Acoustic-protection screen

Abstract

The invention relates to an acoustic-protection screen (1) intended to be mounted under a motor vehicle, said screen comprising a thermoformed shell (2) comprising: between 10% and 50% of mineral structural fibers, between 30% and 50% of binding fibers and between 15% and 25% by weight of polyethylene terephthalate (PET)-based sound-absorbing fibers with a count of between 1.5 and 2 dtex, said screen further comprising a protective fibrous layer (4) covering said outer face, said layer comprising between 30 and 50% by weight of bi-component fibers and between 70 and 50% of polyethylene terephthalate (PET) fibers with a count of between 6 and 7 dtex.

Description

[0001] DESCRIPTION

[0002] Title: Acoustic protection screen

[0003] The invention relates to an acoustic protection screen intended to be mounted under a motor vehicle.

[0004] There is known, in particular from document EP-3 994 679, an acoustic protection screen intended to be mounted under a motor vehicle, said screen comprising a thermoformed shell, said shell being based on structural fibers bonded together by a heat-activated bonding agent, said shell being provided with an external face intended to be turned towards the road, said shell comprising:

[0005] • between 10% and 50% of mineral structural fibers, particularly glass, to provide mechanical strength,

[0006] • between 30% and 50% of polypropylene fibers forming the bonding agent between the fibers following their fusion,

[0007] • between 15% and 25% by weight of sound absorption fibers based on polyethylene terephthalate (PET), with a count between 1.5 and 2 dtex.

[0008] Such a screen has the advantage, due to the porosity of the hull, of allowing acoustic absorption of the noise emitted by the engine, and this is all the more so since fine fibers are integrated to accentuate this absorption.

[0009] Furthermore, it has very good mechanical strength provided by the presence of mineral fibers.

[0010] However, such a screen is very fragile when faced with the projection of gravel, as the mineral fibres are very brittle.

[0011] To overcome this drawback, it has been proposed to cover the face exposed to projections with a plastic film or a coating of plastic material. However, the application of such a film or coating leads to a degradation of the absorption properties, this to the extent that said film creates a sealing barrier on the screen preventing the propagation of acoustic waves within it to be absorbed there.

[0012] The invention aims to overcome these drawbacks by proposing a screen which is both highly robust against the projection of gravel, whilst also offering good performance in terms of mechanical strength and acoustic absorption.

[0013] To this end, the invention proposes an acoustic protection screen intended to be mounted under a motor vehicle, said screen comprising a thermoformed shell, said shell being based on structural fibers bonded together by a heat-activated bonding agent, said shell being provided with an external face intended to be turned towards the road, said shell comprising: o between 10% and 50% of mineral structural fibers to provide mechanical strength, o between 30% and 50% of bonding fibers, forming said bonding agent, allowing the bonding of the different constituent fibers of said shell together, o between 15% and 25% by weight of sound-absorbing fibers based on polyethylene terephthalate (PET), with a count of between 1.5 and 2 dtex, said screen further comprising a fibrous layer for protection against the projection of gravel covering said external face,said layer comprising: o between 30 and 50% by weight of bi-component fibers comprising a high-temperature fusible core and a lower-temperature fusible sheath, said sheath having been brought to its melting point, o between 70 and 50% of polyethylene terephthalate (PET) fibers with a count of between 6 and 7 dtex. With such an arrangement, as will be seen in detail later, a screen is provided which is both highly robust against the projection of gravel, while also offering good performance in terms of mechanical strength and acoustic absorption.,

[0014] It should be noted here that the presence of high-density polyethylene terephthalate (PET) fibres - namely between 6 and 7 dtex - in the protective layer contributes to the mechanical strength of the screen.

[0015] Other features and advantages of the invention will appear in the following description, given with reference to the attached figures, in which:

[0016] [Fig.1] is a schematic view in partial section of a screen according to one embodiment,

[0017] [Fig.2] is a graphical representation of the acoustic absorption performance (alpha coefficient on the ordinate) as a function of the 1 / 3 octave frequency in Hertz, in a diffuse field, of a sample from a screen (B) according to the invention (solid curve) and of another sample (A) from a reference screen (dotted curve) according to the prior art (the characteristics of which are presented below).

[0018] An acoustic protection screen 1 is now described, intended to be mounted under a motor vehicle, said screen comprising a thermoformed shell 2, said shell being based on structural fibers bonded together by a heat-activated bonding agent, said shell being provided with an external face 3 intended to be turned towards the road, said shell comprising: o between 10% and 50% of mineral structural fibers - in particular glass - to provide mechanical strength, o between 30% and 50% of bonding fibers, forming said bonding agent, allowing the bonding of the different constituent fibers of said shell together, o between 15% and 25% by weight of sound-absorbing fibers based on polyethylene terephthalate (PET), with a count of between 1.5 and 2 dtex, said screen further comprising a protective fibrous layer 4 against the projection of gravel covering said external face,said layer comprising: o between 30 and 50% by weight of bi-component fibers comprising a high-temperature fusible core and a lower-temperature fusible sheath, said sheath having been brought to its melting point, o between 70 and 50% of polyethylene terephthalate (PET) fibers with a count of between 6 and 7 dtex.,

[0019] According to one embodiment, the connecting fibers of the shell 2 are formed by polypropylene fibers which have been brought to their melting point.

[0020] According to another embodiment, the connecting fibers of the shell 2 are formed by two-component fibers comprising a high-temperature fusible core and a lower-temperature fusible sheath, said sheath having been brought to its melting point.

[0021] In particular, the two-component fibers, both those of the shell 2 and those of the protective layer 4, may comprise a core of polyethylene terephthalate (PET), with a melting point of the order of 250°C, the sheath being of polyethylene terephthalate (PET) having undergone a chemical modification so as to have a lowered melting point, for example of the order of 180°C.

[0022] According to one embodiment, the polyethylene terephthalate (PET) fibers of the protective layer 4 may be provided with a fire-resistant treatment, in particular based on boron.

[0023] According to one embodiment, the shell 2 has a surface mass of between 800 and 1200 g / m 2 .

[0024] According to one embodiment, the shell 2 is needled so as to reinforce its mechanical strength. According to the embodiment shown, the screen 1 further comprises an internal layer 5 of non-woven intended to contain the structural fibers of the shell 2.

[0025] The presence of the internal layer 5 can also help to limit fouling of the thermoforming line, particularly when the connecting fibers are made of polypropylene.

[0026] In addition, the inner layer 5 helps protect manufacturing operators from skin and bronchial irritations that could be caused by mineral fibers.

[0027] According to one embodiment, the internal layer 5 is co-needled with the shell 2, so as to reinforce the mechanical strength of the screen 1.

[0028] Alternatively, the internal layer 5 is simply bonded to the shell 2 by the heat used during thermoforming, said layer having been provided with a coating, for example phenolic or thermoplastic, to promote bonding.

[0029] According to one embodiment, the internal layer 5 has a surface mass of between 15 and 120 g / m 2 .

[0030] According to one embodiment, the fibers of the internal layer 5 are provided with a fire-resistant treatment, for example based on boron.

[0031] According to one embodiment, the fibers of the inner layer 5 are provided with a hydro-oleophobic treatment.

[0032] According to one embodiment, the protective layer 4 has a surface mass of between 200 and 400 g / m 2 .

[0033] According to one embodiment, the protective layer 4 is co-needled with the shell 2 so as to reinforce the mechanical strength of the screen 1. A method of manufacturing such a screen 1 is described, said method comprising the following steps:

[0034] • stack, on top of each other, different fibrous layers intended to form the protective layer 4, the shell 2 and possibly the internal layer 5,

[0035] • place the assembly between two hot plates in a “contact heating” type oven, for example between 200 and 230°C,

[0036] • transfer the assembly once heated into a cold-regulated “punch / matrix” type mold, for example between 10 and 20°C,

[0037] • unmold after making any cuts in the mold or unmold before making the cuts, in particular by pressing blades or by water jet.

[0038] The sample according to the invention B which was tested has a surface mass of 1400 g / m 2 , said mass being distributed as follows:

[0039] • hull 2 ​​has a surface mass of 1000 g / m 2

[0040] • protective layer 4 has a surface mass of 300 g / m 2 ,

[0041] • the inner layer 5 has a surface mass of 100 g / m 2 .

[0042] Reference sample A is similar to sample B according to the invention, the protective layer 4 having been removed and the shell 2 made heavier by 1300 g / m 2 in order to compare two screens with the same surface mass.

[0043] In addition, a reference sample A of the same thickness (4 mm) as that of the sample according to the invention B is provided.

[0044] The comparison was made according to three criteria:

[0045] • mechanical resistance, measured by Young’s modulus,

[0046] • resistance to gravel projection (see test description below),

[0047] • sound absorption properties. The results obtained are presented in the table below.

[0048] [Table 1]

[0049] The mechanical resistance test shows that the sample according to the invention B has a slightly reduced mechanical resistance compared to that of the reference sample A, but compatible with the resistance requirements in force for a screen intended to be mounted under a motor vehicle.

[0050] The test of resistance to gravel projection (also called “resistance to shot blasting”) was carried out using the protocol described below.

[0051] The principle is to bombard the sample to be tested with cast steel shot through a nozzle.

[0052] Shot peening resistance is characterized by the time required to pierce the sample.

[0053] The chipping resistance test shows that the sample according to the invention B has a much higher chipping resistance than the reference sample A.

[0054] The sound absorption test (figure 2) shows similar absorption properties for the samples according to the invention B and reference A. Ultimately, the screen according to the invention B has both great robustness against shot blasting, while having little degradation in mechanical strength compared to that of the reference sample A and sound absorption comparable to that of said reference sample.

Claims

CLAIMS 1. Acoustic protection screen (1) intended to be mounted under a motor vehicle, said screen comprising a thermoformed shell (2), said shell being based on structural fibers bonded together by a heat-activated bonding agent, said shell being provided with an external face (3) intended to be turned towards the road, said shell comprising: o between 10% and 50% of mineral structural fibers to provide mechanical strength, o between 30% and 50% of bonding fibers, forming said bonding agent, allowing the bonding of the different constituent fibers of said shell together, o between 15% and 25% by weight of sound-absorbing fibers based on polyethylene terephthalate (PET), with a count of between 1.5 and 2 dtex, said screen being characterized in that it further comprises a protective fibrous layer (4) against the projection of gravel covering said external face,said layer comprising: o between 30 and 50% by weight of bi-component fibers comprising a high-temperature fusible core and a lower-temperature fusible sheath, said sheath having been brought to its melting point, o between 70 and 50% of polyethylene terephthalate (PET) fibers with a count of between 6 and 7 dtex., 2. Screen (1) according to claim 1, characterized in that the connecting fibers of the shell (2) are formed by polypropylene fibers having been brought to their melting point.

3. Screen (1) according to claim 1, characterized in that the connecting fibers of the shell (2) are formed by two-component fibers comprising a high-temperature fusible core and a lower-temperature fusible sheath, said sheath having been brought to its melting point.

4. Screen (1) according to any one of the preceding claims, characterized in that the shell (2) has a surface mass of between 800 and 1200 g / m2 .

5. Screen (1) according to any one of the preceding claims, characterized in that the shell (2) is needled.

6. Screen (1) according to any one of the preceding claims, characterized in that it further comprises an internal layer (5) of non-woven fabric intended to contain the structural fibers of the shell (2).

7. Screen (1) according to the preceding claim, characterized in that the internal layer (5) is co-needled with the shell (2).

8. Screen (1) according to one of claims 6 or 7, characterized in that the internal layer (5) has a surface mass of between 15 and 120 g / m 2 .

9. Screen (1) according to any one of the preceding claims, characterized in that the protective layer (4) has a surface mass of between 200 and 400 g / m 2 .

10. Screen (1) according to any one of the preceding claims, characterized in that the protective layer (4) is co-needled with the shell

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