GB2179594A - A sandwich-like soundproofing element and method of manufacture - Google Patents

Abstract

The invention comprises a self-supporting sandwich-like soundproofing element which comprises two outer layers which are different and arranged with mutual spacing, and a core layer situated between them and consisting of plastics material foam. The core layer has a density increasing in the direction of the two outer layers and consists of a plastics material having preponderantly open cells.

Description

SPECIFICATION A sandwich-like soundproofing element and method of manufacture The invention relates to a self-supporting sandwichlike soundproofing element comprising two different covering or outer layers arranged with mutual spacing, and a core layer situated between the same and consisting of expanded plastics material, and to a method for the production of a soundproofing elementofthis nature.

Varied sound proofing elements are already known for application in the building industryfor the attenuation of sound conducted through the atmosphere, of sound conducted through solids and of sound generated by impacts orfootfalls, as well asthe attenuation of other noise such as from engines, compressors and the like. A known sound attenuator lining - according to DE-OS 33 34273 - incorporates and absorptive layer of openpored plastics material, on which a covering layer is applied on opposite sides. Asold layercomprising perforations is situated within the absorptive layer.The material ofthe absorptive layer is more rigid between the one covering or outer layer and the solid layer, i.e. this has a lower modulus of elasticity than the less rigid layer between this solid layer and the other outer layer which thus has a higher modulus of elasticity. A sound attenuator lining of this kind is provided to prevent air-conducted and solid-conducted sound emissions from metal sheet or plate elements.

Tothisend,thesoundattenuatorliningor facing is laid direct on the sound-emitting surfaces, one outer layer associated with the absorptive layer being formed by this metal plate. Sound attenuator linings of this nature are appiicable only to a limited extent, since onlythe emission ofsound from sheet or plate metal elements may be reduced thereby.

A soundproofing element is known - according to DE-OS 28 18252 - which comprises a pliable intermediate layer situated between two outer layers.

The two outer layers display a different hardness and the softer outer layer is situated - in the case in which the soundproofing element is installed to attentuate the onward conduction ofthe effect of sound - on surfaces of thins surface which conduct sound onwards, that is to say on the side of the soundproofing element facing away from the sound. Inserts may be incorporated at points orthroughoutthe area in at least one outer layer, for complementary reinforcement ofthe soundproofing elements. The sound emitted onto surfaces onwardly conducting sound may well be reduced thereby, but the application of these sou nd proofing elements could not comply with the conditions required in all cases of application.

A wire grid or grating joined to an expanded material element and supporting the same in at least marginal areas, is provided in the case of another known sound absorption element-accord- ing to AT-PS 373948. The grating simultaneously serves the purpose of secu ring the sound adsorption element, in which the extremities ofthe grating projecting beyond the expanded material elements are suspended in sections of a suspension structure. Resonance phenomena of the carrying elements securing the sound absorption element may well have been averted thereby in advantageous manner, but the sound attenuation values accomplished were not adequate for all spheres of application.

Astructural component is also known for sound insulation of space - as per AT-PS 373949 - in which an expanded material layer is joined to a hard plate of mineral fibre. The mineral fibre plate may moreover be covered with a layer of Kraft paper on its side facing towardsthe layer of expanded material. The mechanical strength of the structural component may well have been increased by the utilisation of a hard mineral fibre plate, but an adaptation ofthe structural componentto different conditions of application was not always possible to the required extent in this case either.

The present invention now has as its fundamental problem to devise a self-supporting sandwich-like sound proofing element which may be adapted to different conditions of application in uncomplicated manner. Furthermore, the application ofthesoundproofing element should be possible in motorvehicles in particular, for attenua- tion ofthe onward conduction of sound between the engines and the structural components outwardly radiating the sound, or between the structural components radiating the sound and the internalvolumeofthevehicle.Thesoundproofing element should be producible in an uncomplicated manner.

This problem ofthe invention is resolved in that the core layer has a density increasing in the direction towards the two outer layers and consists of a plastics material comprising pre ponderantlyopen cells.Asatisfactory attachment of the outer layers and a favourable oscillatory behaviour of the multilayerself-supporting sandwich-like soundproofing element is accomplished thanks to the compaction of the cellular structure in the two marginal portions ofthe core layer.The different oscillatory characteristic of the denser marginal portions as compared to the less dense central portion of the core layer leads to a composite oscillatory system which in each case attenuates sound at different frequencies and a satisfactory overall action is accomplished, in particular open attenuating sound emitted by engines orcompressors. Furthermore, this plastics material also referred to as expanded plastics material and having preponderantly open cells offers satisfactory protection against injuries in case of impact of persons and is also appropriate therefore for application in linings of internal volumes of passenger vehicles or cabs for commercial vehicles.An adequate strength for normal operation is secured however in view of the greater density in the area of the two outer layers in an unexpected manner thanks to the inventive solution, the advantage ofthe inventive solution also consisting inthatthe thickness as well as density ofthe compacted marginal portions of the core layer which are directly continguous to the outer layers may be adapted to different conditions in uncomplicated manner.

Provision Is made according to another feature of the invention to form the compacted cell structure in the two marginal portions facing towards the two outer layers from a mechanically andiorthermally compacted open-celled expanded plastics material . The advantage ofthissol- ution consists in that a unitary material ofsubstantial- ly identical expansive properties is formed, which remains permeable by air, to secure improved sound attenuation.Furthermore, it is advan tageousthatthis compaction may be performed dur- ing a processing operation distinct from the production of the expanded plastics material and that the remanentdeformation oftheopencelled cell structure by the action of pressure and/or temperature may be controlled precisely as a function ofthe desirable application conditions.

Another advantage ofthese operations occurring under pressure and/or heat consists in that it is possible in numerous cases to perform a spatial deformation of the soundproofing element inclusive ofthe two outer layers, atthesametime,to produce desirable spatial forms,forexample such as reoulredforinternal lining in motorvehicles.

Provision is made according to another advantageous modified embodiment, thatthevolumet- ricweightofthe open-celled plastics material foam of the core layer is different in the central portion and the marginal portions, the marginal portions however preferably having a volumetric weight which is two to five times as great as the central portion. It is simultaneously prevented thereby in an advantageous manner that a fracture of the outer layers or of the soundproofing element may occur under the action of a force, above all via a pointed object.

It is also possible howeverforthe central portion to beformedfrom asoftexpanded material, in particular having a volumetric weight of approximately 9to 10 kgs/m3, since a powerfully damping action is also accomplished thanks to the elastic flexibility of the core layer when persons collide with surfaces faced in this manner, apart fro the satisfactory sound attenuation behaviour ofthe elastic material, Provision is made according to another advan tageous development that the core layer be formed by a preponderantly open-celled soft expanded material, in particular an "MDI" expanded or reticulated polyether or polyester expanded plastics material. Foams of this nature are characterised by high elasticity and breaking strength and proved satisfactory forthe novel sphere of application.

rnvision is made according to anotherfeature of the Invention for the core layerto have a compacted cell structure in the marginal portionsfacing towards the two outer layers, which comprises a higher proportion of closed cells than the cell structure in a central portion between these marginal portions.Thankstothehigherpropor- tion of closed celis an d the com pacted cell structure, a greater resistance is opposed to traversal by air-conducted sound, thereby reducing the speed of propagation and facilitating its attenuation in the adjacent less dense but softer portions of the core layer.

It is advantageous furthermore if the soft expanded material is formed by an expanded plastics material, being an "MDI" expanded or reticulated polyether or polyester in particular, and the core layer is preferably formed buy a part of a block of soft expanded material, since it is possible thereby to secure a precise open-celled structure of low volumetricweight and a constant high continuity of the cell structure is accomplished through the thickness ofthe core layer.

It is also possible moreoverforthe core layer consisting of central and marginal portions to be made in one piece, whereby the numberofseparate partsforthe production ofthe inventive soundproofing elements may advantageously be reduced.

It is also possible however for the outer layerto be arranged to be damp repellent, in particular as a polyethylene foil, and forthe open cells ofthe marginal portion of the core layer to be in communcation with the ambient air via openings in the outer layer or the adhesive layer or the polyethylenefoil, thereby inhibiting the capillary action of the core layer comprising open cells, whereas humiditywhich had penetrated into this core layer may emerge from this core layer as water vapour.

On the other hand, it is also possible forthe damprepellent outer layer or polyethylene foil to be preceded atthe side facing away from the core layer by a fibrous mat comprising fibres orthreads impervious to high temperatures, which comprises really distributed openings and is constructed in reticu lar manner, thanks to which the soundproofing elements may also be installed close to sound generators radiating higher temperatures and an improved protection is present moreover against mechanical damage to the soundproofing elements.Thanks to the increased rigidity of the marginal portion associated with this fibrous mat, a large proportion of the incident sound is already absorbed during traversal ofthis part, and it is assured that thanks to the accessibility or rather air-permeability of this fibrous mat, the air may enter the soundproofing element without hindrance forthe purpose of sound attenuation.

In this connection, it is advantageous if the fibres or threads are formed by glass fibres and/or carbon fibres and/or metal fibres, since such mats of fibresorthreadsallowofhigh mechanical as well as thermal stressing and also withstand the adverse action of oils and greases.

Provision is made according to another modified embodiment that the surface of the other outer layer facing away from the fibrous mat has arranged on ita mat or water-repellentfibrousfieece and/or of expanded material, e.g. an open-celled soft foam, of which the thickness amounts to a small fraction of the thickness ofthe core layer, wherebythesound waves which had passed through the open-celled structure ofthe sound travelling towards the surface which is to be protected are also attenuated complementarily before impinging on this surface.

It is advantageous ofthe individual portions ofthe core layer are joined to each other and/orthe outer layer is joined to the core layer and/or the outer layer isjoined to the mat preceding the same and/orto the fibrous mat, via an adhesive layer, in particular to the cell framework of the core layer and the adhesive layer is made air-permeable, the adhesive layer preferably forming the outer layer, since the absorptivity ofthe core layer is not inhibited thereby by the adhesive layers present between the individual layers ofthe sandwich-like sound proofing element, in which connection the access to the open cells in the core layer is facilitated complementarily in the case of a connection of the layers to the cell structure only.

It is also advantageous ifthe adhesive layer is formed by the polyethylene foil formed as a cast foil, the operation for connecting the individual layers is thereby simplified thanks to the absence of the coat of adhesive.

It is also possible that an elastically deformable bearer unit which is air-permeable and/or sound-permeable in the direction ofthe outer layers is situated in the core layer and/or in the area between the core layer and the fibrous mat orthe mat.

Sound-proofing elements constructed in this manner may be adapted in uncomplicated mannerto complex spatial shapes, for example such as the internal shape of engine hoods or the like, and besecured on such parts via the bearer unit.

Provision is made according to another modified embodimentthatan elastically and in particular remanently deformable bearer unit is associ ated with the core iayer and is joined to the same in force-locked and/or shape-locked manner.

The deformation properties of the soundproofing elements produced in this manner may thereby be adapted to the different conditions of application and commensuratelytearout-prooffas- tening points may be provided.

It is also possible for the core layer to comprisetwo parts between which the elasticity deformable bearer unit is situated and bonded in. The core layer may be formed by two plates which in each case consist of a section of a block of soft expanded material with the bearer unit between them.

According to another modified embodiment the bearer unit and/or the adhesive layer and/or the outer layerand/orthefibrous matand/orthe mat are constructed to be permeable by water vapour. Impairments ofthe efficiency of the soundproofing element caused by humidity are thereby prevented.

According to the invention it is also possible that the fibrous mat is arranged to face a source of sound and the mat situated on the opposite top side is arranged to face a zone which is to be protected, the soundproofing element being situated between the sound source and a housing containing the same, e.g. an engine hood, and connected to the housing via the bearer unit, wherebyasound-insulatedfastening ofthesound- proofing elements on the surfaces which are to be protected, for example such as sheet metal parts of an engine hood orthe like is possible with facility.

It is advantageous if a thickness ofthe central portion differs in size compared to the thickness of the two marginal portions of the core layer, preferably being three times as great as that ofthe marginal portions, since an adaptation to the attenuation ofdifferentfrequencies of sound waves is thereby possible.

On the other hand, it is possible that the volumetric weight of the plastics material foam of the core layer differs between the central portion and the marginal portions, the marginal portion preferably having twice as great a volumetric weight asthecentral portion, wherebythe damping characteristics ofthe soundproofing element may complementarily be adapted with respect two thefrequencieswhich are to be attenuated, anda protection forthe very soft central portion against mechanical damage is simultaneously secured in uncomplicated manner.

Provision is made according to another form of embodimentthatthenumberofopencells differs between the central portion and the marginal portions of the core layer, and in particular increases from the marginal portions in the direction towards the central portion, thereby engendering labyrinth-like paths in which the sound energy is dimished.

It is also possible that an outer layer facing towards the one marginal portion ofthe core layer is formed by a fabric-like orfoil-like deformable material and the outer layer facing towards the other marginal portion is formed by a fibrousfleece and/or a cardboard impregnated with unsaturated polyester resin, and is preferably organised to be deformable and/or hardenable under heatand/ or pressure.Asandwich element is produced bythe utilisation of two flexible and deformable areal outer layers, which by virtue of the composite action ofthethree materials has a greater strength than each separate material by itself. Furthermore, it may be accomplished by the appropriate construction ofthe outer layers that a remanent contouring ofthe soundproofing element occurs during the deforming operation and the establishment of the sound attenuation characteristics may thus be combined with the shaping action into a single operation.

According to another modified embodiment it is also possiblethatan adhesive layer preferably formed by a polyethylene foil produced as a castfoil is situated between the outer layers and the core layer, and that the core layer and/or the adhesive layer and/orthe bearer unit and/or one or both outer layers are constructed to be permeable by air and to be humidity-repellent. It is accomplished thereby that by virtue of permeability by air, a satisfactory sound absorption effect of the soundproofing element and a protracted durability are secured simultaneously, since the liquid is barred by virtue ofthe liquid-repellentstructure of the outer and/or adhesive layers.

In another advantageous embodiment of the invention at least one of the outer layers andlor at least one ofthetwo marginal portions is provided with a supplemental humidity-repellant im pregnation. Because the corresponding outer layers or marginal portions are provided with a humidity-repellent impregnation, which is activated for example by the lneä.ing action during the deforming of the elements, an unacceptable absorption of humicitgo-Ft-he soundproofingg elements and thus a reduction ofthe soundproofing action may be prevented in uncomplicated manner.

Furthermore, it is also possible thatthe core layer comprises aereally distributed areal portions compacted in different degree, the weight of the core layer applicable to the same areal unit and the particular thickness in the areal portions compacted in different degree, being approximately the same.This modified embodiment has the great advantage that plate-shapad material of identical gauge may be utilised as an initial material forthe production of inventive soundproofing elements. In this connection, a differential compac ton occurs in surprisingly advantageous manger during the production of the inventive soundproofing elements in the areal portions which are compacted to a thinner or thicker gauge.

Thinner areal portions are thus compacted more intensively and thus acquire a greatervolumet- ric weight and a greater strength than thicker areal portions of these plates. An automaticadapta- tion of the strength properties to the different thicernesses, as commonly required in the case of facing elementsforthe internal lining of vehicles, is thus obtained indirectly.

The invention also encompasses a method forthe production of such soundproofing elements in which a core layer consisting of plastics material is joined in liorce-ioctwed manner to different outer 13yers.

This method is characterised in that a block offoam is expanded from soft expansible material and separated nto plates, whereupon heat is sup pliec to the surfaces cured away from each otherofone or two immediatelyadjacent plates, and at the same time these plates being acted upon bva compressive force acting in the direction of thecsn.ral layerandthe marginal portions ofthe pates being deformed plastically. Thanks to the heat and pressuretreatrnent ofthe plates of expanded material, it is possible to obtain different densities and cell structures within a one-piece element.

Pra-fision is made according to another modification ofthe method that an adhesive layer or an adhesive foil and if applicable a bearer unit, and a wire grid or the like is incorporated between the mutually confronting surfaces of two plates by means ofthe the supply of heat. Thanlcstothesimult- aneous application ofthe outer layers during this heat treatment, it is possible to save an additi onal bonding operation forthe fastening thereof on the surfaces of the marginal portions of the core layer.

It is also advantageous if outer layers are simultaneously applied on the opposite surfaces ofthe core layer and joined to the same in force-locked manner by the action of heat, one outer layer being formed by a fibrous mat and the other outer layer by a mat.

It is also possible forthe core layer and the bearer unit to be spatially deformed during the action of heat and force, since the expenditure for the pro duction of the core layers is reduced thereby and a more uniform cellular structure mayfurth ermore be assured throughout the thickness ofthe plate than in the case of individual production ofthe plates.

It is also advantageous if prior to the heating and compacting ofthe marginal portions ofthe plate, heat-sealable plastics material foils are applied on the surfaces and joined to the marginal portions ofthe core layer by the action of heat and force, since thefusing-on and fastening ofthe humidity sealing plastics material foils are simultaneously secured by the action of heat during the compacting ofthe marginal portions.

Itisalsopossiblethattheintensityand period ofthe action of force as well as the intensity and period of the action of heat are variable as a function ofthe desirable damping behaviourofthe plate, and identical in both marginal portions. The proportion of the closed cells in the marginal portions as well as the density and volumetric weight may be matched to the desirable attenuation characterised bycontrollingthecriteriaforthe method, such as the intensity and period ofthe action offorce or of the action of heat.

It is also advantageous ifthefibrous matallocated to the one outer layer and the mat allocated to the other outer layer are applied simultaneously and are joined in force-locked mannertothe surfaces ofthe outerlayerswhichfaceawayfrom each other, because dishing of the plates as well as the build-up of internal stresses are prevented thereby.

Another modification ofthe method is characterised in that at least a part of the core layer of uniform thickness, and preferably conjointly with at least one outer layer is placed in a mould underinterpositioning of an adhesive layer, in particular, a cast polyethylene foil, and is compacted to different densities in differentareal portions under simultaneous action of pressure and heat whilst the individual layers are simultaneously joined together and/or cured, after which the soundproofing element is preferably trimmed to the required peripheral shape during the same operation. This procedure renders it possible to producethe most varied soundproofing elements in uncomplicated manner under application of but little expense.In this connection, the advan tages of satisfactory sound attenuation and favourable behaviour in case of an accident are retained however thanks to the satisfactory damping qualities of such elements in case of collision with persons.

The invention will now be described by way of example with reference to the accompanying partly diagrammatic drawings, in which: Figure lisa diagrammatic, fragmentary partially exploded perspective view of a soundproofing element constructed according to the invention, Figure2 is a cross-section through a marginal portion of a core layer of an inventive soundproofing element, in which are apparent the points of connection to a diagrmmatically indicated foil acting as an outer layer and areas of adhesive application on the cell structure, Figure 3 is an end view ofan engine compartment with inventivesoundproofing elements installed at the inner side of the engine compartment and showing the arrangements for securing the soundproofing elements to the engine hood, Figure4is a diagrammatic fragmentary perspective view of a further soundproofing element according to the invention, FigureS is a cross-sectional elevation of another soundproofing element, Figure 6 is a fragmentary partly cut-away perspective view of a part of the core layer of an inven tive soundproofing element with diagrammatic illus- tration ofthe different cell structures in a compacted edge and in a central portion.

Aself-supporting sandwich-iike soundproofing element 1 is illustrated in Figure 1. This soundproofing element 1 incorporates two outer layers 2,3 and a core layer 4.

In the present embodiment, the core layer4 comprises two plates 5,6 of a soft expanded material which, as indicated diagrammatically, has ales- serdensityin a central portion 7 of the core layer4than in the marginal portions7 ofthecore layer4than in the marginal portions 8,9 ofthe core layer 4. A bearer unit 10, e.g. being a wire grid or mesh or a wire netting element, is situated between the mutually confronting surfaces of the two plates Sand 6 in the central portion 7 ofthe core layer 4. The bearer unit 10 is preferably elastic and may be deformed remanently into optional spatial shapes by the action of pressure.

An adhesive layer 11 which mayforexample by formed by a cast foil,for example a polyethylene foil orthe like, is provided for connection of the two plates 5,6 and of the bearer unit 10.

In the marginal portions 8,9 a fibrous mat 14 and a mat 15, respectively, which form the outer layers 2,3 are connected to the plates 5,6 equally via adhesive layers 12,13.

The adhesive layers 12,13 may again be formed by cast foils, for example a polyethylene foil. In case of application of polyethylene foils as adhesive layers, these are preferably provided with areally distributed openings, so that a traversal by air is assured between the plates 5,6 between these plates 5,6 and the fibrous mat 14 and the mat 15, respectively. Thanks to the incorporation of openings 16, the air may pulsate in the cells ofthe plates, so that the air-conducted sound oscillations are attenuated by the labyrinth-like passages in the open cell structure ofthe core layer 4 or ofthe plates 5,6 forming the same.It is assured by these openings 16that any humiditywhich may have penetrated into the sound-proofing element 1 may emerge in the vapour state. However a penetration of water in liquid form may be prevented in optimum degree, under appropriate selection of the size and number of the openings 16 situated in an areal unit.

Retainers 17 cooperating with connecting means 18 are secured on the bearer unit 10 for attachment of the soundproofing element 1 and fastening it on a component 19 which is to be protected againstthe effects of sound from a sound source 20.

The connecting means 18 mayfor example be formed by studs or screw orthe like secured on the component 19.

Fibres or thread 21 ofthefibrous mat 14may consist of glass fibres, metal fibres or carbon fibres orthe like, which areimperviousto high ted perature, primarily in the area of sound sources radiating highertemperatures, such as engines and compressors, depending on the purpose of application ofthe soundproofing element. Thanks to an embodimentofthis kind ofthefibrous mat, the adhesive layer 12 as well as the marginal portion 8 are protected against the action of excessive temperatures.

The mat 15 associated with the component 19 which is situated on the side ofthe soundproofing element facing away from the sound source 20 - is formed for example by a fibrous fleece or by a mat of soft expanded material. The outer layer 2, the fibrous mat 14, and the outer layer 3 and the mat 15, respectively, have respective thicknesses 22 and 23, which amounts to a small fraction of a thickness 24 ofthe core layer 4. The mat may be formed by a water-repellentfibrousfleece or by an expanded material mat of a soft expanded material comprising preponderantly open cells.

As shown by the diagrammatical illustration of the central portion 7 and ofthe marginal port ions 8,the core layer4 has a density increasing in the direction towards the two outer layers 2,3.

Whereas the central layer preferably has a volumetric weight of 10 kg/cm3, the volumetric weight of the soft expanded material amounts to approximately 18 to 20 kg/m3 in the marginal portions 8,9. Different sound transversal valuesarethereby obtained acrossthethickness ofthe core layer 4, so that sound attenuation values of approximately identically satisfactory nature are obtained for different frequencies with a soundproofing element 1. Furthermore, a greater strength and stability of the core layer4 are secured in the marginal portions 8 and 9 thanks to the greater density in the marginal portions 8,9. Advantageous conditions are secured thereby forthefasten- ing ofthe outer layers 2,3 on the core layer. Thanks two the greater strength of the marginal portions 8,9 the soundproofing element may be constructed to be self-supporting only by connection to the outer layers, in the absence of additional measures. It proved to be advantageous if the different volumetric weight of the marginal portions 8,9 compared to the central portion 7 of the core layer4 is established by the fact that plates of identical density are compacted in the marginal portions by the action of pressure and temperature. Whilst doing so, the collapse ofthe open-celled cell structure caused bythe action of heat in these compacted portions results in a greater number of closed cells than in the central portion 7.An adaptation of the soundproofing element to different soundsourcesordifferentfrequenciesofsound waves emitted bysuch sound sources may be regulated by an appropriate variation ofthe thickness of the marginal portions 8,9, and ofthe density as compared to the density of the central portion 7. Plates which are cut out of a block of soft expanded material are preferentially utilised for the core layer,forthis purpose. The soft expanded materials utilised forthe production ofthe plates may consist of a polyether or polyes ter plastics material I foam, in particular on which is "MD" expanded or reticulated.The advantage of utilising plates which are cut out of a block of expanded plastics material consists inthatthe density and the cell structure are of optimum uniformity.

In this connection, it is immaterial within the ambit ofthe invention whether the core layer 4 is formed by a single plate or by two plates 5 and 6 as illustrated in Figure 1, or by several plates of different density or cell structure, e.g. one plate for the central portion 7 and one plate each forthe marginal portions 8,9.

It is now possible to proceed in accordance with the following method to produce a soundproofing element 1 ofthis kind, such as illustrated in Figure 1: Plates between which a bearer unit 10, e.g. consisting of wire netting or mesh is positioned,are produced from a soft expanded material having a constant densitythroughoutthe thickness. Use may be made of plates 5,6 cut out of a block of expanded plastics material consisting of soft foam, between which are situated an adhesive layer 11 and the bearer unit 10. The outer layers 2 and 3 with adhesive layers 12 and 13 are together inserted into a heated press forthe production of soundproofing element 1.

Following this, the press is heated to a temperature of between 1 00two 1 150 C in the area ofthe outer layers 2,3 and an areal load of appropriate magnitude is applied on the soundproofing element 1 laid in the mould. The cell structure in the marginal portions 8,9 is caused to collapse by the areally distributed load undersimultaneous ac- tion of heat, leading to a reduction ofthethick- ness ofthe core layer4 because ofthis compacting operation.A higher density of the expanded material is engendered in the marginal portions 8,9 bythe collapse as a result ofthe simultaneous action of pressure and heat The thickness of the marginal portions or rather the change in density may be adapted in uncomplicated mannerto different cases of application byappropriateselec- tion ofthetemperature and pressure loading.

The adhesive utilised for the adhesive layer 11,12 and 13 is preferably water-repellent but permeable by air, so that the air may penetrate without hindrance into the portions situated behind the same ofthe plates 5,6 and core layer4.

It is possible to make use of cast foils, for example polyethylenefoilsforisolation of humidity and for bonding together of the separate layers ofthe sandwich-like soundproofing element 1, instead of the adhesive layers. Upon heating the soundproofing element 1, this foil meits and acts as a water-repellent protective layer and at the same time as an adhesive for the bonding ofthe separate layers of the soundproofing element 1.

Thanks to the utilisation of open-pored expanded materials having highly elastic properties in the area of the core layer 4 and in the area of the outer layer3, the inventivesoundproofing element1 may be installed directon thecomponent 19 which is to be protected againstthe incident sound.

To this end, it is advantageous ifthe connection between the connecting means and the retainer 17 on the bearer unit loins established via elastic intermediate elements, so that a transmission of vibrations and thus of sound to the component 19 is reliably prevented.

A part of the core layer 4 is illustrated in Figure 2. As apparent, this core layer comprises closed cells 25 and the interconnected open cells 26 which are formed by the reticular structure.

So that a passage of air may now be rendered possible through the layer of adhesive between the outer layer3 and thecore layer4, use is made of an adhesive 27 which has a consistency which does not allow of overbridging layer cavities, so that the adhesive 27 is applied onlyto the reticular structure ofthe open cells 26 orto the closed cells 25.

It is assured thereby that air passages through which the air may enter into and emerge from the core layer 4, are left in the area ofthe joint between the outer layer3 and the core layer 4.

The arrangement of inventive soundproofing elements 1 on the inner side of an engine hood 28 comprising hood members 29 and 30 formed by gI ass4ibre reinforced plastics material, is shown in Figure 3. Inside the engine hood 28 is situated a diesel engine 31 which emits sound conducted by air and through solids, as denoted symbolically by arrows 32 and 33, in all directions. The soundproofing elements 1 are connected to the hood members 29 and30via the bearer unit 10 and connecting means 18.

As also apparentfrom Figure 3, it is possible thanks to the deformability of the elements of the inventivesoundproofing element, to adaptthesame to optional spatial deformations ofthe hood members 29 and 30, as shown in the case ofthe soundproofing element 1 associated with the hood member 29.

According to the invention, it is possible to make use of "TTI" expanded plastics material foams instead ofthe "MDI" expanded plastics material foams.

The selection of the densities of the plastics material foam in the marginal and central portions, may be varied appropriately to secure an improved attenuation behaviourfor more powerful power oscillations.

It is also possible to make use of a cotton fibre fleece or of a fleece of synthetic fibres, for the mat 15. If an adhesive is utilised forthe adhesive layer, care should be exercised to ascertain that the same still retains its adhesive action even after a heating operation to approximately 150"C, or is liquidified in this temperature range, so thatthe bonding of the separate plates or layers may be undertaken simultaneously during the stressing of the soundproofing element by heat and pressure, to assure that a durable bonded joint is obtained within the sandwich. Known heat press mechanisms may be utilised during the production or deformation for the application of pressure and heatto the soundproofing element.

A soundproofing element 101 comprising an outer layer 102, an outer layer 103 and a core layer 104 arranged between them, is shown in Figure 4. As shown diagrammatically, the core layer 104 comprises a central portion 105 and two marginal portions 106,107. This core layer 104 may consist of a one-piece expanded plastics material preponderantlycomprising open cells, suitably being a plate of expanded plastics material. It is also possible however to join together marginal portions and a central portion consisting of separate plates. As indicated by the diagrammatical illustration in the cross-sectional surface in the area of the end side,the marginal portions 106,107 and the central portion 105 have a different density of the open-celled plastics material foam.

These marginal portions 106,107 are formed to this end frorn open-celled plastics material foam compacted under pressure, i.e. mechanically and/or thermally. The plastics material foam having identical properties is preferentially utilised in this embodiment for the central portion 105 as well as for the marginal portions 106,107. If use is made of a one-piece core layer 104, the marginal portions 106,107 are produced by compaction performed in the surface area under simultaneous supply of heat. As also shown by the illustration of Figure 4, areal portions 108 have a greater thickness 109 than the area portions 110, which mere lyhaveathickness 111 The core layer 104 is more greatly compacted in the areal portion 110 and commensurately has a higher density and thus a higher volumetric weight.This occurs because the open-celled structure is compacted more intensively by the increased pressure in the areal portions 110 under simultaneous thermal loading. In this connection, it is also possible to exposethe areal portions which are to be compacted more intensively to a highertemperature too, to facilitate the collapse or permanent deformation ofthe open-celled plastics material structure.

An element of identical surface preferably hasthe same weight in the areal portion 110 of lesser thickness 111 and in the area portion 108 of greater thickness 109. The outer layers 102 and 103 may be formed by foils deformable under pressure and heat or reticular materials offabric, fibres or other synthetic or natural materials. It is preferantiallythat one ofthe two outer layers 102,103 is produced from a cardboard impregnated with unsaturated polyester resin. In one embodiment, in which one outer layer 102 is formed by a board impregnated with unsaturated polyester resin, this outer layer 102 is faced to a vehicle body 112, for example to the sheet metal parts of the passenger compartment.The fastening between the soundproofing element 101. or rather the outer layer 102, and the body 112 may be established by means of appropriate plastics material or metal securing devices. The oppositely situated outer layer 103 may consist of mats formed from synthetic or natural fibres, or of leather orthe like. If the outer layers 102 and 103 areto bejoined together directly during the production of the inventive soundproofing elements 101, for example by application of cast foils 113 as shown diagrammatically in the lower section of Figure 4, care should be applied to assure that the outer layers 102 and 103 allow of a commensurate elastic deformation and heating loading.

In the case of the soundproofing element 101 illustrated,the soft expanded material of plastics material foam of open-celled structure which is utilised may for example have a density of approximately 9 to 10 kgs/m3, and is compacted to a density of app roxi mately 40 to 50 kgs/m3,for example in the areal portion 110 in which it has a thickness 111 only. This has the result that a greater stability of the sandwich element with respect to the areal portions 108 is established by virtue of the denser structure ofthesoft foam in the areal portion 110, andthatan adequate resistance to damage is assured in normal operation in those portions in which a thickness 109 ofthe soundproofing element 101 is impossible because of structural conditions.For all that, it is accomplished however in the case of a soundproofing element of this kind that a high degree of elasticity and satisfactory damping properties under collision with persons are obtained, since the stronger and more highly compacted areal portions 110 merge direct into areal portions 108 of higher elasticity and that on the whole the more highly compacted areal portion 110 is also damped more elastically than in the case of being with expanded plastics material comprising preponderantly closed cells.

The density gradient in the marginal portions 106 and 107 may also diminish progressively in the direction of the central portion 105, thanks to appropriate action offorceand heatduringthe production of the inventive soundproofing elements.

Across-section through a soundproofing element 1 14which mayforexample be utilised as a cladding element in a vehicleforthe purpose of internal volume lining, is shown in Figure 5. As apparentfrom this view the soundproofing element 114 comprises areal portions 115,116,117 and 1 l8ofdifferentthick- ness and of different deformation. A core layer 119 and an outer layer 120 associated therewith should allowfor an adequate deformation to enable con touring ofthe soundproofing element without destruction of material.To this end, it is possible that the very highly compacted and thinned areal portions 117,118 orat least individual areal portions and for the purpose ofsecuring an appropriate adequate strength for installing connecting means, and advantageously the core layer 119, to have arranged therein bearing units 121 which after the shaping of the core layer 119 hold and stabilise these areal portions 117,118 in the form specified. The bearer unit 121 may consist of net orfoil shaped elements im pregnatedwith different resins or other adhesives or of grids and netsformedfrom metalsorthelike, which harden after deformation and heat treatment and keep the soundproofing element 114 in this desirable form.

It is also possible in the case of this soundproofing element 1 14 that another outer layer may be applied on the side ofthe core layer 119 opposed to that of the outer layer 120.

A part of a core layer 122 and of an outer layer 120 is shown in greatly simplified form and graphic illustration in Figure 6. This illustration provides a graphic representation of the operation ofthe mechanical and thermal compaction of the marginal portions 123 as compared to a central portion 124.As apparent, the open cells 126 in a marginal portion 123 facing towards a surface 125 of the core layer 122, which are formed by a spatial lattice of plastics material comprising a plurality of webs 127 are squeezed together by the mechanical and thermal compaction, whereby the approximately spheroida! cells or spheroidaliy structured webs 127 are compressed and fractured and partially enclosed closed cells 128 for example assume an elliptical shape as compared to the central portion 124 in which they are approximatelysphero ida!. The open cells 126 or the webs 127 forming these are compressed and deformed by the pressure and heat, thereby increasing the strength as well as the density in the marginal portion 123.If this com action occurs areally, it diminishes linearly or grad- ually in the direction ofthe central portion 124 as a function oftheprocessing criteria selected, until the central portion 124, in which the original unaltered cell structure is retained.

The solution according to the invention consequently differs from the soundproofing elements in which an expanding action incorporating the for ming of a skin is exploited, so that a hard surface is obtained in the case of a soft core, by virtue of the fact thatthe compaction of marginal portions by means ofthe heat and pressure applied is controllable within optional iimits. It is merely the fundamental concept ofthe inventive solution consisting in varying the properties of soft expanded material plates by appropriate compaction which is illustrated diagrammatically in Figure 6.

The application ofthe inventive method and device is not restricted, in respect of the outer layers incorporated. For example, it is possible to utilise fabrics, natural or synthetic leather, fibrous fleeces, nets or knitted fabrics as outer layers, in which connection it is possible to apply both natural as well as synthetic fibres. These outer layers may preferably also be impregnatedwith humidity-repellent or stronglyfire- resistant substances or coated with these. In this con nection, it is advantageous ifthese additionally app- lied or incorporated materials do not harden into the required shape until the pressure and heattreatment following the deforming ofthe soundproofing el ements.A resilient action returning the soundproof ing elements to their initial setting is reliably preven ted thereby.

Analogously, any optional material is utilisablefor the bearer unit 121. It is thus possible to utilise app ropriate fibrous fleeces, fibrous netsorthe like, of metal, plastics material or natural fibres and threads, and preferably carbon fibres.

It is advantageous if this bearer unit is coated with an unsaturated polyester resin so that the bearer unit is held fast after the deforming operation in this def ormed position during the heat and/or pressure app lication.

It is also possible to place the bearer unit between two appropriate constructed plates of expanded mat erial and to join the same to these plastics material layers via one or two adhesive layers, for example cast foils.

The inventive soundproofing elements are pre ferentially utilisableforthe internal structure in motor vehicles, in particularforthe lining of passen ger compartments, or drivers' cabs in the case of commercial vehicles. They are also advantageously utilisable for insulation in high-rise buildings or in the case of sound attenuation in the area of mach ines.

Claims (38)

1. Aself-supporting sandwich-like soundproof ing element comprising two different covering layers arranged with mutual spacing and a core layer consisting of expanded plastics material situated there between characterised inthatthecorelayerconsists of expanded plastics material having preponderantly open cells and has a density increasing in the direction towardsthetwo covering layers.

2. A soundproofing element according to claim 1, characterised in that the cell structure of the core layer in the marginal portions facing towards the two covering layers is formed by compacted open-celled plastics material foam.

3. A soundproofing element according to claim 1 or claim 2, characterised in that the volumetric weight of the open-celled plastics material foam of the core layer is different in a central portion and marginal portions on opposite sides thereof and fac ing the covering layers, the marginal portions having a volumetric weight which is two to five times greater than that of the central portion.

4. A soundproofing element according to claim 2 or claim 3, characterised in that the central portion is formed from a soft expanded material, having a vol umetrioweight of approximately 9to 10 kgs/m3.

5. A soundproofing element according to any one of the preceding claims, characterised in that the core layer is formed by a preponderantly open-celled soft expanded material comprising an "MDI"- expanded or reticulated polyether or polyester plastics material foam.

6. A soundproofing element according to any of claims 2 to 5, characterised in that the core layer in corporates a compacted cell structure in the marginal portions facing towards the two outer layers, which has a greater proportion of closed cells than the cell structure in the central portion between these marginal portions.

7. A soundproofing element according to claim 1, characterised in that the core layer is formed by a part of a block of soft expanded material consisting of a polyether or polyester plastics material foam which is "MDI"-expanded or reticulated.

8. A soundproofing element according to claim 1, characterised in that the core layer comprises a central portion and marginal portions facing the cover- ing layer and is formed in one piece.

9. A soundproofing element according to any preceding claim, characterised in that a covering layer is formed to repel humidity and that the open cells of marginal portions of the core layer facing the covering layer are in communcation with the ambient atmosphere via openings in the covering layer.

10. Asoundproofing elementasclaimed in claim 9, in which the covering layer is a polyethylene foil.

11. Asoundproofing element as claimed in claim 9 or 10, characterised in that the humidity repellent outer layer is preceded on a side facing awayfrom the core layer by a vibrous mat comprising fibres or threads impervious to high temperatures and which comprises really distributed openings in net-like manner.

12. A soundproofing element according to claim 11, characterised in that the fibres orthreads are formed by glass fibres and/or carbon fibres and/or metal fibres.

13. Asoundproofing elementaccording to claim 11 or claim 12, characterised in that a mat layer of water-repellent fibrous fleece and/or expanded material having a thickness of a small fraction ofthe thickness ofthe core layer is present on the surface of the other outer layer facing away from the fibrous mat.

14. A soundproofing element according to any preceding claim characterised in that the individual portions of the sandwich-like structure are joined together via adhesive layers which are permeable by air, the adhesive layer preferably forming the outer layer.

15. Asoundproofing element as claimed in claim 14, in which an adhesive layerforms an outer layer of the sandwich-like structure.

16. A soundproofing element according to claim 14 or claim 15, characterised in that an adhesive layer is formed by a polyethylene foil produced as a cast foil.

17. A soundproofing element according to any preceding claim, characterised in that an elastically deformable bearer unit which is air- and soundpermeable in the direction of the outer layers is situated within the sandwich-like structure.

18. Asoundproofing element according to any preceding claim, characterised in that a deformable bearer unit is secured to the core layer.

19. A soundproofing element according to claim 18, characterised in that the core layer comprises two parts between which the deformable bearer unit is secured.

20. A soundproofing element according to any preceding claim characterised in that sandwich-like structure is constructed to be permeable by water vapour.

21. A soundproofing element according to claim 13, characterised in that the fibrous mat is arranged to face a sound source and the mat situated on the opposite side is arranged to face a zone or compo nentwhich is to be sound-protected, and soundproofing element being situated between the sound source and a housing containing the sound source and connected to the housing.

22. A soundproofing element according to claim 1, characterised in that the core comprises a central portion and marginal portions facing the covering layer, the thickness of the central portion being substantially three times as great as that of the marginal portions.

23. A soundproofing element according to one of the claims 1 to 20, characterised in that the volumet ricweight of the plastics material foam ofthe core layer differs between a central portion and marginal portions, the marginal portion having twice as great avolumetricweight as the central portion.

24. A soundproofing element according to claim 3 orclaim 23, characterised in thatthe numberof open cells per unit volume differs between the central portion and the marginal portions of the core layer, and increases from the marginal portions in the directiontowardsthecentral portion.

25. A soundproofing element according to any preceding claim, characterised in that an outer layer facing towards one marginal portion of the core layer is formed by a fabric-like orfoil-like deformable material and the outer layer facing towards the other marginal portion is formed by a layer deformable to a stable deformed condition.

26. A soundproofing element according to any preceding claim, characterised in that an adhesive layerpreferablyformed bya polyethylene foil produced as a cast foil is situated between the outer layers and the core layer, and that the sandwich like structure is constructed to be permeable by air and comprises at least one humidity-repellent layer.

27. A soundproofing element according to one of the claims 1 to 24, characterised in that at least one of the outer layers and at least one marginal portion of the core layer are provided with a supplemental impregnation for repelling humidity.

28. A soundproofing element according to any preceding claim, characterised in that the core layer comprises really distributed areal portions compacted in different degree, the weight of the core layer applicable to the same areal unit and the particular thickness in the areal portions compacted in different degree, is approximately the same.

29. A method for production of soundproofing elements according to any of claims 1 to 28, in which a core layer consisting of plastics material is joined in force-locked manner to different outer layers, characterised in that a block of foam is expanded from soft expansible material and separated into plates, whereupon heat is supplied to the opposite side surfaces of one or two immediately adjacent plates, and at the same time in particular, these plates being acted upon by a compressive force acting in the direction ofthe central layer, and the marginal portions ofthe plates being deformed plastically.

30. A method according to claim 29, characterised in that an adhesive layer or an adhesive foil and if applicable a bearer unit, comprising a wire grid orthe like, in incoporated between the mutually confronting surfaces of two plates by means ofthe supply of heat.

31. A method according to claim 29, characterised in that outer layers are simultaneously applied on the surfaces ofthe core layer facing away from each other bythe action of heat and thereby joined to the core layer in force-locked manner, one outer layer being formed by a fibrous mat and the otherouterlayerbya mat.

32. A method according to any one of the claims 29 to 31, characterised in that the core layer and a bearer unit secured thereto are spatially deformed during the action of heat and force.

33. A method according to any one of the claims 29 or 32, characterised in that priorto the heating and compacting ofthe marginal portions of the plate heat-sealable plastics material foils are applied on the surfaces and joined to the marginal portions of the core layer bythe action of heat and force.

34. A method according to any one of the claims 29 to 33, characterised in that the intensity and period of the action of force as well as the intensity and period ofthe action of heat are variable as afunction ofthe desired damping behaviourofthe plate, and identical at both marginal portions.

35. A method according to claim 31, char- acterised in thatthefibrous mat allocated to the one outer layer and the mat allocated to the other outer layer are applied simultaneously and are joined in force-locked manner to the surfaces ofthe outer layers which face away from each other.

36. Amethodforthe production of soundproofing elements are claimed in any of claims 1 to 26, characterised in that at least a part of the core layer of uniform thickness, and conjointly with at least one layer is placed in a mold under interpositioning of an adhesivelayer,formed as a castpolyethylenefoil, and is compacted to different densities in different areal portions under simultaneous action of pressure and heat whilst the individual layers are simu Itaneouslyjoined together and/or cured, after which the soundproofing element is preferablytrimmedto the required peripheral shape during the same operation.

37. A soundproofing element substantially as described with reference to the accompanying partly diagrammatic drawings.

38. A method of producing a soundproofing el ementsubstantial ly as described with reference to the accompanying drawings.