Acoustic decoupling panel

Abstract

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

Description

[0001] DESCRIPTION

[0002] Acoustic decoupling panel

[0003] 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.

[0004] It is known to produce an acoustic decoupling panel intended for use on the floor or apron of a motor vehicle, said panel being based on a thermo-compressed mixture comprising:

[0005] • between 65 and 85% by weight of elastically compressible polyurethane foam flakes,

[0006] • 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.

[0007] 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 the panel with a density of less than approximately 80 kg / m³ 3 .

[0008] The fact that areas of low density are so combustible is explained a priori by the large quantity of air they contain, which is conducive to combustion.

[0009] This results in the need to produce a panel of significant mass to meet combustibility requirements, which is detrimental to the desired weight reduction for motor vehicles.

[0010] The invention aims to overcome this drawback. 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:

[0011] • between 65 and 85% by weight of elastically compressible polyurethane foam flakes,

[0012] • 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, said panel mixture further comprising between 5 and 15% by weight of pre-oxidized polyacrylonitrile (PAN) fibers, so as to improve its resistance to combustion.

[0013] 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.

[0014] Such a partial pyrolysis operation causes a break in the molecular chains of polyacrylonitrile and the formation of cyclic structures.

[0015] It should be noted that pre-oxidized polyacrylonitrile fibers are known to constitute intermediate fibers in the production of carbon fibers from further pyrolysis.

[0016] With the proposed arrangement, a noticeable 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. 3 .

[0017] This results in the possibility of obtaining a lightweight panel with combustion resistance that meets the requirements of the automotive industry. 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:

[0018] • 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,

[0019] • 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.

[0020] 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.

[0021] In other aspects, the invention proposes a trim assembly comprising such a panel.

[0022] Other features and advantages of the invention will become apparent in the following description, made with reference to the attached figure:

[0023] [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.

[0024] We first describe an acoustic decoupling panel 1 intended to line a floor - in particular a passenger compartment or trunk - or a firewall 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,

[0025] • 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 mixture further comprising between 5 and 15% by weight of pre-oxidized polyacrylonitrile (PAN) fibers 5, so as to improve its resistance to combustion.

[0026] In particular, the mixture includes:

[0027] • 70 to 80% by weight of polyurethane foam flakes,

[0028] • 15 to 20% by weight of bi-component fibers 4,

[0029] • 5 to 10% by weight of pre-oxidized polyacrylonitrile fibers 5.

[0030] According to one embodiment, panel 1 has at least one area with a density less than 80 kg / m³ 3 - and in particular between 50 and 60 kg / m 3 - said zone exhibiting the expected resistance to combustion despite its low density.

[0031] According to one implementation, the area(s) with a density less than 80 kg / m³ 3 extend over at least 30% of the surface of panel 1.

[0032] Flame propagation speed measurements carried out - according to the ISO 3795 standard in force at the date of the 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:

[0033] • reference test specimen (density: 80 kg / m³) 3 ): 99 mm / minute,

[0034] • test tube according to the invention (density: 50 kg / m³) 3 ): 84 mm / minute. It is observed that the addition of pre-oxidized fibers in the composition of panel 1 makes it possible to obtain a notable improvement in its resistance to combustion while allowing its weight to be drastically reduced.

[0035] According to one realization, pre-oxidized polyacrylonitrile fibers 5 have a count between 1.5 and 2.5 dtex.

[0036] 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.

[0037] According to one design, the 3 foam flakes have a maximum size of 20 mm.

[0038] According to one experiment, the foam flakes 3 have a density between 35 and 55 kg / m³ 3 .

[0039] According to one design, the pre-oxidized polyacrylonitrile fibers 5 are sourced from recycling.

[0040] 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.

[0041] We are now describing a set of floor or apron trim 2 for a motor vehicle, said set comprising:

[0042] • a panel 1 as described previously,

[0043] • a covering layer 6 of said panel, for example made of carpet or plastic sheet.

[0044] Finally, a manufacturing process for such a panel 1 is described, comprising the following steps:

[0045] • 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,

[0046] • 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,

[0047] • to calcine and cool it,

[0048] • cut a plate from the said mattress,

[0049] • to heat the said plate, in particular by contact between heating plates or in an oven,

[0050] • to make a mold of said plate in a mold, so as to obtain said panel by thermo-compression.

[0051] 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

7 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 flakes (3) of elastically compressible polyurethane foam, • 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 with a density of less than 80 kg / m³ 3 .

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. 8 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 of between 35 and 55 kg / m³ 3 .

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. Floor or apron trim assembly (2) of a motor vehicle, said assembly comprising: • a panel (1) according to any one of the preceding claims, • a cladding layer (6) of said panel.

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