EP3336256A1 - Transparent sound absorbing acoustic baffling element - Google Patents

Abstract

Noise protection element for the insulation and absorption of sound emissions of vehicles, in particular road vehicles and rail vehicles and of aircraft moving along a traffic route, comprising a plate (1) of transparent material on which a sound absorbing material (3) is applied.

Description

The present invention relates to a noise protection element for the insulation and absorption of noise emissions from vehicles, in particular motorized vehicles, which move along a traffic route.

In the construction of noise barriers on public roads, transparent elements made of window glass, laminated safety glass, polycarbonate or acrylic glass are often installed. Such elements are commonly referred to as sound-insulating or sound-reflecting elements. In practice, these are usually solid sheets in thicknesses of 8-30 mm. Although these have high airborne sound insulation, they can not be used in all situations due to their sound-reflecting properties.

The currently available on the market transparent sound-absorbing elements are characterized in that the reverberant surface of the transparent element such. Glass, acrylic or polycarbonate a special noise-absorbing frame system or absorbent post / post system is used, which has noise-absorbing properties. Although such elements have a very good sound absorption in the reverberation room (test according to DIN EN 1793 Parts 1 and 2) but not in an application along a traffic route, where these transparent sound absorbing walls do not show a sufficient sound absorption effect.

Another embodiment of the noise absorbing elements is based on the cassette system, as is common for example in aluminum or wooden walls. It is a cassette with a transparent front, which has openings, and a compact back of transparent material without openings. The perforated front of such an element is ajar against marketable aluminum elements and has openings that can have different shapes and sizes. Are known round or elongated openings or circularly arranged slots in the transparent plate.

Other technical solutions are based on the principle of Helmholtz resonators and show a sound absorption only in certain frequencies. Such systems have been known for years, but there is a lack of either the acoustic properties of the elements or the actual effectiveness and long-term stability. In addition, such systems are not suitable to absorb the entire spectrum of traffic noise.

Another embodiment of a transparent sound-absorbing element is the so-called Clearwall system. This elaborately designed system consists of transparent panes, in front of which perforated aluminum swords with noise-absorbing properties are mounted perpendicular to the surface of the panel.

The above-described systems have in common that they are comparatively expensive in their construction and production and correspondingly expensive. In addition, it has been shown that such soundproofing elements can be further improved with regard to their sound insulation and, in particular, sound absorption properties when used along a traffic route.

It is thus the object of the present invention to provide an easily manufactured and at least partially transparent noise protection element which, with a relatively small space requirement and comparatively low weight when used along a traffic route, has outstanding sound absorption and at the same time a relatively low sound reflection.

A further object of the present invention is to provide a noise barrier which comprises an at least partially transparent noise protection element, has outstanding sound insulating properties and low sound reflection. It is important here that the noise protection wall, when used at the edge of a traffic route, essentially absorbs the entire spectrum of traffic noise.

These objects have been achieved according to the invention in a surprisingly simple manner by the noise protection element according to the invention and the noise protection wall according to the invention.

The noise protection element according to the invention is characterized in that the desired sound absorption, according to the new acoustic standards 1793-5 and 1793-6 (measurement of the in situ airborne sound insulation), takes place directly on the transparent solid plate. As a rule, the sound-absorbing material is distributed evenly over the board and thus shows very good sound absorption values over the entire spectrum of traffic noise.

The noise protection element according to the invention comprises a plate made of a transparent material, wherein a noise-absorbing material is applied to at least one of the two surfaces of the plate.

The transparent material may be inorganic glass or an organic polymer. In particular, silicate glass can be used as the inorganic glass. In particular, a suitable organic polymer may be a polymer comprising a polycarbonate, polyalkyl (meth) acrylate, e.g. Polymethyl methacrylate (PMMA), a polymethyl methacrylimide (PMMI) or mixtures thereof. In a preferred embodiment, the organic polymer consists essentially of polycarbonate, PMMA or PMMI.

In a particularly preferred embodiment, the transparent material is PMMA. Corresponding materials are commercially available from Evonik Performance Materials GmbH (Darmstadt, Germany) under the brand name Plexiglas®. Usually corresponding plates made of PMMA by extrusion or by the Kammergießverfahren from methyl methacrylate. In the latter, the liquid polymerizable monomer mixture is filled in a flat chamber formed of two parallel glass plates and a sealing cord circumscribing at the edge thereof. After closing the fill port, the filled chamber is exposed to the polymerization conditions until the monomer mixture has cured to PMMA.

Commercially available PLEXIGLAS® Soundstop panels are particularly well suited for use in the noise protection element according to the invention. These may optionally be reinforced by embedded polyamide or steel filaments or by a mesh of such filaments, thereby preventing the formation and fall-off of loose fragments of such a plate upon damage. Corresponding PMMA plates are for example in the patent DE 199 47 704 B4 described.

Composite materials can also be used as transparent materials as long as they have sufficiently high transparency.

Preferably, the transparent material has a light transmission D ₆₅ , measured according to ISO 13468-2, of at least 70%, preferably at least 80%, particularly preferably at least 90%.

In one embodiment, at least one of the two surfaces of the plate may be at least partially frosted or satin, i. so that the plate is translucent, but not transparent. This effect can be achieved by tarnishing or coloring the transparent material or by working the surface of the plate. The satinizing of a glass surface can be achieved, for example, by roughening with the aid of a sandblasting technique or treatment with hydrofluoric acid. Sheets of a polymeric material such as PMMA can be matted or calendered by mechanical, thermoplastic or chemical matting processes. Corresponding methods are known to the person skilled in the art. For example, mechanical matting techniques may include sandblasting, sanding with abrasive paper and abrasive cloths, or rotating brushes. As an example of thermoplastic matting, thermoforming can be mentioned. Dulling with chemical substances, such as solvents, is also possible. These dissolve the polymeric transparent material such as PMMA and thus structure the surface of the plate.

In the production of extruded sheets of a polymeric material such as PMMA, matte structures can be embossed into smooth extruded film webs by means of roughened embossing rolls in a roll calender. On the other hand, if the plate is made by the chamber casting method, the inside of at least one of the two glass plates may have a rough surface and thus create a matte structure on the corresponding surface of the plate. Both methods are sufficiently known to the person skilled in the art.

In a further embodiment, matting agents, for example particulate scattering agents, may be added to the transparent material. This procedure is particularly suitable for the production of extruded sheets of PMMA, which consist of a frosted layer. Alternatively, the plate may be a multilayer coextruded plate comprising a base layer containing no particulate scattering agent and at least one scattering layer with a particulate scattering agent.

The choice of noise absorbing material for the noise control element of the invention is not particularly limited as long as the material has suitable noise absorbing properties and is sufficiently weather resistant. For example, the sound absorbing material may be an organic or inorganic foam, or glass wool or rock wool. Preferably, however, a polymer foam is used as noise-absorbing material, which may be, for example, a polyolefin foam, polyurethane foam or a polyalkyl (meth) acrylimide foam.

A polyolefin foam may, for example, be a polystyrene foam, a polyethylene foam or a polypropylene foam, the polyethylene foam and the polypropylene foam being particularly suitable for the use according to the invention because of their excellent weathering stability.

In the present application, a polyethylene foam or a polypropylene foam is understood as meaning a foam whose polymer component comprises polyethylene or polypropylene. The polymer component can be pure polyethylene or polypropylene, a copolymer of ethylene or propylene or a mixture of polyethylene or polypropylene with at least one further polymer.

As examples of suitable polymer foams may be mentioned Ethafoam Whisper®, Stratocell Whisper® FR or Stratocell Whisper® DB which are commercially available from Sealed Air (NC, USA).

In the noise protection element according to the invention, both an open-pore and a closed-pore polymer foam can be used. However, the use of a closed-cell polymer foam is preferred because the uptake of water and dirt by such a polymer foam is significantly lower. The area-related water absorption of the polymer foam used by diffusion acc. EN 12088 (RH> 95%, 28 days) is usually not higher than 10 kg / m ² , more preferably not higher than 5 kg / m ² , particularly preferably not higher than 3 kg / m ² .

The nominal density of the polymer foam used, measured according to ISO 845: 2006, is typically between 5 and 100 kg / m ³ , more preferably between 10 and 70 kg / m ³ , especially preferably between 20 and 50 kg / m ³ and very particularly preferably between 20 and 40 kg / m ³ .

The polymer foam used according to the invention generally has good noise-absorbing properties. It is preferred that a 50 mm sample of the polymer foam, when measured according to EN ISO 11654 a sound absorption coefficient α _w of at least 0.6, preferably at least 0.7, more preferably at least 0.8, more preferably at least 0.9 and more preferably has at least 0.95. These values correspond to a sound absorber class C, more preferably a sound absorber class B and particularly preferably a sound absorber class A.

In one embodiment, the polymer foam used may have a substantially uniform density and pore size between 0.5 mm and 30 mm, more preferably between 1 mm and 20 mm, even more preferably between 1 mm and 15 mm. Particularly advantageous for absorbing the typical frequencies of traffic noise is a pore size distribution between 1 mm and 10 mm.

In an alternative embodiment, the polymer foam used has a pore size between 0.5 mm and 30 mm, wherein about 30% of pores have a size between 0.5 mm and 5 mm, another 30% have a size between 5 mm and 10 mm and another 40% Size between 10 mm and 30 mm. Such distribution allows a particularly efficient absorption of the entire traffic noise spectrum.

In a preferred embodiment, the noise absorbing material is applied to the plate in the form of several strips. The strips of sound-absorbing material may be arranged parallel to each other, e.g. be arranged substantially horizontally, obliquely or vertically, parallel to the traffic route. If a filament-reinforced PMMA sheet is used as the transparent material, the strips of noise-absorbing material may be applied such that the filaments are at least partially obscured by the parallel strips of sound-absorbing material and are not visible to the viewer.

At least one surface of the sheet of transparent material may have a plurality of recesses. The cross section of the recesses may be, for example, triangular, trapezoidal, funnel-shaped, oval or rectangular. These recesses can already be incorporated in the plate during the production of the plate, for example during the extrusion, or else subsequently in a prefabricated plate, for example by milling. Subsequently, elements of the sound absorbing material can be inserted into the prepared recesses. Furthermore, it is possible that the sound-absorbing material such as foam is already polymerized into this during the manufacture of the plate.

In the inventive use of the noise protection element, the recesses are aligned in the direction of the noise source (traffic route) and contribute significantly to the noise absorption. The recesses in the plate may be at least partially covered and / or filled by the sound absorbing material. In the latter case, the recesses serve not only as Helmholtz resonators but also as an anchorage for elements of the sound-absorbing material.

In a further embodiment, the plate of a transparent material has no recesses. The sound absorbing material, typically a polyolefin foam, may be applied directly to the surface of the board, for example by means of an adhesive or mounting tape. Because no recesses are necessary for this, the production costs for the corresponding noise protection element are significantly lower. Furthermore, it is possible to apply the sound-absorbing material to noise protection elements that have already been installed in noise barriers.

Furthermore, the noise absorbing material may form non-linear regular or irregular patterns in the form of trees, shrubs, branches or geometric figures such as circles, triangles, rectangles or hexagons.

Furthermore, it is possible to apply the sound absorbing material in the form of different width and spaced at different intervals strip on the surface of the plate, horizontally, obliquely or vertically to each other. By adjusting the distances between the strips, the noise absorption for certain frequencies can be further optimized.

In a particularly preferred embodiment, the recesses form a pattern of a plurality of parallel, for example horizontally extending, straight lines which extend over the entire surface of the plate. The there anchored strip-shaped elements of the sound-absorbing material are thus also aligned parallel to each other. In particular polyolefin foams are particularly suitable as noise-absorbing materials for this embodiment, wherein the use of polyethylene foams has proved to be particularly advantageous.

So that an optimal sound absorption can be achieved, the distribution of the sound-absorbing material on the surface of the plate takes place as evenly as possible.

The part of the polyolefin foam projecting beyond the surface of the plate may have different geometries and sizes. It can be rectangular, triangular, trapezoidal, semicircular, oval or any other shape with a textured surface shape, such as lamella or fir tree shape.

It has surprisingly been found that excellent noise absorption can already be achieved when about 10% to 50%, particularly preferably 20% to 30% of at least one surface of the plate is covered by the sound-absorbing material. The rest of the surface of the plate usually remains transparent to the viewer. Thus, the transparency of a noise protection wall, in which the noise protection elements according to the invention are used, retained to a large extent. Consequently, the noise protection element according to the invention combines the advantages of already known completely transparent noise protection elements (such as PLEXIGLAS® Soundstop) with those of significantly more complex noise-absorbing systems which are non-transparent.

As further advantageous, an embodiment has been found in which the sound-absorbing material in the form of several different widths and arranged at different distances strip is applied to the surface of the plate. This arrangement allows a particularly efficient sound absorption in a wide frequency spectrum.

The noise protection element according to the invention can be used in a noise protection wall for the insulation and absorption of noise emissions from vehicles, in particular motorized vehicles, which move along a traffic route. These include in particular road vehicles, rail vehicles, maglev trains and take-off and landing aircraft. The road vehicles include in particular vehicles with an internal combustion engine, electric drive or a hybrid drive. Rail vehicles may be, for example, trams, trains and high-speed trains. The " traffic route " for the purposes of the present invention may be a road, a highway, a railway line (railroad track) for passenger and freight traffic or a runway for civil and military aircraft.

Furthermore, the noise protection element according to the invention can be used in a noise protection wall for the insulation and absorption of sound emissions from departing and landing helicopters, in particular on helicopter landing pads.

The noise protection wall according to the invention generally comprises a plurality of noise protection elements according to the invention, which are aligned along the traffic route. In order for optimum sound absorption to be achieved, the sound-absorbing material is located on a surface of the plate facing the traffic route.

Because the noise protection element according to the invention for the viewer in a vehicle appears largely transparent, it allows a largely undisturbed view of the surrounding landscape while driving. At the same time, the noise protection element according to the invention effects an efficient sound absorption and only a small sound reflection, so that both the vehicle occupants and the surroundings of the traffic route are exposed to a significantly lower noise level.

Examples Example 1 - Test acc. ISO 354

12 identical 25 mm thick PMMA sheets (PLEXIGLAS® Soundstop GS CC commercially available from Evonik Performance Materials GmbH, length: 1000 mm, height: 1000 mm) were used. The properties of the PMMA sheets are summarized in Table 1 below: Table 1 Density acc. ISO 1183 1.19 g / cm ³ Weight 29.7 kg / m ² Tensile strength acc. ISO 527-2 / 1B / 5 70 MPa Elastic modulus acc. ISO 527-2 / 1B / 5 3,300 MPa Thermal expansion coefficient 0 ° to 50 ° C acc. DIN 53752-A 70 x 10 ⁶ K ^-1 Poisson 12:37

In the plates 1 a plurality of triangular recesses 2 were milled at a distance of 125 mm (see Fig. Figures 1 and 2 ). Foam strips 3 with a 40 x 40 mm cross-section were inserted into the prepared recesses. The foam used was the commercially available polyethylene foam Stratocell Whisper® UV. The characteristics of Stratocell Whisper® UV are listed below: Table 2 Density acc. ISO 845: 2006 (ASTM D3575-08 W) 25 kg / m ³ Water absorption (RH> 95%, after 28 days), acc. UNI EN 12088 <3 kg / m ² Thermal conductivity acc. ISO 845: 2006 (ASTM D3573-08 V) 0.104 W / (m · K) (23 ° C) 0.082 W / (m · K) (-5 ° C) Thermal stability acc. ISO 845: 2006 (ASTM D3573-08 S) <3 thickness 40 mm

Acoustic properties of the noise protection elements were tested in a test gem. ISO 354 examined. The ISO 354 standard describes a method for measuring the sound absorption coefficient of acoustic materials used as wall or ceiling cladding.

The measurement results are summarized in Table 3 and by the diagram in the FIG. 3 graphically represented: Table 3 Frequency, Hz 100 125 160 200 250 315 400 500 630 800 1 000 1 250 1 600 2000 2500 3150 4000 5000 RT (sec) 1225 1582 2767 4174 4929 5844 6221 6859 5882 5059 4.99 4789 4495 4105 3288 2.98 3049 2558 RT (sec) 1165 1573 2611 3298 4008 4079 4233 4129 3824 3284 3075 2718 2306 2078 1784 1728 1816 1627 A 1:40 12:14 0.72 2:08 1:53 2:42 2:47 3.15 2.99 3:49 4:08 5.19 6.89 7.74 8:35 7.90 7.20 7.20 α 12:12 12:01 12:06 12:17 12:13 12:20 12:21 12:26 12:25 12:29 12:34 12:43 12:57 0.65 0.70 0.66 0.60 0.60

The test results demonstrate a particularly advantageous sound absorption behavior at frequencies between 1 250 Hz to 5 000 Hz, where the absorption coefficient α of more than 0.40 is achieved.

Example 2

In a 25 mm PMMA sheet (PLEXIGLAS® Soundstop GS CC commercially available from Evonik Performance Materials GmbH, length: 1000 mm, height: 1000 mm), several rectangular recesses were milled out at a distance of 125 mm (see FIG. 5 ). In the prepared recesses rectangular foam strips were used with a 40 x 50 mm cross-section.

Subsequently, the acoustic properties of the noise protection element were determined according to the standard EN 1793. The measurement results are summarized in Table 4: Table 4 Absorption coefficient α 100 12:20 125 12:33 160 12:09 200 12:11 250 12:29 315 12:41 400 12:40 500 12:49 630 0.60 800 0.68 1 000 0.66 1 250 0.61 1 600 0.64 2,000 0.67 2 500 0.69 3,150 0.65 4,000 0.67 5,000 0.71 DLα 4dB Sound absorption class A2

This noise protection element also has very good noise absorption properties.

Comparison with commercially available noise protection elements

• Dieselbox (erhältlich von Dieselbox SA) und
• Alfa (erhältlich von Alpa Acoustiki Ltd.)

The sound absorption behavior of the tested noise protection elements from Example 1 (EVONIK (ISO 354)) and Example 2 (EVONIK (EN 1793)) was compared with the behavior of the two commercially available noise protection elements:

• Diesel box (available from Dieselbox SA) and
• Alfa (available from Alpa Acoustiki Ltd.)

Both commercially available noise protection elements have a comparatively complex structure and their acquisition is associated with correspondingly high costs. Furthermore, it should be noted that the noise protection system Alpha is non-transparent.

The results of the comparison are summarized in Table 5 and graphically in the FIG. 4 shown. Table 5 frequency EVONIK (EN 1793) EVONIK (ISO 354) DIESELBOX ALPHA 100 0.2 12:12 12:12 12:51 125 12:33 12:01 12:14 12:53 160 12:09 12:06 12:26 12:55 200 12:11 12:18 12:40 12:56 250 12:29 12:13 12:55 0.69 315 12:41 0.2 12:57 0.76 400 0.4 0.2 0.65 0.71 500 12:49 12:26 12:53 0.62 630 0.6 12:25 12:39 12:53 800 0.68 12:29 12:33 0.70 1 000 0.66 12:35 12:31 0.68 1 250 0.61 12:45 12:34 0.64 1 600 0.64 12:58 12:28 0.83 2,000 0.67 0.64 12:23 0.85 2 500 0.69 0.7 12:18 0.74 3,150 0.65 0.65 12:13 0.81 4,000 0.67 0.6 12:10 0.68 5,000 0.71 0.6 12:50

The comparison shows that the noise protection elements according to the invention have particularly good noise absorption properties in the range between 315 Hz to 5000 Hz. Especially in the range above 1000 Hz, the noise absorption coefficient α of the noise protection elements according to the invention is higher than in the case of the commercially available diesel box product.

The noise protection system Alpha has a particularly good noise absorption, but this product is technically complex and non-transparent.

Claims (13)

Noise protection element comprising a plate of a transparent material,
characterized in that
on at least one of the two surfaces of the plate, a noise absorbing material is applied. A noise barrier according to claim 1, wherein the transparent material comprises a polymer selected from polyalkyl (meth) acrylate, polycarbonate and polyalkyl (meth) acrylimide. A noise control element according to claim 1 or 2, wherein the transparent material comprises polymethyl methacrylate. Noise protection element according to at least one of the preceding claims, in which at least one of the two surfaces of the plate is at least partially frosted and / or the plate contains a particulate scattering agent. A noise control element according to any one of the preceding claims, wherein the noise absorbing material is a polymeric foam, preferably a polyolefin foam. Noise protection element according to at least one of the preceding claims, wherein the sound absorbing material on at least one side of the plate forms a regular or irregular pattern in the form of trees, shrubs, branches or geometric figures such as circles, triangles, rectangles or hexagons. Noise protection element according to at least one of the preceding claims, in which the sound-absorbing material is applied to at least one side of the plate in the form of a plurality of mutually parallel strips. The noise control element of at least one of the preceding claims, wherein the side of the panel to which a sound absorbing material is applied has a plurality of recesses at least partially covered and / or filled by the sound absorbing material. A noise control element according to claim 8, in which the recesses form a pattern of parallel straight lines extending across the entire surface of the plate. Noise protection element according to claim 8 or 9, in which the recesses have a triangular, trapezoidal, funnel-shaped, oval or rectangular cross-section. The noise control element of at least one of the preceding claims, wherein from 10% to 50% of at least one surface of the panel is covered by the sound absorbing material. Use of a noise protection element according to at least one of the preceding claims for noise insulation in a noise protection wall. Noise barrier wall for attenuating sound emissions of a traffic route, comprising the noise protection element according to at least one of claims 1-11, wherein the sound absorbing material is applied to a surface of the plate facing the traffic route of a transparent material.

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