Acoustic decoupling panel

Abstract

The invention relates to an acoustic decoupling panel (1) intended for lining a floor or the underbody (2) of a motor vehicle, said panel being based on a thermo-compressed mixture comprising: between 65 and 85% by weight of elastically compressible polyurethane foam flakes (3); between 10 and 25% by weight of two-component fibers (4) for bonding said flakes together, said fibers comprising a core fusible at a first temperature and a sheath fusible at a second temperature lower than said first temperature, said flakes having been bonded together by melting said sheath; between 5 and 15% by weight of pre-oxidized polyacrylonitrile fibers (5), so as to improve its resistance to combustion. Figure 1

Description

Title of the invention: Acoustic decoupling panel

[0001] The invention relates to an acoustic decoupling panel intended to line a floor or apron of a motor vehicle, and a lining assembly comprising such a panel.

[0002] It is known to produce an acoustic decoupling panel intended to cover a floor or the apron of a motor vehicle, said panel being based on a thermo-compressed mixture comprising: • between 65 and 85% by weight of elastically compressible polyurethane foam flakes, • between 10 and 25% by weight of bi-component fibers for bonding said flakes together, said fibers comprising a core fusible at a first temperature and a sheath fusible at a second temperature lower than said first temperature, said flakes having been bonded together by melting said sheath.

[0003] However, the applicant observed that such a panel might not meet the combustibility tests - measured by flame propagation speed - in force in the automotive industry, particularly in areas of said panel having a density of less than about 80 kg / m3.

[0004] The fact that low density zones are so combustible is explained a priori by the large quantity of air they contain, which is conducive to combustion.

[0005] This results in the need to produce a panel of significant mass to meet the combustibility requirements, which is detrimental to the desired weight reduction for motor vehicles.

[0006] The invention aims to overcome this drawback.

[0007] To this end, and according to a first aspect, the invention proposes an acoustic decoupling panel intended to cover a floor or the apron of a motor vehicle, said panel being based on a thermo-compressed mixture comprising: • between 65 and 85% by weight of elastically compressible polyurethane foam flakes, • between 10 and 25% by weight of bi-component fibers for bonding said flakes together, said fibers comprising a core fusible at a first temperature and a sheath fusible at a second temperature lower than said first temperature, said flakes having been bonded together by melting said sheath,

[0008] said composite panel further comprising between 5 and 15% by weight of pre-oxidized polyacrylonitrile (PAN) fibers, so as to improve its resistance to combustion.

[0009] It is specified here that the manufacture of pre-oxidized PAN filaments includes a step of exposing said filaments to air at a temperature between 200 and 350°C.

[0010] Such a partial pyrolysis operation causes a break in the molecular chains of polyacrylonitrile and the formation of cyclic structures.

[0011] It should be noted that pre-oxidized polyacrylonitrile fibers are known to constitute intermediate fibers in the production of carbon fibers from further pyrolysis.

[0012] With the proposed arrangement, a notable improvement in the panel's resistance to combustion is observed, including in its low density areas, for example on the order of 50 kg / m3.

[0013] This results in the possibility of obtaining a lightweight panel with a resistance to combustion that meets the requirements in force in the automotive industry.

[0014] It should be noted that the choice of such pre-oxidized fibers to achieve this result follows numerous tests carried out by the applicant using other methods, in particular by: • the addition of polyester fibers treated with a flame retardant; this method did not achieve the expected resistance to combustion, even with high-density panels, • The addition of liquid resin - notably by spraying - impregnating the foam flakes made it possible to obtain satisfactory resistance to combustion with low density panels; however, the proper coating of the flakes by the resin proved complex to implement, which led to abandoning this method.

[0015] Finally, it should be noted that the applicant unexpectedly observed that the presence of such pre-oxidized PAN fibers reduces the sticking of the panel against the mold during its thermo-compression molding, thus facilitating its manufacture.

[0016] According to other aspects, the invention proposes a trim assembly comprising such a panel.

[0017] Other features and advantages of the invention will become apparent in the following description, made with reference to the attached figure:

[0018] [Fig.1] which is a schematic partial cross-sectional view of an assembly comprising a panel according to the invention, said assembly being laid over a floor or apron of a motor vehicle.

[0019] Firstly, an acoustic decoupling panel 1 intended for lining a floor - in particular a passenger compartment or trunk - or a firewall 2 of a motor vehicle is described, said panel being based on a thermo-compressed mixture comprising: • between 65 and 85% by weight of elastically compressible polyurethane foam flakes, • between 10 and 25% by weight of bi-component fibers 4 for bonding said flakes together, said fibers comprising a core fusible at a first temperature and a sheath fusible at a second temperature lower than said first temperature, said flakes having been bonded together by melting said sheath,

[0020] said mixture further comprising between 5 and 15% by weight of pre-oxidized polyacrylonitrile (PAN) fibres 5, so as to improve its resistance to combustion.

[0021] In particular, the mixture comprises: • 70 to 80% by weight of polyurethane foam flakes, • 15 to 20% by weight of bi-component fibers 4, • 5 to 10% by weight of pre-oxidized polyacrylonitrile fibers 5.

[0022] According to one embodiment, the panel 1 has at least one area with a density less than 80 kg / m3 - and in particular between 50 and 60 kg / m3 - said area having the expected resistance to combustion despite its low density.

[0023] According to one embodiment, the area(s) with a density less than 80 kg / m3 extend over at least 30% of the surface of panel 1.

[0024] Flame propagation speed measurements carried out - according to the standard ISO 3795 in force at the date of application - on test specimens taken from a reference panel (free of pre-oxidized fibers) and a panel 1 according to the invention lead to the following results: • reference test specimen (density: 80 kg / m3): 99 mm / minute, • test specimen according to the invention (density: 50 kg / m3): 84 mm / minute.

[0025] It is noted that the addition of pre-oxidized fibers in the composition of the panel 1 allows for a significant improvement in its resistance to combustion while also allowing for a drastic reduction in weight.

[0026] According to one embodiment, the pre-oxidized polyacrylonitrile fibers 5 have a density between 1.5 and 2.5 dtex.

[0027] According to one embodiment, the pre-oxidized polyacrylonitrile fibers 5 have a length between 30 and 80 mm, and in particular between 50 and 60 mm.

[0028] According to one embodiment, the foam flakes 3 have a maximum size of 20 mm.

[0029] According to one embodiment, the foam flakes 3 have a density between 35 and 55 kg / m3.

[0030] According to one embodiment, the pre-oxidized polyacrylonitrile fibers 5 are from recycling.

[0031] According to one embodiment, the two-component fibers 4 comprise a core based on polyethylene terephthalate and a sheath based on polyethylene terephthalate modified to lower its melting point.

[0032] A floor or apron assembly 2 of a motor vehicle is now described, said assembly comprising: • a panel 1 as described previously, • a covering layer 6 of said panel, for example made of carpet or plastic sheet.

[0033] Finally, a manufacturing process for such a panel 1 is described, comprising the following steps: • to produce a mattress from a mixture comprising between 65 and 85% by weight of elastically compressible polyurethane foam flakes 3, between 10 and 25% by weight of bi-component fibers 4 and between 5 and 15% by weight of pre-oxidized polyacrylonitrile (PAN) fibers 5, • place it in an oven, for example at a temperature of approximately 160°C, in order to melt the sheath of said two-component fibers, • to calcine and cool it, • cut a piece from the mattress, • to heat the said plate, in particular by contact between heating plates or in an oven, • to make a mold of said plate in a mold, so as to obtain said panel by thermo-compression.

[0034] Alternatively, it may be envisaged to fill the matrix of a mold with a mixture - comprising between 65 and 85% by weight of elastically compressible polyurethane foam flakes 3, between 10 and 25% by weight of bi-component fibers 4 and between 5 and 15% by weight of pre-oxidized polyacrylonitrile (PAN) fibers 5 -, and then to compress said mixture heated to the melting temperature of the sheath of said bi-component fibers by means of a punch, in order to obtain the expected panel 1.

Claims

Demands

1. Acoustic decoupling panel (1) intended for lining a floor or apron (2) of a motor vehicle, said panel being based on a thermo-compressed mixture comprising: • between 65 and 85% by weight of elastically compressible polyurethane foam flakes (3), • between 10 and 25% by weight of bi-component fibers (4) for bonding said flakes together, said fibers comprising a core fusible at a first temperature and a sheath fusible at a second temperature lower than said first temperature, said flakes having been bonded together by melting said sheath, said panel being characterized in that said mixture further comprises between 5 and 15% by weight of pre-oxidized polyacrylonitrile fibers (5), so as to improve its resistance to combustion.

2. Panel (1) according to claim 1, characterized in that the mixture comprises: • 70 to 80% by weight of polyurethane foam flakes (3), • 15 to 20% by weight of bi-component fibers (4), • 5 to 10% by weight of pre-oxidized polyacrylonitrile fibers (5).

3. Panel (1) according to any one of the preceding claims, characterized in that it has at least one area of ​​density less than 80 kg / m3.

4. Panel (1) according to any one of the preceding claims, characterized in that the pre-oxidized polyacrylonitrile fibers (5) have a count between 1.5 and 2.5 dtex.

5. Panel (1) according to any one of the preceding claims, characterized in that the pre-oxidized polyacrylonitrile fibers (5) have a length between 30 and 80 mm.

6. Panel (1) according to any one of the preceding claims, characterized in that the foam flakes (3) have a maximum size of 20 mm.

7. Panel (1) according to any one of the preceding claims, characterized in that the foam flakes (3) have a density between 35 and 55 kg / m3.

8. Panel (1) according to any one of the preceding claims, characterized in that the two-component fibers (4) comprise a core based on polyethylene terephthalate and a sheath based on polyethylene terephthalate modified to lower its melting point.

9. Motor vehicle floor or apron trim assembly (2), said assembly comprising: • a panel (1) according to any one of the preceding claims, • a covering layer (6) of said panel.

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