure 6). Thus, this manufacturing device 40 allows the preferential localization of the porosity at the center of the thickness of the material 21 and makes it possible to avoid the migration of the porosity agent 25 towards the skins 23, 24.

The material to be thermocompressed 21 is then thermocompressed in a thermocompression press. The heating is used to fuse the polymer matrices 22a, 23a, 24a and to expel the porosity agent 25 located in the center of the material 21. The cooling then makes it possible to crystallize the polymer matrices 22a, 23a, 24a and to make the rigid piece.

Referring to Figure 7, it can be seen that there is shown another manufacturing device 50 of a sandwich-like structure material 121 according to a third variant of the second embodiment of the invention such as as shown in Figure 8.

The common elements between the second variant of the second embodiment of the invention in FIG. 3 and this third variant of the second embodiment of the invention bear the same reference numeral, and will not be described in more detail here when they are identical structures.

It should be noted that this manufacturing device 50 is also suitable for the manufacture of a material with a sandwich-type structure using shreds 16 mixed with an expanded agent 15.

The manufacturing device 50 comprises a carding device 51, a dusting device 52, a layering device 53 and a needling device 54.

The manufacturing device 50 makes it possible to implement another method of manufacturing the sandwich-type structure material to be thermocompressed 121 according to the third variant of the second embodiment, said other manufacturing method comprising the following steps: the creation of a card web 55 by means of the carding device 51, the card web 55 being a nonwoven composite of the same composition as the first and second skins 23, 24 final; providing the ground material 26 in the dusting device 52; mixing the ground material 26 with the porosity agent 25 in the dusting device 52; sprinkling the ground mixture 26 and porosity agent 25 on the card web 55 by means of the dusting device 52 which is disposed above the card web 55 downstream of the carding device 51; the topping of the card web 55, on which said mixture is sprinkled, by means of the batting device 53, such that said mixture is at the center of the thickness of the web 55 coated; and consolidating the sandwich type structure material 121 through the needling device 54.

Reference numeral 122 in FIG. 8 represents the plies of batting web 55 after the lay-up step.

It should be noted that the microspheres of the porosity agent 25 captured by the naked fibers 22b located at the periphery of the shreds 26 have not been shown in FIG. 7 to simplify the drawing.

It should be noted that the consolidation of the sandwich type structure material 121 could also be carried out by thermoling without departing from the scope of the present invention.

Thus, this manufacturing device 50 allows the preferential location of the porosity in the center of the thickness of the material 121 and makes it possible to avoid the migration of the porosity agent 25 towards the skins 23, 24. The material to be thermocompressed 121 is then thermocompressed in a thermocompression press. The heating makes it possible to fuse the polymer matrices 22a, 23a, 24a and to expand the porosity agent 25 located in the center of the material 121. The cooling then makes it possible to crystallize the polymer matrices 22a, 23a, 24a and to make the polymer rigid piece.

This dusting and then topping technique makes it possible to locate the porosity agent 25 at different positions in the thickness of the material 121.

The manufacturing device 50 could also be used for the manufacture of a sandwich type structure material 101 according to a second variant of the first embodiment of the invention as represented in FIG. 9.

The elements common between the first variant of the first embodiment of the invention in FIG. 1 and this second variant of the first embodiment of the invention bear the same reference numeral, and will not be described in more detail here when they are identical structures.

The manufacturing device 50 makes it possible to implement another method of manufacturing the thermocompress sandwich structure material 101 according to the second variant of the first embodiment, said other manufacturing method comprising the following steps: the creation of a web 55 with the aid of the carding device 51, the card web 55 being a composite nonwoven of the same composition as the first and second skins 3, 4; sprinkling the porosity agent 5 (instead of the shreds 26 shown in FIG. 7) on the card web 55 by means of the dusting device 52 which is arranged above the web of card 55 downstream of the carding device 51; the covering of the card web 55, onto which said porosity agent 5 is sprinkled, by means of the batting device 53, such that said porosity agent 5 is at the center of the thickness of the web 55 coated; and consolidating the sandwich structure material 101 via the needling device 54.

Reference numeral 102 in FIG. 9 represents the batting plies of the card web 55 after the lapping step.

It should be noted that the consolidation of the sandwich-type structure material 101 could also be achieved by thermoling without departing from the scope of the present invention.

This dusting and then topping technique makes it possible to locate the porosity agent 5 at different positions in the thickness of the material 101.

The advantages of the invention in terms of manufacture are as follows: no change of tools required, possibility of varying the thickness of the core in the same material, possibility of recycling the manufacturing waste of customers by integrating them in the product, and deformability of the reinforcement retained during molding.

Claims

1 - Material with a sandwich structure (11; 21; 121) to be thermocompressed, comprising a core (12; 22) disposed between a first skin (13; 23) and a second skin (14; 24), said first skin ( 13; 23) comprising a first polymer matrix (13a; 23a), said second skin (14; 24) comprising a second polymer matrix (14a; 24a), said core (12; 22) comprising a third polymer matrix ( 12a; 22a) in which a porosity agent (15; 25) configured to create a porosity in the core (12; 22) is distributed so that when said material (11; 21; 121) is thermocompressed, the first (13a; 23a) and second (14a; 24a) polymer matrices adhere to the third polymer matrix (12a; 22a), and the porosity agent (15; 25) is further configured to maintain or increase said porosity in the core (12; 22) when said material (11; 21; 121) is thermocompressed, characterized in that the core (12; 22) consists of ground material (16; 26) of the third polymer matrix (12a; 22a), the porosity agent (15; 25) being distributed between said ground material (16; 26).

2 - sandwich-type structure material (11; 21; 121) according to claim 1, characterized in that the ground material (16; 26) of the core (12; 22) further comprises reinforcing fibers of core (12b; 22b) mixed with the third polymer matrix (12a; 22a).

Characterized in that at least one of said first (13; 23) and second (14; 24) skins further comprising skin reinforcing fibers (13b, 14b, 23b, 24b) mixed with the associated polymer matrix (13a, 14a, 23a, 24a). 4 - material with a sandwich-like structure (11; 21; 121) according to claim 3, characterized in that in each skin (13, 14; 23, 24), the proportion by mass of skin reinforcing fibers ( 13b, 14b, 23b, 24b) / associated polymer matrix (13a, 14a, 23a, 24a) is between 5% / 95% and 60% / 40%.

5 - material with sandwich structure (11; 21; 121) according to one of claims 1 to 4, characterized in that each of the first (13a; 23a), second (14a; 24a) and third (12a; 22a) polymer matrix consists of at least one polymer such as polypropylene, polyethylene, polyethylene terephthalate and polyamide (6, 6-6, 11).

6 - Material with a sandwich-type structure (11; 21; 121) according to one of Claims 2 to 5, characterized in that the core reinforcing fibers (12b; 22b) and, if appropriate, the fibers skin reinforcement (13b, 14b; 23b, 24b) are selected from one or more of vegetable fibers such as flax, hemp, jute, kenaf or sisal fibers, mineral fibers such as glass or basalt, synthetic fibers such as carbon or aramid fibers, and polymer fibers having a melting point higher than that of the associated polymer matrix.

7 - Material having a sandwich structure (11;

21; 121) according to one of claims 1 to 6, characterized in that the ground material (16; 26) have a particle size of between 1 mm and 20 mm.

8 - Material with a sandwich-like structure (11) according to one of claims 1 to 7, characterized in that the porosity agent (15) is an expanded agent, such as hollow glass microspheres, which makes it possible to create a porosity in the core (12) and keep it after thermocompression.

9 - material with sandwich structure (21; 121) according to one of claims 1 to 7, characterized in that the porosity agent (25) is an expandable agent, such as polymeric microcapsules containing a gas which activates by expanding to a predefined temperature, to create a porosity in the core (22) and increase it after thermocompression.

10 - Material with a sandwich-type structure (11; 21; 121) according to one of Claims 1 to 9, characterized in that the mass incorporation of the porosity agent (15; 25) into the core ( 12; 22) is between 1% and 30%.

11 - Material with sandwich structure (11; 21; 121) according to one of claims 1 to 10, characterized in that the mass of the core (12; 22) is between 10% and 50% by weight. total mass of sandwich structure material (11; 21; 121).

12 - material with sandwich structure (11; 21; 121) according to one of claims 1 to 11, characterized in that the thickness of each skin (13, 14; 23, 24) is between 0, 5 mm and 5 mm.

13 - Material having a sandwich structure (11;

21; 121) according to one of claims 1 to 12, characterized in that the thickness of the core (12; 22) is between 1 mm and 9 mm. 14 - Method for manufacturing a sandwich-type structure material (11; 21) to be thermocompressed according to one of claims 1 to 13, said manufacturing method comprising the following steps: - supplying the first and second skins (13, 14; 23, 24);

- supplying the ground material (16; 26) of the core (12; 22);

- mixing the ground material (16; 26) with the porosity agent (15; 25);

- sprinkling the mixture of ground material (16; 26) and porosity agent (15; 25) on one of the first and second skins (13, 14; 23, 24);

- the arrangement of the other of the first and second skins (13, 14; 23, 24) on the sprinkled mixture of ground material (16;

26) and porosity agent (15; 25); and

assembling the core (12; 22) and the first and second skins (13, 14; 23, 24) by needling and / or heat-sealing.

15 - Process for manufacturing a sandwich-type structure material (121) to be thermocompressed according to one of claims 1 to 13, said manufacturing method comprising the following steps:

- supplying a card web (55);

- supplying the ground material (16; 26) of the core (12; 22);

- mixing the ground material (16; 26) with the porosity agent (15; 25);

- sprinkling the mixture of ground material (16; 26) and porosity agent (15; 25) on the card web (55);

- The topping of the card web (55) on which is sprinkled said mixture, such that said mixture is at the center of the thickness of the web (55) coated; and

- The consolidation of the sandwich-type structure material (121) by needling and / or thermoling.