Method for producing a protective sound panel for a motor vehicle

A method for producing a protective sound panel for a motor vehicle, the method comprising the following steps:

• producing a complex comprising a fibre-based reverse porous layer, a recycled material shred-based intermediate layer and a porous face layer, the complex comprising a thermoplastic binding agent,
• heating the complex to melting point of the binding agent,
• arranging the complex once heated in a thermoforming mould so as to produce a three-dimensional shell,
• after cooling, demoulding the shell,
• arranging the shell in a reaction injection moulding (RIM) mould defining a moulding cavity, the reverse layer being turned towards the cavity, a space being left vacant between the reverse layer and a wall of the cavity,
• injecting into the space a precursory foam mixture of polyurethane, elastically compressible, such that the foam overmoulds the reverse layer by penetrating it at least partially, and by penetrating the intermediate layer, so as to form a sealed sound insulation barrier,
• after expansion of the foam in the space, so as to form a spring layer, demoulding the panel obtained,
• wherein the binding agent is incorporated to the face layer, the face layer having on the panel a surface mass of between 500 and 2000 g/m2, the thermoforming of the complex being achieved such that the face layer further has:
• at least one slightly compressed zone of high absorption, so as to give the face layer sound absorption properties, the minimum total percentage of the slightly compressed zone being 40% of the surface area of the face layer, the zone having a thickness of between 4 and 10 mm, the thickness being measured according to the standard NF EN ISO 5084 with a presser foot of surface area 2000+/−20 mm2 under a pressure of 1+/−0.1 kPa,
• possibly at least one highly compressed zone of low absorption, the zone having a thickness of between 1 and 3 mm, the thickness being measured according to the standard NF EN ISO 5084 with a presser foot of surface area 2000+/−20 mm2 under a pressure of 1+/−0.1 kPa.