Method for manufacturing an acoustic protection panel for a motor vehicle

Abstract

The invention relates to a method for producing a soundproof panel (1) for motor vehicles comprising a decoupling layer based on foam flakes (3) bonded together by a heat-activated bonding agent (4), said bonding agent being formed by binding fibers, said fibers comprising a high-temperature fusible core and a lower-temperature fusible sheath, said flakes being bonded together by melting said sheath, so that said layer is in the form of foam flakes bonded together by said fibers, said flakes occupying between 80% and 90% by weight of said layer, so that said fibers occupy between 20% and 10% by weight of said layer. Figure 2

Description

Title of the invention: Method for producing an acoustic protection panel for a motor vehicle

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

[0002] It is known to implement a method for producing an acoustic protection panel for a motor vehicle, said panel comprising an elastically compressible acoustic decoupling layer, said layer being based on a mixture of fibers bonded by a heat-activatable bonding agent, said method comprising the following steps: • provide a mold allowing the successive definition of a first cavity and a second cavity of smaller volume, • pre-compress said mixture in said first cavity and heat it so as to activate said agent and confer a pre-geometry to said mixture, • while maintaining heating, define said second molding cavity so as to overcompress said mixture to obtain said decoupling layer, • cool said layer and remove it from said mold.

[0003] The known method involves an essentially fibrous decoupling layer, the bonding agent being formed in particular by fusible fibers.

[0004] A panel thus produced can in particular be placed on the floor or on the apron of the vehicle, that is to say the metal wall separating the engine compartment from the passenger compartment.

[0005] Such a panel may comprise, in addition to the decoupling layer, a waterproof mass layer associated with said decoupling layer to form, due to the elasticity of said decoupling layer, a “mass-spring” system having acoustic insulation properties.

[0006] According to another embodiment, the panel may comprise, in addition to the decoupling layer, a porous layer associated with said decoupling layer so as to form a “bi-permeable” absorbent system.

[0007] We will see later on methods of implementing such systems within the framework of the invention.

[0008] The method described above makes it possible to produce a three-dimensional panel in which the density of the decoupling layer can be controlled in any zone depending on the expected load-bearing and / or acoustic behavior properties.

[0009] For example, one can provide an area - such as a "foot cellar" or a zone of crankset - featuring increased density and lift and another area of ​​lower density.

[0010] However, with such a method, it is difficult to give the decoupling layer a precise geometry, in particular in a radiated zone of small radius - in particular less than 10 mm -, except at the cost of drastic overcompression in said zone where said layer becomes very compact and loses its acoustic decoupling properties.

[0011] Such behavior could be explained by the essentially fibrous nature of the decoupling layer, the linear nature of the fibers and their significant length - for example between 40 and 100 mm - forming an obstacle to the definition of fine geometric shapes on said layer.

[0012] The result is that the decoupling layer, once mounted on its support (in particular a sheet metal): • either does not closely match the shape of said support in the areas of fine geometry, resulting in degraded damping properties, due to the absence of damping induced in the absence of contact between said layer and said support, • either is in contact with said support in said areas, but does not present the expected acoustic decoupling properties due to its overcompression (Young's modulus too high).

[0013] The aim of the invention is to propose a method making it possible to overcome these drawbacks.

[0014] To this end, the invention proposes a method for producing an acoustic protection panel for a motor vehicle, said panel comprising an elastically compressible acoustic decoupling layer, said layer being based on elastically compressible foam flakes agglomerated together by a heat-activatable bonding agent, said method comprising the following steps: • provide a mold provided with a matrix, said mold making it possible to successively define a first cavity and a second cavity of smaller volume, • provide a homogeneous mixture of said flakes and said binding agent, • arrange said mixture in said matrix so as to form a mattress, • place a first punch opposite said die so as to define a first molding cavity providing pre-compression of said mattress, • heating said pre-compressed mattress to the activation temperature of said agent so as to ensure pre-maintenance of said flakes between them, • place a second punch opposite said die so as to define a second molding cavity allowing said die to be overcompressed mattress to obtain said decoupling layer, • cool said layer and remove it from said mold,

[0015] said method further having the following characteristics: • said binding agent is formed by binding fibers, said fibers comprising a high-temperature fusible core and a lower-temperature fusible sheath, • said flakes are bonded together by fusion of said sheath, so that said layer is in the form of foam flakes agglomerated by said fibers, • said flakes occupy between 80% and 90% by weight of said layer, so that said fibers occupy between 20% and 10% by weight of said layer.

[0016] The implementation of such a method applied to such a decoupling layer composition makes it possible, surprisingly, to finely conform the geometry of said layer while preserving its acoustic decoupling properties, including in areas of very fine geometry, for example having radii of the order of 5 mm, while maintaining a moderate density of said layer in said areas.

[0017] A judicious choice of the size of the flakes makes it possible to refine the geometric definition of the decoupling layer at will, knowing that a reduction in their size goes in the direction of an improvement in the geometric definition.

[0018] Other features and advantages of the invention will appear in the following description given with reference to the attached figures, in which:

[0019] [Fig. la],

[0020] [Fig.lb]and

[0021] [Fig. le] represent different stages of the process, in partial schematic section, according to one embodiment, [Fig.la] representing the stage of placing the mixture in the matrix to form a mattress, [Fig.lb] the pre-conformation of said mattress in the first cavity and [Fig. le] the conformation of said mattress by overcompression in the second cavity to obtain the decoupling layer,

[0022] [Fig.2] represents a panel according to one embodiment, the decoupling layer being associated with a ground layer.

[0023] [Fig.3] represents a binding fiber in schematic section.

[0024] With reference to the figures, a method for producing an acoustic protection panel 1 for a motor vehicle is described, said panel comprising an elastically compressible acoustic decoupling layer 2, said layer being based on elastically compressible foam flakes 3 - in particular from used bedding mattresses - agglomerated together by a heat-activatable bonding agent 4, said method comprising the following steps: • provide a mold provided with a matrix 5, said mold making it possible to successively define a first cavity 6 and a second cavity 7 of smaller volume, • provide a homogeneous mixture of said flakes and said binding agent, • arrange said mixture in said matrix so as to form a mattress 17, • place a first punch 12 opposite said matrix so as to to define a first molding cavity 6 providing pre-compression of said mattress, • heating said pre-compressed mattress to the activation temperature of said agent so as to ensure pre-maintenance of said flakes between them, • place a second punch 13 opposite said matrix so as to define a second molding cavity 7 making it possible to overcompress said mattress to obtain said decoupling layer, • cool said layer and remove it from said mold,

[0025] said method further having the following characteristics: • said binding agent is formed by binding fibers, said fibers comprising a core 9 which is fusible at high temperature and a sheath 10 which is fusible at lower temperature, • said flakes are bonded together by fusion of said sheath, so that said layer is in the form of foam flakes agglomerated by said fibers, • said flakes occupy between 80% and 90% by weight of said layer, so that said fibers occupy between 20% and 10% by weight of said layer.

[0026] The heating and cooling described above can be carried out in particular by a flow of air (symbolized by arrows in figures 1b and 1c) brought to the chosen temperature, here by means of orifices 11 provided for this purpose in the die 5 and the punches 12, 13.

[0027] According to another embodiment, the heating is carried out by steam sent under pressure.

[0028] According to one embodiment, the flakes 3 occupy between 83% and 87% by weight of the lower layer 2, and in particular of the order of 85%, so that the fibers 4 occupy between 17% and 13% by weight of said layer.

[0029] According to various embodiments, the flakes 3 have the following characteristics: • they are polyurethane based, • and / or their density before compression is between 15 and 80 kg / m3, • and / or 90% of said flakes have a maximum dimension before compression of between 5 and 20 mm, and in particular less than 10 mm, • and / or their Young’s modulus before compression is less than 50 kPa.

[0030] According to one embodiment, the mixture 8 is projected under pressure into the matrix 5.

[0031] According to one embodiment, the fibers 4 have a count of between 1.7 and 6.7 dtex, being notably of the order of 4.4 dtex.

[0032] The use of relatively fine fibers 4 promotes absorption by visco-thermal dissipation, which has a favorable role on the effectiveness of acoustic decoupling.

[0033] According to one embodiment, the core 9 is based on polyester and the sheath 10 is based on copolyester.

[0034] According to one embodiment, the mattress 17 is pressed against the matrix 5 by suction (symbolized by arrows in [Fig. 1a]) through orifices 11 provided in said matrix.

[0035] According to the embodiment shown, the mixture 8 is arranged in the matrix 5 in an inhomogeneous manner according to at least two zones 18a, 18b, so that the surface mass of the mattress 17 is different from one of said zones to the other.

[0036] The local density of the decoupling layer 2 obtained is a function of the compression rate achieved in each of its zones during its conformation to its final geometry in the second cavity 7.

[0037] It is possible in particular to provide an increased density in areas requiring high load-bearing capacity, such as the “foot wells” of a floor covering, while maintaining good acoustic decoupling, including for very high density masses of the decoupling layer 2, for example of the order of 300 kg / m3.

[0038] In particular, a density of between 50 and 80 kg / m3 in the low compression zone and between 100 and 200 kg / m3 in the high compression zone can be provided.

[0039] In the same way, it may be provided, in a manner not shown, to locally increase the density of the decoupling layer 2 in zones comprising orifices intended for the passage of functional members, such as the steering column, in order to guarantee good pressing of said layer against said member, and therefore good acoustic sealing.

[0040] According to the embodiment shown, the second punch 13 is formed by deformation of the first punch 12, said first punch being provided with at least one movable part 19 which can be actuated to overcompress the mattress 17 opposite said part.

[0041] According to one embodiment, illustrated in [Fig.2], the method further comprises the step of associating, for example by gluing, a mass layer 16 with the decoupling layer 2, so as to form a “mass-spring” system.

[0042] According to various embodiments, the ground layer 16, which can be located only on a part of the decoupling layer 2, is formed as desired by: • a dense waterproof layer; such a dense layer may, for example, be based on EPDM loaded with a mineral filler, such as calcium carbonate; it may in particular have a surface mass of between 1000 and 4000 g / m2; according to one embodiment, said dense layer can be coated with a porous layer, for example fibrous, intended to further provide acoustic absorption and / or an advantageous appearance, • or a waterproof film, for example with a thickness of between 50 and 150 microns, coated with a stiff porous acoustic absorption layer, for example fibrous - which may in particular have a surface mass of between 1000 and 2500 g / m2 - said porous layer contributing essentially to the mass of said mass layer.

[0043] The mass layer 16 can be shaped, prior to its association with the decoupling layer 2, to the geometry of said decoupling layer once shaped so as to closely match its geometry.

[0044] According to another embodiment not shown, the method further comprises the step of associating a porous layer permeable to air with the decoupling layer 2, so as to form a “bi-permeable” system.

[0045] The porous layer is for example a compressed felt or made up of compressed foam flakes agglomerated by binding fibers.

[0046] The porous layer may, for example, have a resistance to the passage of air of between 500 and 2500 Nsm3.

[0047] Finally, a panel 1 produced by such a method is described, said panel comprising a decoupling layer 2, said layer comprising: • 3 flakes of elastically compressible foam, • binding fibers 4, said fibers comprising a core 9 which fuses at high temperature and a sheath 10 which fuses at lower temperature,

[0048] knowing that: • said flakes are bonded together by fusion of said sheath, so that said layer is in the form of foam flakes agglomerated by said fibers, • said flakes occupy between 80% and 90% by weight of said layer, so that said fibers occupy between 20% and 10% by weight of said layer,

[0049] said decoupling layer having at least one radiated zone with a radius of between 2 and 10 mm.

[0050] According to one embodiment, the radiated zone has a Young's modulus in compression of less than 150 kPa and a density of less than 300 kg / m3.

[0051] According to one embodiment, the decoupling layer 2 has zones 18a, 18b of different densities.

Claims

Claims

1. Method for producing an acoustic protection panel (1) for a motor vehicle, said panel comprising an elastically compressible acoustic decoupling layer (2), said layer being based on elastically compressible foam flakes (3) agglomerated together by a heat-activatable bonding agent (4), said method comprising the following steps: • provide a mold provided with a matrix (5), said mold making it possible to successively define a first cavity (6) and a second cavity (7) of smaller volume, • provide a homogeneous mixture (8) of said flakes and said binding agent, • arrange said mixture in said matrix so as to form a mattress (17), • place a first punch (12) opposite said matrix so as to define a first molding cavity (6) providing pre-compression of said mattress, • heating said pre-compressed mattress to the activation temperature of said agent so as to ensure pre-maintenance of said flakes between them, • place a second punch (13) opposite said matrix so as to define a second molding cavity (7) making it possible to overcompress said mattress to obtain said decoupling layer, • cool said layer and remove it from said mold, said method further having the following characteristics: • said binding agent is formed by binding fibers, said fibers comprising a core (9) which is fusible at high temperature and a sheath (10) which is fusible at lower temperature, • said flakes are bonded together by fusion of said sheath, so that said layer is in the form of foam flakes agglomerated by said fibers, • said flakes occupy between 80% and 90% by weight of said layer, so that said fibers occupy between 20% and 10% by weight of said layer.

2. Method according to claim 1, characterized in that the flakes (3) occupy between 83% and 87% by weight of the decoupling layer (2), so that the fibers (4) occupy between 17% and 13% by weight of said layer.

3. Method according to one of the preceding claims, characterized in that the flakes (3) have the following characteristics: • they are based on polyurethane, • and / or their density before compression is between 15 and 80 g / m3, • and / or 90% of said flakes have a maximum dimension before compression of less than 10 mm, • and / or their Young's modulus before compression is less than 50 kPa.

4. Method according to any one of the preceding claims, characterized in that the mixture (8) is projected under pressure into the matrix (5).

5. Method according to any one of the preceding claims, characterized in that the mattress (17) is pressed against the matrix (5) by suction through orifices (11) provided in said matrix.

6. Method according to any one of the preceding claims, characterized in that the mixture (8) is arranged in the matrix (5) in an inhomogeneous manner in at least two zones (18a, 18b), so that the surface mass of the mattress (17) is different from one of said zones to the other.

7. Method according to any one of the preceding claims, characterized in that the second punch (13) is formed by deformation of the first punch (12), said first punch being provided with at least one movable part (19) operable to overcompress the mattress (17) opposite said part.

8. Method according to any one of the preceding claims, characterized in that it further comprises the step of associating a mass layer (16) with the decoupling layer (2), so as to form a “mass-spring” system.

9. Method according to any one of claims 1 to 7, characterized in which further comprises the step of associating a porous layer permeable to air with the decoupling layer (2), so as to form a “bi-permeable” system.

Images