Lightweight, sound-insulating lining for a body part of a motor vehicle, and method for the production thereof

(54) Title: LIGHT COVERING, SOUND INSULATION, FOR A PART OF CAR BODY OF A MOTOR VEHICLE AND PROCESS FOR ITS PRODUCTION (30) Unionist Priority: 02/05/2007 of 10 2007 020 832.6 (73) Holder (s): Bayer Materialscience AG, Carcoustics Techconsult GMBH (72) Inventor (s): Dagmar Ulbrich, DirkSoltau, Michael Hansen, Thomas Gross (74) Attorney (s): Dannemann, Siemsen, Bigler & Ipanema Moreira (86) International Request: pct EP2008054604de 16 / 04/2008 (87) International Publication: W0 2008 / i35357de 11/13/2008 (57) Abstract: lightweight, sound-insulating coating, FOR A PART OF THE BODY OF A MOTOR VEHICLE AND PROCESS FOR ITS PRODUCTION. The present invention relates to a lightweight, sound-insulating coating (1) for a body part of a motor vehicle, especially in the form of a lightweight front wall covering, comprising a layer of sound absorber (1.1), a sound-absorbing layer (1.2) essentially air-tight, directly connected with the sound-absorbing layer, and a foam layer (1.3) connected to it, the sound-absorbing layer (1.1) being formed of a porous absorber, preferably a fiber or foam fleece which has a permeability to air in the range of 150 to 2,000 liters / m at a pressure of 100 Pa²s. The sound-absorbing layer (1.2) is formed of a skin layer of the integral foam layer (1.3), at least 0.5 mm thick, and is joined with the porous absorbent with locking due to material, by subsequent foaming of the porous absorbent, essentially without perforating the foam. In addition, a process for producing such a coating is described.

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HW05831-8

Descriptive Report of the Invention Patent for LIGHT COVERING, SOUND INSULATION, FOR A PART OF THE BODY OF A MOTOR VEHICLE AND PROCESS FOR ITS PRODUCTION.

The present invention relates to a light, sound-insulating coating for a body part of a motor vehicle, especially in the form of a light front wall covering, comprising a layer of sound absorber, a sound-absorbing layer essentially air-tight, directly joined with the sound-absorbing layer, and a foam layer connected to it. In addition, the invention relates to a process for producing such a coating.

Conventional front wall coverings for motor vehicles are made up of a heavy sound-absorbing layer and a foam or textile fleece layer, the foam or fleece layer acting as an elastic spring and the heavy layer as a mass of a acoustic spring-mass system. As a heavy layer, then mats or molded parts of thermoplastic elastomer (TPE) or EPDM are used, which often contain filler material, for example barium sulfate or calcium carbonate. The heavy layer has a relatively high weight. It often has a specific weight of 2 to 4 kg / m², including even a specific weight between 4 and 8 kg / m². Like the elastic spring, a soft PUR foam or a fleece layer of polyester or cotton fibers is usually employed. The specific weight of these front wall coverings is therefore, as a rule, above 3.5 kg / m², which is unfavorable with regard to a reduction in the total vehicle weight or fuel consumption. Especially when, to improve the sound absorption capacity, the side of the heavy layer opposite the foam layer is coated with a sound absorbing surface of, for example, PET fleece, due to a relatively high number of the various materials used, a manufacturing for these front wall coverings correspondingly expensive in time and cost.

From DE 27 35 153 A1 there is known a specifically light spring-mass system, executed as a double mat, consisting of soft open-pored polyurethane foam and a heavy polyurethane foam covering layer filled and specially executed as a wall covering of a motor vehicle. The black polyurethane foam is then made as integral foam, has a Shore A hardness of 80 to 90 and contains an additional loading fraction of 400 to 500% by weight. To obtain the mentioned degree of hardness, a mixture of the usual hard foam polyol and the commercially available soft foam polyol is employed. The cover layer and the soft polyurethane foam layer are joined together by subsequent foaming, and the cover layer is inserted into a mold and later foamed with the soft polyurethane foam. The production of this well-known double mat is also relatively expensive in time and cost.

The present invention aims to provide a sound-absorbing and sound-absorbing coating, especially a front wall covering for motor vehicles, which is light in weight and can be obtained at relatively low cost. In addition, a process for the low-cost production of such a sound-insulating coating must be indicated.

This objective is achieved, initially, by a coating with the characteristics of claim 1.

The coating according to the invention comprises a sound-absorbing layer, an essentially air-tight sound-absorbing layer, directly connected with the sound-absorbing layer, and a foam layer connected thereto. The sound-absorbing layer is made up of a porous absorbent, preferably of a fiber or foam fleece, which has a test pressure of 100 Pa with an air permeability in the range of 150 to 2,000 liters / m²s. The sound-absorbing layer is, according to the invention, formed of a layer of skin of the integrated foam layer, at least 0.5 mm thick, the sound-absorbing layer being joined with the last with locking due to to the material, by later defoaming the porous absorbent essentially without perforating the foam.

The sound-absorbing layer and the foam layer are thus produced from the same starting materials in an individual process step and are integrally joined together in the finished coating. Preferably, the foam layer is then a layer of soft polyurethane foam with a skin layer essentially free of pores, serving as a sound-absorbing layer. Avoiding a heavy layer produced from another material, for example ethylene-propylene-diene-cautchu (EPDM), as well as eliminating the process of bonding a sound-absorbing layer on the heavy layer or damping layer of sound, with the coating according to the invention considerable weight reduction as well as cost savings can be achieved.

The porous absorbent, which preferably consists of fiber fleece or open-pore foam, is attached with a lock due to the material - without bonding - with the sound-absorbing layer (skin layer). Thanks to a relatively high air permeability, the porous absorber has a high sound absorption capacity. The high air permeability of the porous absorbent, however, is unfavorable in terms of avoiding the perforation of the foam in relation to the posterior defoaming of the absorbent. The inventors, however, solved this problem by favorable procedural measures, so that the sound absorbing capacity of the porous absorbent is barely impaired by subsequent foaming.

According to an advantageous configuration of the coating according to the invention, it is envisaged that the sound-absorbing layer will present surface areas of different thickness locally, the difference in thickness being at least 1 mm, especially at least 2 mm. Thus, the acoustic insulation effect of the weight-reducing coating can be optimized by taking into account the uneven distribution of the sound level.

As for the process for producing the coating according to the invention, the above objective is achieved by the process with the characteristics of claim 16.

The process according to the invention is essentially characterized by the fact that an absorbent layer of porous sound, preferably formed of fiber fleece or open pore foam, which presents a permeability to air in the range at a test pressure of 100 Pa from 150 to 2,000 liters / m²s, it is directly foamed later with a reaction mixture containing polyol and isocyanate in a foaming tool, the reaction mixture being introduced into the foaming tool essentially parallel to the rear side of the sound absorbing layer and / or parallel to the bottom area of a foam tool cavity, and since a predetermined partial region of the foaming tool surface is so hardened and / or during the introduction the polyol to isocyanate mixture ratio is so altered that the reaction mixture results in a foam layer, which presents a integral skin layer, essentially air-tight, at least 0.5 mm thick, which is joined with the sound-absorbing layer with locking due to the essentially non-penetrating shape of the foam. The introduction or further flow of the reaction mixture parallel to the back side of the porous absorbent prevents a perforation of the foam or penetration of the porous absorbent.

The process according to the invention allows the use of standard fiber fleece, especially bulk fleece, polyethylene fibers, polypropylene fibers, a mixture of polyethylene and polypropylene fibers, cotton fibers or a mixture of polyethylene fibers and natural. The fiber fleece used in the coating according to the invention must not have a special surface treatment; nor should it be specially impregnated. In the fiber fleece of the coating according to the invention, therefore, it may be a standard article.

A preferred configuration of the process according to the invention is that a limited volume of the reaction mixture is inserted in the foaming tool in such a way that the reaction mixture does not initially touch the porous absorbent, after which the locking union occurs due to the material between the reaction mixture and the porous absorbent as to the reaction of the reaction mixture.

Expressed in another way, the reaction mixture is so introduced into the foaming tool that the porous absorbent upon reaction (expansion) of the reaction mixture floats on it. The porous absorbent can then be attached or secured to the underside of one half of the foaming tool.

Other preferred and advantageous configurations of the coating according to the invention and the process for its production are indicated in the subclaims. The invention will be explained in detail below based on a drawing representing several examples of execution. Schematically show:

figure 1 - a sectional view of the front section of a motor vehicle with a sound-insulating coating, arranged on the inside of the front wall separating the passenger compartment from the engine compartment;

figure 2 - a sectional view of a section of a coating according to the invention;

figure 3 - a sectional view of a section of another example of making a coating according to the invention;

figure 4 - a sectional view of an open foaming tool for producing a coating according to the invention at the end of an injection stage;

figure 5 - a sectional view of the foaming tool of figure 4 in the closed state;

figure 6 - a sectional view of another foaming tool for producing a coating according to the invention at the beginning of the injection phase;

figure 7 - a sectional view of the foaming tool of figure 6 after the injection phase is closed;

figure 8 - a sectional view of another foaming tool for producing a coating according to the invention at the beginning of an injection stage;

figure 9 - a sectional view of another foaming tool for producing a coating according to the invention at the beginning of an injection stage; and figure 10 - a sectional view of a section of another foaming tool for producing a coating according to the invention after the injection phase is closed.

The sound insulating coating according to the invention is preferably carried out as an interior front wall covering 1 for a motor vehicle 2. But it can also be carried out, basically, as a sound insulating covering for other parts of the body of a vehicle. motor vehicle, for example as an engine hood or sliding roof.

In the embodiment shown in Figure 1, the lining 1 is adapted to the contour on the inside of a front wall 3, which separates the passenger compartment 4 from the engine compartment 5.

The coating 1 is self-supporting and stands out for its relatively small weight. Your total specific weight matters, for example, at less than 2,500 g / m^2, preferably less than 2,000 g / m² It features a sound-absorbing layer 1.1, a sound-absorbing layer 1.2 that is essentially air-tight and a foam layer 1.3 adjacent to that. The sound-absorbing layer 1.1 is formed of a fiber fleece. The sound-absorbing layer 1.2, on the contrary, consists of a layer of integral skin, at least 0.5 mm thick, of a layer of soft PUR foam. The sound-absorbing layer (skin layer) 1.2 is attached with a lock due to the material with the fiber fleece 1.1. For this, the fiber fleece 1.1 is subsequently foamed with a reaction mixture containing polyol and isocyanate, namely, preferably in a single step (one-shot-process), that is, in a single stage operation.

The subsequent defoaming of the fiber fleece 1.1 is carried out in such a way that a perforation of the foam by the fiber fleece is prevented. The sound-absorbing properties of the 1.1 fiber fleece thus remain essentially unchanged. For this purpose, for example, the flow direction of injection E of the reaction mixture is aligned parallel to the bottom side of the fiber fleece 1.1 or to the surface of the bottom half of the foaming tool.

The 1.1 fiber fleece is made up of polyethylene fibers, polypropylene fibers, a mixture of polyethylene and polypropylene fibers, cotton fibers or a mixture of polyethylene and natural fibers. It may then be a special volume fleece. It has air permeability in the range of 150 to 2,000 liters / m²s (measured at a test pressure of 100 Pa). Its longitudinal flow resistance is in the range of 5 kNs / m⁴up to 40 kNs / m⁴, preferably in the range of 5 kNs / m⁴ up to 25 kNs / m⁴.

The 1.1 fiber fleece has not been subjected to any special mechanical and / or chemical surface treatment, such as impregnation. The 1.1 fiber fleece to be foamed later is cut for example as a two-dimensional stamped part of a continuous fiber fleece. Observed by the cross section, the fiber fleece has an essentially uniform thickness as well as an essentially uniform flow resistance. As a fiber fleece, a standardized low-cost article can thus be applied to the coating according to the invention.

The specific weight of the 1.1 fiber fleece is in the range of 100 g / m² up to 1,600 g / m², preferably in the range of 100 g / m² up to 1,200 g / m². The layer thickness of the 1.1 fiber fleece matters, for example, in 2 mm to 30 mm, especially 5 mm to 20 mm.

For the production of the sound-absorbing layer 1.2, the coating of the soft PUR foam is used when the reaction of its mixing components in the defoaming tool. The thickness and density of the buffer layer 1.2 are controlled or influenced by the recipe of the reaction mixture and / or the temperature of the tool. The thickness of the sound-absorbing layer 1.2 matters, for example, in 1 mm to 5 mm. Its gross density is, for example, in the range of 0.08 to 2.0 g / m², preferably in the range of 0.08 to 1.4 g / m². The crude density of foam layer 1.3 is, on the contrary, in the range of 0.02 to 0.1 g / m², for example in the range of 0.02 to 0.06 g / m².

The subsequent defoaming of the 1.1 fiber fleece can be carried out either in a closed or open foam tool. The production of a coating according to the invention will be explained with reference to figures 4 to 10.

In figure 4, a foaming tool 6 is shown schematically in several parts. Other elements of the installation, such as storage tanks, containers with stirring mechanism, dosing pumps, tubular ducts, mixing heads, etc. are not represented, for greater visibility. The main components (isocyanate and polyol) of the reaction mixture are transferred from storage tanks to intermediate containers, brought to the required temperature and added through dosing aggregates to a mixing head (not shown), which is connected to one or more openings leakage 7 from the lower half 6.1 of the foaming tool.

Loading material can be added to the reaction mixture or its main components. As filler material, for example, barium sulphate and / or chalk are suitable. Optionally, however, load material can also be dispensed with. The loading material (BaSO₄ and / or chalk) is eventually combined with CO₂. By adding CO₂ the gross density of the soft foam layer 1.3 can be reduced.

The foaming tool 6 has a lower half of tool 6.1 and an upper half of tool 6.2, which together, in the closed state of the tool, define a cavity 8 corresponding to the coating to be produced. The upper half of tool 6.2 is designed to be lifted and lowered relative to the lower half of tool 6.1.

On the underside of the tool half 6.2, a piece made of a fiber fleece 1.1 is loosely attached. The carved part is produced, for example, by stamping. For loose attachment of the 1.1 fiber fleece, the underside of the tool half can be provided

6.2, for example, needles, especially needles with counter hook elements, adhesive tapes, coupling elements or the like.

The reaction mixture is introduced into the tool cavity 8 by one or more adduction channels 9 executed in the lower tool half (mold half) 6.2. The respective adduction channel is so executed that the direction of injection flow E of the reaction mixture is aligned essentially parallel to the underside of the fiber fleece 1.1 or to the bottom area 8.1 of the tool cavity.

The injection of the reaction mixture in the tool cavity 8 is done in the open state of the foaming tool 6. Thus, the reaction mixture does not initially touch the fiber fleece 1.1. After a limited or predetermined volume of the reaction mixture has been introduced into the foaming tool 6, the foaming tool is closed. The direct connection with locking due to the material between the reaction mixture and the fiber fleece 1.1 occurs during the reaction of the reaction mixture, which expands in cavity 8. The fiber fleece 1.1 then floats practically on the rising PUR foam.

The foaming tool 6 is provided with a tempering device, which comprises separately controllable fluid channels, integrated in the tool halves 6.1, 6.2, through which predetermined surface regions of the foaming tool 6, limiting the cavity 8, can be specifically seasoned (cooled).

Quenching of the surface regions of the foaming tool 6 means, in the present context, a relative cooling of the surface regions in question with respect to the reaction mixture of warmer soft foam.

The bottom half of tool 6.1 has a group of fluid channels 10, which are connected to a common dispensing duct (not shown), adding a fluid, and to a common collecting duct (not shown), discharging the fluid. The temperature of the fluid added to that group by fluid channels is so regulated that the tool surface closest to these fluid channels 10 has a temperature in the range of 50 ° C to 90 ° C, for example about 15 ° C at about 70 ° C or a temperature is set within the mentioned temperature range.

The fluid channels 11 integrated in the upper half of tool 6.2 form a second group of fluid channels, which are connected to another common distributor conduit (not shown), adding fluid, and to another collector conduit (not shown) discharging this fluid, the temperature of the fluid being so regulated that the surface of the upper half of tool 6.2 closest to the fluid channels 11 has a temperature in the range of 15 ° C to 60 ° C, for example about 15 ° C to 35 ° or a temperature is set within the mentioned temperature range.

The temperature difference between the surfaces of the tool halves 6.1, 6.2 delimiting the cavity matters at least 15 ° C, preferably at the same 25 ° C.

The foam structure of the soft foam layer results essentially from the propellant gases arising from the chemical crosslinking of the reaction mixture. CO₂ eventually added helps the defoaming process. Due to the relative cooling of the surface of the upper tool half 6.2 in relation to the surface of the lower tool half 6.1, the foaming process in the reaction mixture in the strip adjacent to the cooler tool surface is prevented, so that a skin 1.2 is produced there. integral, essentially free of pores, with a thickness of at least 0.5 mm, preferably at least 0.8 mm, particularly especially preferably at least 1 mm. The skin acts as a sound-insulating cushion 1.2. It is preferably airtight or at least essentially airtight. The skin 1.2 joins with locking due to the material with the back side of the fiber fleece 1.1

The fiber fleece 1.1 presents, from its application to the foaming tool 6, a temperature that is considerably below the surface temperature of the upper tool half 6.2. According to an advantageous configuration of the invention, it is provided that the fiber fleece 1.1 is cooled to a temperature in the range of 10 ° C to 15 ° C and fixed in that cooled state to the upper tool half 6.2. On the warmer surface of the lower half of tool 6.2, on the contrary, due to the foaming operation, a sound absorber 1.3 with open pores is formed, which has an open pore surface or just a very thin 1.4 skin, this skin being 1.4 thin is, however, permeable to sound or transparent to sound. The 1.4 sound permeable skin has a thickness of less than 400 pm, preferably less than 250 pm. It is for example thinner than 150 pm and can also only be partially executed.

The lining 1 according to the invention has, if necessary, on the edge side, a flexible sealing lip 12, which can compensate for any existing manufacturing tolerances and thus guarantee a fair adaptation of the lining 1 to the contiguous components or body sections ( see figure 2).

For the essentially pore-free configuration of the sealing lip 12, the lower half of the mold 6.1 is provided, close to the cavity section corresponding to the sealing lip, fluid channels 13, which are equally connected to the fluid distributor duct (not shown) associated with the second group of fluid channels 10. The fluid flowing through fluid channels 10 and 13 thus has the same temperature.

In the lower half of the mold 6.1, tappets 14 are also integrated, by means of which the finished molded part, therefore the coating 1, after opening the foaming tool 6, can be ejected.

In many sound insulating coatings for body parts, openings must be made, which are used, for example, for the passage of cables, hose ducts and / or mechanical aggregates. As shown in figure 2, in an opening 15 for a cable or hose conduit, an elastically expandable nozzle 16 is made for the sealed passage of the cable or hose conduit (not shown) on the protected side of the sheath 1, therefore on the side shown 1.2 full skin, essentially free from pores.

In figure 3 a section of a front wall 3 of a motor vehicle is shown in side view with a set of pedals 17 engaging through an opening 3.1 of the front wall. On the inner side of the front wall 3 there is a lining 1 according to the invention, which has an opening 18 for the pedal assembly 17.

Figures 6 and 7 show schematically another foaming tool 6 'for producing a coating 1 according to the invention. Unlike the foaming tool 6 according to figure 4, in the lower half of the mold 6.1, movable injection elements 19 are inserted. The injection elements 19 have respectively a tubular part 20, which is housed in a perforation 21 of the lower tool half

6.1 axially displaceable. The tubular part 20 is provided at its end facing the cavity 8 of the foaming tool 6 'of a deflector 22, whereby the reaction mixture containing polyol and isocyanate is radially deflected with respect to the tubular part. The deflector element 11 ensures that the reaction mixture is injected essentially non-perpendicularly onto the fiber fleece 1.1. Due to the deflector element 22, the injection flow direction E of the reaction mixture is aligned, essentially essentially parallel to the fiber fleece surface 1.1 or to the bottom area 8.1 of the cavity 8. Deflector element 22 can, for example, be executed in the form of a disc-shaped plate.

In the process according to the invention, however, it is perfectly possible that the reaction mixture when injected into cavity 8 also comes into direct contact with the fiber fleece 1.1 and flows along the underside of the fiber fleece. The injection flow direction E and, therefore, the main flow direction or pressure force of the reaction mixture are, however, aligned essentially parallel to the underside of the 1.1 fiber fleece. This essentially results in a laminar flow of the reaction mixture parallel to the underside of the fiber fleece 1.1.

It is also included in the scope of the invention to provide the porous sound absorbing layer 1.1 (for example fiber fleece) only partially in one or more partial regions of the coating 1 according to the invention. This applies in particular in the case of an opening for passing a cable or hose duct through the sheath 1 according to the invention. In a region, where 1.1 fiber fleece is not provided, the reaction mixture may also eventually be injected (poured) into the cavity perpendicularly with respect to the upper half of tool 6.2. In the 1.1 fiber fleece region, however, it is injected not perpendicularly with respect to it, but essentially in parallel to its underside.

The ends of the perforations 21 opening into the cavity 8 are respectively widened with a roughing 23, in which the deflector element 22 penetrates after the injection phase is closed. The injection elements 19 also serve as tappets for ejecting the finished molded part from the tool cavity.

Alternatively, the reaction mixture can also be sprayed or injected into a well of a tempered molding tool (not shown) and a piece carved from a 1.1 fiber fleece is then seated on the upper side of the introduced reaction mixture. The upper side of the newly applied soft foam and / or the fiber fleece 1.1 is then preferably cooled with respect to the tempered shaping tool. The fiber fleece piece is then preferably fixed with a support with respect to the upward reaction mixture. The fiber fleece 1.1 thus floats when expanding (foaming) the reaction mixture on the layer of soft foam 1.2 and joins, when the foam hardens, with locking due to the material with integral skin 1.2, essentially air-tight, from soft foam layer 1.3.

Figures 8 to 10 show schematically other foaming tools in various parts for producing coatings according to the invention.

The sound-absorbing layer 1.1, formed of a porous absorber, preferably of a fiber fleece, especially volume fleece, or of open-cell, air-permeable foam, may be arranged totally or partially on one side of the sound-absorbing layer. sound 1.2 foam14 da.

A coating according to the invention with a sound-absorbing layer covering only a partial area of ​​the sound-absorbing layer 1.2 can be produced with a foam tool 6, as outlined by way of example in figure 8. The lower tool half 6.1 defines a mold wall (mold area) 30, in which at least one recess (pocket) 31 is made to accommodate a cut piece of the air-permeable, porous sound-absorbing layer 1.1. The hollow compartment defined by recess 3.1 is essentially filled completely with the absorbent piece 1.1 inserted there. At the edge of the recess 31 or in its passage to the mold wall 30 of the tool half 6.1, a circumferential frame 32 is seated. The frame 32 prevents the reaction mixture R injected to produce the foam layer in the cavity 8 of the foaming tool 6 from flowing under the sound absorbing layer 1.1. Frame 32 covers the edge of the sound-absorbing layer

1.1 and extends along the edge of the recess 31 outwards. The frame 32 is made flat and consists, for example, of steel. It is coated with a separating agent (non-stick agent).

At least one injection channel 9 (so-called injection point) of the foaming tool 6 is so arranged with respect to at least one recess 31 housing a sound-absorbing layer that the reaction mixture R is introduced into the foaming tool 6 essentially parallel to the rear side of the sound-absorbing layer 1.1. In figure 8 by arrow E it is indicated that the reaction mixture R introduced into the cavity through the injection channel 9 flows essentially parallel to the rear side of the absorbent piece 1.1 inserted in the recess 31. The foaming tool also has a ventilation hole 33 leading to the cavity, which is executed, for example, in the upper tool half 6.2.

With 10 and 11 different groups of fluid channels are designated. Fluid channels 10 carry a fluid whose temperature is in the range of 50 ° C to 90 ° C, while fluid channels 11 carry a fluid whose temperature is in the range of 15 ° C to 60 ° Ç. The temperatures of the fluids are so regulated that between the surfaces of the tool halves 6.1, 6.2 delimiting each other the cavity 8 a temperature difference of at least 15 ° C, preferably at least 20 ° C, is adjusted.

In figure 9 a foaming tool 6 'is outlined for producing a coating according to the invention, which must have at least one opening for the passage of a conduit and / or a mechanical component. For this, a piece cut out of a sound absorbing layer 1.1 is used, in which at least one opening 15 'is already cut out.

The mold wall 30 of the foaming tool delimiting the cavity 8 is provided with at least one protrusion 34 in the form of a socket or a truncated cone, which is associated with the opening 15 'of the sound absorbing layer 1.1. The projection 34 crosses the opening 15 'of the sound absorbing layer 1.1, when it is inserted in the cavity 8 of the foaming tool 6'. The protrusion 34 has a circumferential rear cut, so that it covers the edge of the opening 15 'on the posteriorly foamed rear side of the sound absorbing layer 1.1 and thus prevents the injected reaction mixture R from flowing through the opening 15' to the front side of the layer sound absorber 1.1.0 rear section is formed, for example, by an impact plate 34.1, which is attached to the outer front side of the projection 34.

With the exception of the protrusion 34 crossing the respective opening 15 ', the sound absorbing layer 1.1 preferably consisting of an air-permeable fleece covers essentially the mold wall 30 of the tool half 6.1, delimiting the cavity 8 throughout the area. At least one injection channel 9 (injection point 7) of the foaming tool 6 'flows in front of the impact plate 34.1 or the front side of the projection 34 in the cavity 8, so that the reaction mixture R injected into the closed cavity is essentially introduced parallel to the rear side of the sound-absorbing layer 1.1 on the foaming tool, as shown in figure 9 by the arrow E. The foaming tool 6 'is, in turn, provided with ventilation channels 33, which end up in the cavity 8 close to the outer edge of the inserted sound absorbing layer 1.1.

Another advantageous configuration of the coating according to the invention is that only its sound-absorbing layer forms a flexible sealing lip 12 '. The sound-absorbing layer 1.1 is stamped on the edge side, that is, permanently sealed. It then extends laterally to the edge of the foamed sound-absorbing layer 1.2. The sealing lip 12 'can then extend along the entire periphery or also only along one or more partial sections of the edge of the sound-absorbing layer 1.2.

The embossing on the edge side of the sound-absorbing layer

1.1 preferably consisting of a thermoplastic fleece is shown in figure 10. The upper tool half 6.2 and the lower tool half 6.1 of the foaming tool 6^IV form a clamping region 35 at the edge of the cavity. The sound-absorbing layer 1.1 seated on the lower tool half 6.1 is so dimensioned that its edge, after closing the foaming tool 6^IV, is clamped in the clamping region 35. Clamping on the edge side of the sound absorbing layer 1.1 prevents the reaction mixture injected into the closed cavity from flowing through the edge of the sound absorbing layer 1.1. The introduction of the reaction mixture for the posterior foaming of the sound absorbing layer 1.1 is made by means of one or more axially displaceable injection elements 19, which correspond to the injection elements 19 represented in figures 6 and 7. The thickness of the 1.1 thermoplastic sound-absorbing layer, permeable to air, is preferably in the range of 10 mm to 20 mm. The thickness of the flexible sealing lip 12 ', on the contrary, is about 2 to 3 mm. The foaming tool 6^IV features a heating device associated with the clamping region 35, with which the sealed edge of the thermoplastic sound absorbing layer 1.1 can be heated to a temperature above 100 ° C, for example to about 120 ° C. The heating device comprises, in the example shown, fluid channels 36, in which an appropriate liquid, for example an oil, circulates. Alternatively, the heating device may also have electrical heating elements. For the rest, the foaming tool 6^lvit is provided, in turn, with fluid channels 10, 11, the temperatures of the fluids flowing there being regulated as mentioned above with reference to figure 8.

According to another preferred configuration of the coating according to the invention, it is envisaged that the porous absorbent 1.1 or a covering fleece additionally applied to it is formed of a flame retardant fiber fleece, preferably of polyester fleece. The coating is then preferably so equipped that it has a resistance to tempering at least 150 ° C. The coating according to the invention can be used, advantageously, in the region of a motor vehicle close to the engine or in regions similarly requested by temperature.

The execution of the invention is not restricted to the examples of execution described above. On the contrary, several variants are conceivable, which also make use of the inventive idea reproduced in the claims with basically divergent configuration. Thus, instead of the fiber fleece, a porous foam with open pores can also be used as a sound-absorbing layer. In addition, the coating 1 according to the invention can also, for example, have several partial sound-damping regions, that is, several integral skin regions, spaced apart, essentially free of pores, impermeable to air, which are specifically arranged on the covering 1 in accordance with the acoustic requirements for sound damping.