Acoustic protection panel for motor vehicles

Abstract

The invention relates to a soundproof panel (1) for motor vehicles, said panel comprising, arranged successively one on top of the other, a porous, heat-conformable sound-absorbing layer (2), a thermoplastic sealing film (3), and an elastically compressible spring layer (4), said panel further comprising a porous granular layer (5) based on ground hot-melt material, said granular layer being bonded between said porous layer and said film, said porous layer having a compressive Young's modulus greater than 1 MPa, so as to also provide a stiffening function. Figure 1

Description

Title of the invention: Acoustic protection panel for a motor vehicle

[0001] The invention relates to an acoustic protection panel for a motor vehicle and a method for producing such a panel.

[0002] It is known to produce an acoustic protection panel for a motor vehicle, said panel comprising, arranged successively one on top of the other:

[0003] • a porous heat-formable acoustic absorption layer,

[0004] • a thermoplastic sealing film, • a layer of elastically compressible spring,

[0005] so that said panel allows acoustic insulation according to a “mass / spring” principle, the mass being formed by said porous layer associated with said film and the spring by said spring layer, said panel furthermore having acoustic absorption properties provided by said porous layer.

[0006] When it is said that the porous layer is heat conformable, it is meant that it can adopt an appropriate geometry once heated to a sufficient temperature and shaped in a mold.

[0007] Due to the insulation and absorption characteristics provided by this type of panel, potential applications include the production of apron panels on the passenger compartment or engine side, passenger compartment under-carpet or even luggage compartment.

[0008] Since the film has a very low surface mass, it is necessary to give the porous layer a high surface mass in order to optimize the acoustic insulation performance.

[0009] But we are often conditioned by the fact that the porous layer must have a minimized thickness, which requires it to be overcompressed, and therefore over-densified.

[0010] As a result, the porosity of the porous layer is reduced, and its resistance to the passage of air is drastically increased, which is detrimental to its sound absorption properties.

[0011] Faced with these drawbacks, the invention aims in particular to propose a panel making it possible to preserve / improve acoustic insulation, without harming its acoustic absorption properties and without generating significant excess thickness.

[0012] To this end, and according to a first aspect, the invention proposes an acoustic protection panel for a motor vehicle, said panel comprising, arranged successively one on top of the other:

[0013] • a porous heat-formable acoustic absorption layer,

[0014] • a thermoplastic sealing film, • a layer of elastically compressible spring,

[0015] said panel further having the following characteristics:

[0016] • it further comprises a porous granular layer, based on ground thermofusible material, said granular layer being associated between said porous layer and said film,

[0017] • said porous layer has a Young's modulus in compression greater than 1 MPa, so as to also provide a stiffening function.

[0018] With such an arrangement, the mass of the “mass / spring” system is formed by the film / granular layer / porous layer stack.

[0019] The proposed arrangement allows in particular:

[0020] • to increase the mass added above the spring layer, and this without harming the absorption properties provided by the porous layer and without any significant impact on the increase in thickness of the panel insofar as the material constituting the ground material is chosen to be sufficiently dense, the excess thickness being provided solely by the granular layer, • to be able to deposit, if necessary, a very low surface mass of crushed material, due to its granular nature which allows in particular light dusting; in addition, it is possible, as we will see later, to provide for the granular layer zones of differentiated surface mass obtained by differentiated dusting, • to give the granular layer a behavior similar to that of a non-granular waterproof layer, said granular layer behaving like a waterproof layer thanks to the significant stiffness given to the porous layer which generates with the film a “mass gain” effect of the multilayers placed above the spring layer, • to obtain, due to the thermofusible nature of the granular layer, by heating said layer during the manufacture of the panel, cohesion between said granular layer and the porous layer and between said granular layer and the film, which is essential to ensure good acoustic insulation, • to provide a porous layer of moderate surface mass, which makes it possible to shorten its heating time before its conformation and also to avoid its saturation in resistance to the passage of air, • to use shredded material made from recycled material, which is good for the environment.

[0021] According to a second aspect, the invention proposes a method for producing such an element.

[0022] Other features and advantages of the invention will appear in the description which follows, made with reference to the attached figures, in which:

[0023] [Fig.l] is a schematic view in partial section of a panel according to one embodiment,

[0024] [Fig.2] is a presentation of the sound absorption coefficient of a panel as a function of frequency (in Hz), for:

[0025] • a reference panel (curve 1): layer of flexible spring with a density equal to 65 kg / m3 and a thickness equal to 17 mm; film with a surface mass equal to 80 g / m2; compressed felt with a surface mass equal to 3000 g / m2 and a thickness equal to 8 mm, • a panel according to an embodiment of the invention (curve 2): flexible spring layer with a density equal to 65 kg / m3 and a thickness equal to 16 mm; film with a surface mass equal to 80 g / m2; granular layer with a surface mass equal to 1500 g / m2 and a thickness equal to 1 mm; compressed felt with a surface mass equal to 1500 g / m2 and a thickness equal to 8 mm,

[0026] [Fig.3] is a presentation of the sound reduction index (or "transmission loss", in dB) of a panel as a function of the frequency (in Hz), for the reference panel (curve 1) and the panel according to the invention (curve 2) described above.

[0027] We will now describe, with reference to the figures, an acoustic protection panel 1 for a motor vehicle, said panel comprising, arranged successively one on top of the other:

[0028] • a porous heat-formable acoustic absorption layer 2,

[0029] • a thermoplastic sealing film 3, • an elastically compressible spring layer 4,

[0030] said panel further having the following characteristics:

[0031] • it further comprises a porous granular layer 5, based on ground thermofusible material, said granular layer being associated between said porous layer and said film, • said porous layer has a Young's modulus in compression greater than 1 MPa, so as to also provide a stiffening function.

[0032] According to one embodiment, the porous layer 2 has a Young's modulus in compression of between 10 and 100 MPa, making it possible to guarantee the “mass-spring” behavior without resonance over the entire frequency spectrum up to 10 kHz, this typically for a thickness of said layer of between 3 and 10 mm.

[0033] According to one embodiment, the ground material has a Young's modulus in compression of between 100 and 800 MPa, which makes it possible to limit the resonance phenomena of the porous layer 2 in the frequency spectrum up to 10 kHz.

[0034] According to one embodiment, the spring layer 4 is fixed to the film 3, for example by gluing or by overmolding said film with said layer.

[0035] According to another embodiment, there is no connection between the spring layer 4 and the film 3, the porous layer 2 / granular layer 5 / film 3 assembly being placed on said spring layer.

[0036] According to one embodiment, the porous layer 2 has a resistance to the passage of air of less than 3000 Nsm3.

[0037] According to one embodiment, the porous layer 2 is based on fibrous material with a surface mass greater than 600 g / m2, and in particular between 1200 and 1500 g / m2.

[0038] In particular, the fibrous material is based on structural fibers - for example polyester - bonded together by a bonding agent - for example formed by two-component bonding fibers comprising a core, fusible at high temperature, and a sheath fusible at lower temperature, said core being in particular based on polyester and said sheath based on modified polyester.

[0039] According to another embodiment, the porous layer 2 is based on elastically compressible foam flakes - in particular polyurethane - and two-component bonding fibers comprising a core, fusible at high temperature, and a sheath fusible at lower temperature - said core being in particular based on polyester and said sheath based on modified polyester -, said fibers occupying between 10 and 30% by mass of said layer and said flakes between 90 and 70%.

[0040] According to one embodiment, the porous layer 2 based on foam flakes and connecting fibers has a surface mass of between 1200 and 1500 g / m2.

[0041] According to one embodiment, the granular layer 5 has a porosity - that is to say a void rate relative to the overall volume - of between 5 and 20%.

[0042] According to one embodiment, the material constituting the granular layer 5 has a density of between 1500 and 2500 kg / m3.

[0043] According to one embodiment, the granular layer 5 has a surface mass of between 500 and 3000 g / m2.

[0044] According to one embodiment, the granular layer 5 is based on recycled material.

[0045] According to various embodiments, the granular layer 5 is optionally based on:

[0046] • recycled automotive carpet shredder, said shredder comprising particles of thermoplastic elastomer material - for example ethylene propylene diene monomer - loaded with a mineral filler - for example barite - and fibers - for example polyester -, • or polyvinyl butyral (PVB).

[0047] A classic use of PVB consists of interposing it as a film between two layers of glass, in particular to make windshields for motor vehicles or windows for buildings.

[0048] A characteristic of this material is its very high elasticity which allows it to retain broken glass and prevents the layers of glass from shattering upon impact.

[0049] Such elasticity makes it possible to envisage its thermoforming with strong stretching and without breaks.

[0050] Furthermore, PVB has the particularity of having a density of the order of 1.1, much higher than that of the shredded materials conventionally used, which makes it possible to have a granular layer 5 of smaller volume, and therefore to optimize the volume available elsewhere in the vehicle.

[0051] Finally, due to its highly sticky nature, the PVB exhibits very strong adhesion to the film 3 and the porous layer 2.

[0052] According to one embodiment, the size of the particles of granular material is between 1 and 6 mm.

[0053] According to various embodiments, the film 3 is based on polyamide and / or polyester, so as not to melt during the hot shaping of the panel 1.

[0054] According to one embodiment, the film 3 is composed of several layers of different thermoplastic materials, for example consisting of a layer of polyamide taken between two layers of polyethylene.

[0055] According to one embodiment, the film 3 has a thickness of between 25 and 150 microns.

[0056] According to various embodiments, the spring layer 4 is optionally based on:

[0057] • of fibrous material, having in particular a surface mass of between 600 and 1800 g / m2, • or molded foam - in particular polyurethane - overmolding the film 3, having in particular a density of between 40 and 80 kg / m3, • or elastically compressible foam flakes - in particular polyurethane - and two-component bonding fibers comprising a core, fusible at high temperature, and a sheath fusible at lower temperature, said fibers occupying between 10 and 30% by mass of said layer and said flakes between 90 and 70%, the whole having in particular a surface mass of between 600 and 1800 g / m2.

[0058] According to one embodiment, the spring layer 4 has a Young's modulus in compression of between 5 and 90 KPa.

[0059] According to one embodiment, in the case of a spring layer 4 based on foam flakes bonded by two-component fibers, it can be provided that said layer comes from a molding allowing it to be given a three-dimensional geometry with controlled density.

[0060] According to various embodiments, the panel 1 has a heavy zone 6 where the granular layer 5 has a high surface mass, so as to achieve high acoustic insulation, and a light zone 7, with less acoustic insulation, having one or other of the following characteristics:

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[0071] • said granular layer is thinned, according to the embodiment shown, so as to have a lower surface mass, • said granular layer is removed, according to a variant not shown, the porous layer 2 being directly associated with the sealing film 3. As will be seen later, the granular layer 5 can be deposited by sprinkling. Knowing that panel 1 is generally placed opposite a heterogeneous surface in sound emission, it is necessary, in order to ensure adequate acoustic protection, to deposit a quantity of crushed material taking into account the most emissive portion of the surface. This results in a panel 1 of significant mass contributing to making the vehicle heavier, which is detrimental in terms of fuel consumption. This is why it is relevant to consider a differentiated sprinkling of the crushed material to achieve just the necessary insulation and lighten panel 1. Finally, a method for producing such a panel 1 is described, said method comprising the following steps: • provide shredded material, particularly from recycling, • provide a porous layer 2 and a thermoplastic film 3, • depositing said ground material by sprinkling between said porous layer and said film, said layer and said film being in particular in the form of rollers operated in continuous unwinding or in the form of plates, • calender the assembly with said ground material brought to softening temperature so as to produce a complex, • hot conform in a cooled mold a plate of said complex to the geometry of panel 1 to be obtained, • associate a layer of spring 4 with said plate once shaped. According to various embodiments, the association of the spring layer 4 with the complex plate can be carried out: • either during the hot shaping step, said spring layer being superimposed on the film 3 during said step, • either in a delayed step, in particular by gluing, or by overmolding when said spring layer is based on molded foam. In the case of a deferred association and an overmolded spring layer 4, it is possible to provide for hot conforming of the plate according to a three-dimensional geometry before its overmolding. According to one embodiment, the crushed material is deposited in a differentiated manner, as explained above, so as to produce a panel 1 provided with a heavy zone 6, with high acoustic insulation, and a light zone 7, with less acoustic insulation.

[0072] We now comment on the curves in Figures 2 and 3.

[0073] It can be seen in [Fig. 3] that the insulation performance of a panel according to the invention is very similar to that of a reference panel whose complex (porous layer / film) placed above the spring layer has the same total surface mass of 3000 g / m2.

[0074] On the other hand, it is observed, in [Fig. 2], that the absorption properties in diffuse field (for a flat sample of 1.2 m2) of a panel according to the invention are much superior to those of the reference panel mentioned above above approximately 1000 Hz (improvement of 10 to 15%), knowing however that the saturation of the resistance to the passage of air linked to the overcompression of the porous layer in the reference panel has a slight beneficial effect (of the order of 5%) at medium frequencies (400-1000 Hz).

Claims

Claims

1. Acoustic protection panel (1) for a motor vehicle, said panel comprising, arranged successively one on top of the other: • a porous heat-conformable acoustic absorption layer (2), • a thermoplastic sealing film (3), • an elastically compressible spring layer (4), said panel being characterized in that: • it further comprises a porous granular layer (5), based on ground thermofusible material, said granular layer being associated between said porous layer and said film, • said porous layer has a Young's modulus in compression greater than 1 MPa, so as to also provide a stiffening function.

2. Panel according to claim 1, characterized in that the porous layer (2) has a Young's modulus in compression of between 10 and 100 MPa.

3. Panel according to one of the preceding claims, characterized in that the ground material has a Young's modulus in compression of between 100 and 800 MPa.

4. Panel according to any one of claims 1 to 3, characterized in that the porous layer (2) has a resistance to the passage of air of less than 3000 Nsm3.

5. Panel according to any one of claims 1 to 4, characterized in that the porous layer (2) is based on fibrous material with a surface mass greater than 600 g / m2.

6. Panel according to any one of claims 1 to 4, characterized in that the porous layer (2) is based on elastically compressible foam flakes and two-component bonding fibers comprising a core, fusible at high temperature, and a sheath fusible at lower temperature, said fibers occupying between 10 and 30% by mass of said layer and said flakes between 90 and 70%.

7. Panel according to any one of the preceding claims, characterized in that the material constituting the granular layer (5) has a density of between 1500 and 2500 kg / m3.

8. Panel according to any one of the preceding claims, characterized in that the granular layer (5) is based on: • recycled automobile carpet shredder, said shredder comprising particles of thermoplastic elastomer material loaded with a mineral filler and fibers, • or polyvinyl butyral.

9. Panel according to any one of the preceding claims, characterized in that the spring layer (4) is optionally based on: • fibrous material, • or molded foam overmolding the film (3), • or elastically compressible foam flakes and two-component bonding fibers comprising a core, fusible at high temperature, and a sheath fusible at lower temperature, said fibers occupying between 10 and 30% by mass of said layer and said flakes between 90 and 70%.

10. Panel according to any one of the preceding claims, characterized in that it has a heavy zone (6) where the granular layer (5) has a high surface mass and a lightened zone (7) having either one or other of the following characteristics: • said granular layer is thinned so as to have a lower surface mass, • said granular layer is removed, the porous layer (2) being directly associated with the sealing film (3).

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