Sound-absorbing sandwich panel

Abstract

Sound-absorbing sandwich panel (10), comprising - a first layer (20) for sound absorption and / or sound insulation and - a second layer (30) for sound dampening and / or thermal insulation, which is firmly connected to the first layer (20) at its first main surface (32) and is intended for connection with an acoustically improved component (8) at its second main surface (38), characterized in that the second layer (30) is a bitumen-plastic foam layer with hollow bodies, in particular thermoplastic plastic hollow bodies or silicate hollow spheres, and with a density of 0.25 to 0.42 kg / dm³ 3 and preferably of 0.3 kg / dm² 3 is, and wherein the sandwich panel (10) has a surface weight of at most 2.5 kg / m² 2 exhibits.

Description

[0001] The invention relates to a sound-absorbing sandwich panel according to the preamble of claim 1.

[0002] Such a sandwich panel, which can also be referred to as a sound-insulating sandwich panel, is disclosed in EP 0 933 194 A2. This type of sound-absorbing sandwich panel, comprising a sound-absorbing layer and a vibration-damping layer, can be used in various ways to improve the acoustic properties of components. Examples include damping the vibrations of a floor panel, side walls, or the roof area of ​​a motor vehicle, and damping the vibrations of the walls of a household appliance. Typically, such a sandwich panel, with its vibration-damping layer, is bonded to the component to be acoustically improved, such as a floor panel or a washing-up tub.

[0003] In the case of motor vehicles or household appliances, for example, the problem arises that the surfaces of the flat housing parts, which are mostly made of sheet metal, are excited to considerable natural vibrations, making vibration damping indispensable.

[0004] In the automotive sector, there is an increasing demand for effective thermal insulation of specific areas combined with sound insulation or vibration damping to eliminate unwanted vibrations. Particularly in electrically powered vehicles, there is often a requirement that the corresponding vibration damping, sound-absorbing, or sound-insulating layers be as lightweight as possible without compromising their properties.

[0005] EP 09 33 194 A2 discloses a sandwich panel for sound damping, sound insulation and thermal insulation of a dishwasher tub, consisting of a layer of foam to be glued to the wall of the tub by means of an adhesive layer and a bituminous damping layer over 1 mm thick glued to this layer.

[0006] DE 36 31 075 A1 relates to a material for anti-vibration coatings containing bitumen or a bitumen-plastic mixture as well as porous fillers. To achieve a weight reduction, it is proposed to use clay materials containing hollow bodies as fillers, which are coated with a special material.

[0007] DE 196 24 314 C1 relates to a foam element for sound insulation of cavities, in particular of extruded profiles made of metal or plastic, which is compressed and sealed in an airtight film before being inserted into a cavity in such a way that it can be inserted into the cavity through an opening in the cavity, wherein the foam element expands after being inserted into the cavity by opening the film and supplying air into a shape that acts on at least two walls of the cavity.

[0008] DE 29 04 689 A1 relates to a covering membrane for structure-borne sound damping with low specific weight, consisting of at least one binder and at least one filler, characterized in that the filler is porous.

[0009] DE 30 45 924 A1 relates to a composition and methods for the production of foam compositions and the uses of these compositions. A foam composition comprises, for example, silicon dioxide hollow spheres in a polyvinyl alcohol-containing organic polyacid foam matrix.

[0010] DE 31 23 134 A1 relates to a composite material consisting of two metallic cover plates and an intermediate material located between the plates.

[0011] Furthermore, a damping coating for reducing the vibration of sheet metal is known from DE 101 63 035 A1, which provides a plastic-bitumen layer.

[0012] DE 10 2005 007 624 A1 discloses a coating for sound dampening with a stiffening layer formed from a thermoplastic.

[0013] The invention is based on the essential objective of further developing the aforementioned sound-absorbing sandwich panel in such a way that its damping effect can be improved with the lowest possible weight, as well as specifying methods for attaching such sandwich panels to a component to be acoustically improved.

[0014] This problem is solved according to the invention with a sound-absorbing sandwich panel according to claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

[0015] According to the invention, the sound-absorbing sandwich panel comprises a first layer serving for sound absorption and / or sound insulation, and a second layer serving for vibration damping and thermal insulation. The second layer is rigidly bonded to the first layer with one surface, which is referred to as the first main surface. The other surface (referred to as the second main surface) of the second layer, on the other hand, is intended to be bonded to the component that is to be acoustically improved, i.e., dampened or insulated with regard to sound propagation. The present invention is characterized in that the second layer is a bitumen-plastic foam layer with a density of 0.25 to 0.42 kg / dm³. 3 and in particular of 0.3 kg / dm³ 3 is.

[0016] The sound-dampening layer can also have additional thermal insulating properties and is then referred to as a thermal insulation layer. The sound-dampening effect is naturally achieved through the overall structure of the sandwich panel, with the present invention essentially aiming at an improvement of the second layer and its connection to the first layer and the component by means of suitable adhesive bonds.

[0017] According to an advantageous embodiment of the invention, the second layer has a modulus of elasticity in the range of 2000 to 4000 N / mm². 2 , preferably in the range of 2500 to 3500 N / mm 2 and in particular about 3000 N / mm 2This improves the transmission of vibrations or kinetic energy from the component to outer layers. For optimization, it can be advantageous if the first layer has a modulus of elasticity that is at least 10 times, preferably at least 20 times, greater than that of the second layer.

[0018] It is preferred that the first layer comprises at least one layer of aluminum or a thermoplastic (such as resin or PS) or thermoreactive (such as epoxy resin) stiffening layer of 0.05 to 0.5 mm, preferably 0.05 to 0.15 mm thickness, particularly preferably 0.10 to 0.15 mm, or a bitumen film or plastic film of 0.05 to 0.5 mm thickness.

[0019] According to the invention, the sandwich panel is designed to have a basis weight of no more than 2.5 kg / m². 2 , preferably no more than 2 kg / m² 2 and in particular about 1.5 kg / m² 2, exhibits.

[0020] A particularly good compromise between the space requirements of the sandwich panel and good sound-dampening and thermal insulation properties can be achieved if the sandwich panel has a thickness of no more than 5 mm, preferably no more than 4 mm, and especially about 3.4 mm. Advantageously, the second layer has a thickness in the range of 2 to 5 mm, preferably in the range of 2.5 to 3.5 mm, and especially about 3 mm.

[0021] In the sandwich panel according to the invention, the second layer preferably has hollow spheres, in particular hollow spheres filled with air, which significantly improves the sound dampening effect, but also improves the thermal insulation properties and keeps the weight low.

[0022] The following percentage values ​​for material compositions are given as weight percent, unless otherwise stated.

[0023] It can be advantageous to design the sandwich panel in such a way that the second layer contains approximately 50% bitumen, approximately 35% silicate hollow spheres, approximately 5.0% cellulose fiber, approximately 5.0% calcium oxide and approximately 5.0% ethylene vinyl acetate (EVA).

[0024] Furthermore, it can be advantageous if the second layer of the sandwich panel consists of an acoustic foil made of approximately 50% bitumen, approximately 10% sepiolite, approximately 5% silicate hollow spheres, approximately 30% ethylene vinyl acetate (EVA) and approximately 5% calcium oxide, and / or a lightweight bitumen foil made of approximately 40% bitumen, approximately 20% calcium carbonate, approximately 2.0% sepiolite, approximately 20% mica, approximately 10% silicate hollow spheres, approximately 5% ethylene vinyl acetate (EVA) and approximately 3% calcium oxide.

[0025] Alternatively or additionally, a thermoplastic rigid foam such as polystyrene or polyethylene can be used for the second layer.

[0026] Furthermore, the sound-dampening effect and thermal insulation properties can be improved by adding lightweight fillers to the second layer, thereby reducing its specific gravity. Suitable fillers include, for example, thermoplastic hollow bodies that expand thermally or thermosetting hollow bodies, as well as silicate hollow spheres, ground, open- or closed-cell, thermoplastic or cross-linked PE or PU rigid or flexible foams.

[0027] It can be advantageous if the second layer additionally contains thermoplastics, preferably EVA, PE, PP, and / or hydrocarbon resins.

[0028] It can also be advantageous to have a first adhesive layer bonding the first and second layers, and a second adhesive layer applied to the second main surface of the second layer for bonding to the component being improved. This allows kinetic energy to be converted into heat through friction within the two adhesive layers.

[0029] It can also be advantageous if the first layer is a thermoplastic or thermoreactive, in particular fiber-reinforced stiffening layer, especially made of epoxy, phenolic or formaldehyde resin or polystyrene.

[0030] By appropriately selecting the aforementioned parameters and materials, the sound absorption or insulation properties, i.e., the damping effect, can be optimized and individually adapted to the respective technical requirements, for example, the given space conditions or the natural frequency of the component to be damped.

[0031] For the aforementioned sandwich panels according to the invention, it should be noted that they have the same acoustic performance (i.e., sound dampening capacity) but weigh only about 50% of a conventional sandwich panel. With different dimensions, it is also possible for a sandwich panel 10 according to the invention to achieve even higher acoustic performance at a lower weight.

[0032] The problem underlying the invention is also solved with a sound-dampening layer and a sound-absorbing and / or sound-insulating layer, which are part of a sandwich panel according to the invention.

[0033] Further advantages, features and special characteristics of the invention will become apparent from the following detailed description of various embodiments of sandwich panels according to the invention. The following are shown: Fig. 1 in cross-section an advantageous embodiment of a sandwich panel according to the invention, Fig. 2 a diagram of the acoustic loss factor of the embodiment of Fig. 1 and Fig. Figure 3 shows a cross-sectional representation of the aforementioned embodiment to illustrate an advantage of the sandwich panel according to the invention.

[0034] Fig. Figure 1 shows a cross-sectional view of an advantageous embodiment of a sound-absorbing or sound-insulating sandwich panel 10 according to the invention, which for the sake of simplicity will be referred to below simply as a sandwich panel. The sandwich panel 10 is intended for application to a component 8, which is shown here only schematically. The sandwich panel 10 comprises a first layer 20, shown here above, which serves for sound absorption and / or sound insulation. A second layer 30 is attached to the first layer 20 directly or by means of an intermediate first adhesive layer 50, which may, for example, be a pressure-sensitive adhesive. Alternatively, a hot-melt adhesive may also be used, for example. The attachment of the second layer 30 to the first layer 20 is effected via the first main surface 32 of the second layer 30, i.e., via the surface shown here above.On the second main surface 38 of the second layer 30 (shown below), the second layer 30 is provided with a further, second adhesive layer 52, which can also be, for example, a pressure-sensitive adhesive or a hot-melt adhesive. With the help of this second adhesive layer 52, or directly, the second layer 30 is bonded to a component 8, which is to be acoustically improved or where sound damping is to be achieved.

[0035] According to the invention, this sandwich panel 10 is characterized in that the second layer 30 is a bitumen-plastic foam layer with a density of 0.3 kg / m³. 3 This reduces the specific weight and thus the overall weight of the sandwich panel 10. It has been shown that such a density results in particularly good sound-dampening properties for the sandwich panel as a whole (cf. Fig. 2).

[0036] The second layer 30 is advantageously 3 mm thick - with the thickness being measured in the direction from component 8 to the first layer 20 - and has a modulus of elasticity of approximately 3000 N / mm². 2 The first layer 20 is advantageously formed from 0.15 mm thick aluminum and has a modulus of elasticity of 71,000 N / mm². 2 Alternatively, a suitable plastic could be used for the first layer 20. Together with the two adhesive layers 50, 52, this results in a sandwich panel 10 with a total thickness of 3.4 mm and a basis weight of 1.5 kg / m². 2 .

[0037] The bitumen-plastic foam layer 30 can, for example, contain approximately 50% bitumen, approximately 35% silicate hollow spheres, approximately 5.0% cellulose fiber, approximately 5.0% calcium oxide and approximately 5.0% ethylene vinyl acetate (EVA).

[0038] The second layer 30 is advantageously expanded with lightweight fillers, which reduces the specific gravity of the second layer. Thermally expanding thermoplastic or thermosetting polymers can be used as expanding agents, but expanded hollow polymer bodies, silicate hollow spheres, ground, open- or closed-cell, thermoplastic or cross-linked PE or PU rigid or flexible foams are also advantageous.

[0039] It can be advantageous if the second layer contains 30 thermoplastics, such as EVA, PE, PP, and / or hydrocarbon resins.

[0040] The acoustic loss factor d of such a sandwich panel 10 is in Fig. Figure 2 shows the values ​​as a function of temperature for various frequencies, which are listed in the table to the right of the d-values. The standardized ISO method for characterizing the material properties of anti-vibration coatings is the Oberst method. This method involves exciting a strip-shaped specimen with a rectangular cross-section to bending vibrations. The specimen is suspended vertically and clamped at one end. The lower, free end is inductively excited by a vibration exciter. From the resonance behavior of the specimen, parameters describing the damping properties, such as the loss factor d, are derived. In this way, values ​​for the resonance frequencies are obtained; for all other frequencies, values ​​are obtained through linear interpolation or extrapolation.

[0041] As can be seen from the diagram and the table of Fig. As can be seen in Figure 2, the loss factor d for 500 Hz at a temperature of 0°C increases from 0.230 to 0.33 at a temperature of 20°C, after which it drops to 0.060 at a temperature of 80°C at 140 Hz. Such a sandwich panel 10 can advantageously be used in vehicle construction manually, by means of handling devices – i.e., semi-automatically – or by means of a robot application.

[0042] In Fig.Figure 3 shows an advantage of the present sandwich panel 10 according to the invention. The thick upper arrow S1 represents, by way of example, a large shear force acting on the sandwich panel 10 from above, while the thinner lower arrow S2 represents a smaller shear force acting on the sandwich panel 10 from below. The component 8, which is assumed to vibrate and is therefore to be dampened, transmits vibrational energy to the second (lower) adhesive layer 52. In the adhesive layer 52, some of the kinetic or vibrational energy is converted into heat by friction. Another part of the vibrational energy is absorbed by the second layer 30, since it is relatively shear-resistant and has a relatively high modulus of elasticity of 3000 N / mm². 2The vibrational energy is transferred to the first adhesive layer 50, where it is also converted into heat through friction. This improves the sound damping and insulation properties. It is evident from the above description that the second layer 30, formed from bitumen-plastic foam, serves as a shear-resistant spacer.

[0043] The loss factor of the second layer 30 is 0.02. Both the loss factor and the modulus of elasticity were measured using a 3 mm thick bitumen-plastic foam layer on 1 mm steel according to the Oberst method.

[0044] The described sandwich panels can, of course, also be used to advantage in a variety of other applications. An overview of preferred areas of application for various sandwich panels according to the invention is provided in Table 1.

[0045] For attaching a sandwich panel according to the invention to different surfaces of a component, there are, among others, the following advantageous procedures: 1. Application on flat surfaces: A sound-absorbing sandwich panel 10, comprising a first layer 20 made of aluminum, steel, or fiber-reinforced plastic (FRP) with a preferred thickness of approximately 0.05–0.5 mm and a second layer 30, is attached to the flat surface of the component 8 by means of an adhesive or hot-melt adhesive layer 52. The layers 20 and 30 are bonded to each other with an adhesive layer 50 or laminated on top of each other without adhesive. 2. Application to surfaces with contours (ribs): A sound-absorbing sandwich panel 10 has a first layer 20 made of a thermoplastic or thermoreactive material (resin, PS) and a preferred thickness of approximately 0.05–1 mm. The first layer serves primarily as a stiffening layer. The second layer 30 is provided with a hot-melt adhesive layer 52 on the second main surface 38. According to a first embodiment of this preferred design, the second layer 30 is first heated so that it conforms to the contours of the contoured surface of the component 8 under the melting conditions. During this conformation process, the second layer 30, which is particularly thermoreactive and made of, for example, epoxy, phenolic, formaldehyde resin, or PU, reacts. Subsequently, the first layer 20 can also be applied under heat.In another variant, both layers are heated simultaneously and thus adapt to the surface contour of component 8 and react through the heat treatment.

[0046] According to a further preferred embodiment of the present invention, the sound-absorbing sandwich panel 10 has a first layer 20 made of bitumen or plastic film with a preferred thickness of approximately 1.5 to 3 mm. These layers have preferred damping properties and, when applied to the second layer 30, can positively influence the damping behavior. The second layer 30 is applied to the component by means of a hot-melt adhesive layer 52, and the entire assembly is heated so that the first and second layers can conform to the contours of the component 8 and melt. Simultaneously, thermoreactive or thermoplastic layers can also be used here, which react accordingly when heated.

[0047] Preferably, the heating takes place at about 80 to 190°C, particularly preferably at about 100 to 140°C.

[0048] All of the above-described examples of the sandwich panel 10 according to the invention have in common that they exhibit very good sound absorption or sound insulation properties while simultaneously having very good thermal insulation properties.

[0049] Other examples of bitumen-plastic foam include: 1. Bitumen approx. 85%, expanding hollow bodies approx. 5%, thermoplastics approx. 10%, 2. Bitumen approx. 85%, ground foams approx. 5%, thermoplastics approx. 10%.

[0050] It should be noted that the features of the invention described with reference to individual examples of the invention, such as the design and arrangement of the individual layers and their density and thickness, the basis weights and the materials used, may also be present individually or cumulatively in other examples, unless otherwise stated or is prohibited for technical reasons. Reference symbol list 8 components 10 sandwich panels 20 first shift 30 second shift 32 first main page 38 second main page 50 first adhesive layer 52 second adhesive layer S1 second shear force S2 first shear force

Claims

[1] Sound-absorbing sandwich panel (10), comprising - a first layer (20) for sound absorption and / or sound insulation and - a second layer (30) for sound dampening and / or thermal insulation, which is firmly connected to the first layer (20) at its first main side (32) and is intended to be connected to an acoustically improved component (8) at its second main side (38), characterized by , that the second layer (30) is a bitumen-plastic foam layer with hollow bodies, in particular thermoplastic plastic hollow bodies or silicate hollow spheres, and with a density of 0.25 to 0.42 kg / dm³ 3 and preferably of 0.3 kg / dm² 3 is, and wherein the sandwich panel (10) has a surface weight of at most 2.5 kg / m² 2 exhibits. [2] Sandwich panel (10) according to claim 1, characterized by , that the second layer (30) has a modulus of elasticity in the range of 2000 to 4000 N / mm 2, preferably in the range of 2500 to 3500 N / mm 2 and in particular 3000 N / mm 2 exhibits. [3] Sandwich panel (10) according to claim 1 or 2, characterized by that the first layer (20) has a modulus of elasticity that is at least 10 times, preferably at least 20 times, greater than the modulus of elasticity of the second layer (30). [4] Sandwich panel (10) according to any one of the preceding claims, characterized by , that the first layer (20) comprises at least one layer of aluminium or a thermoplastic or thermoreactive, in particular fiber-reinforced stiffening layer of 0.05 to 0.5 mm, preferably 0.05 to 0.15 mm thickness, or a bitumen film or plastic film of 0.05 to 0.5 mm thickness. [5] Sandwich panel (10) according to any one of the preceding claims, characterized by that they have a surface weight of no more than 2 kg / m² 2 and in particular of 1.5 kg / m² 2 exhibits. [6] Sandwich panel (10) according to any one of the preceding claims, characterized by that it has a thickness of at most 5 mm, preferably at most 4 mm and in particular 3.4 mm. [7] Sandwich panel (10) according to any one of claims 1 to 5, characterized by , that the second layer (30) has a thickness in the range of 2 to 5 mm, preferably in the range of 2.5 to 3.5 mm and particularly 3 mm. [8] Sandwich panel (10) according to any one of the preceding claims, characterized by , that the second layer (30) comprises hollow spheres, in particular hollow spheres filled with air. [9] Sandwich panel (10) according to any one of the preceding claims, characterized by , that the second layer (30) comprises 50% bitumen, 35% silicate hollow spheres, 5.0% cellulose fiber, 5.0% calcium oxide and 5.0% ethylene vinyl acetate. [10] Sandwich panel (10) according to one of the preceding claims, characterized by, that the second layer (30) comprises an acoustic foil made of 50% bitumen, 10% sepiolite, 5% silicate hollow spheres, 30% ethylene vinyl acetate and 5% calcium oxide or a bitumen lightweight foil made of 40% bitumen, 20% calcium carbonate, 2.0% sepiolite, 20% mica, 10% silicate hollow spheres, 5% ethylene vinyl acetate and 3% calcium oxide. [11] Sandwich panel (10) according to any of the preceding claims, characterized by , that the second layer (30) contains blowing agents, preferably thermally expanding thermoplastic polymer bodies, and / or fillers to reduce the specific weight and specific heat capacity of the second layer (30). [12] Sandwich panel (10) according to any of the preceding claims, characterized by , that the second layer (30) contains thermoplastics, preferably EVA, PE, PP, and / or hydrocarbon resins. [13] Sandwich panel (10) according to any of the preceding claims, characterized by, that it has a first adhesive layer (50) connecting the first layer (20) and the second layer (30) and a second adhesive layer (52) attached to the second main side (38) of the second layer (30) for bonding with the component (8) to be improved. [14] Sandwich panel (10) according to any one of the preceding claims, characterized by , that the first layer (20) is a thermoplastic or thermoreactive, in particular fiber-reinforced stiffening layer, in particular made of epoxy, phenolic or formaldehyde resin, polyurethane or polystyrene. [15] Sandwich panel (10) according to claim 14, wherein a thermoplastic or thermoreactive layer is provided which reacts when heated at a temperature between 100 °C and 140 °C.

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