WO2022185275A1

WO2022185275A1 - Acoustic damper material

Info

Publication number: WO2022185275A1
Application number: PCT/IB2022/051938
Authority: WO
Inventors: Giovanni BERTOLAJA
Original assignee: Becchis Osiride S.R.L.
Priority date: 2021-03-05
Filing date: 2022-03-04
Publication date: 2022-09-09
Also published as: EP4302292B1; EP4302292C0; IT202100005210A1; PL4302292T3; EP4302292A1

Abstract

A highly effective acoustic damper comprising Poaceae powder, preferably bamboo or giant bamboo is described. Preferably, more than 50% of the powder is made up of particles having a size comprised between 100 and 500 mesh and is added in a percentage comprised between 10% by weight and 50% by weight with respect to the total weight of the acoustic damper.

Description

ACOUSTIC DAMPER MATERIAL

CROSS-REFERENCE TO RELATED APPLICATIONS

This Patent Application claims priority from Italian Patent Application No. 102021000005210 filed on March 5, 2021, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a highly effective acoustic damper comprising Poaceae powder (Bambusoideae), in particular, to an acoustic damper of the type in sheets.

STATE OF THE PRIOR ART

As is known, acoustic dampers generally consist of viscoelastic materials of a macromolecule-based amorphous nature. Viscoelastic materials have a very high elasticity modulus at low temperature and are thus in the glassy state. As the temperature increases, the elasticity modulus progressively decreases to the glass transition temperature. The elasticity factor is directly linked to the loss factor or internal damping, also indicated by the Greek letter h. Such internal damping is linked to the acoustic behaviour, i.e. to the damping ability of the vibrations having a wavelength in the range of human hearing. In fact, damping indicates the ability of a material to attenuate the vibrational motion to which it is subjected.

In order to improve the damping and thus the absorbing behaviour of the vibrations of the aforementioned materials, the glass transition temperature of the viscoelastic materials is, for example, lowered.

Among the acoustic dampers, the ones comprising bitumen as a viscoelastic material are known. In particular, various resins can be added to such dampers as additives. In order to further improve the damping characteristics, it is also known to add lamellar fillers such as mica or graphite to the dampers.

Many researches are under way for further increasing the damping power with fillers similar to the lamellar ones, but no one has yet found the right materials for such purpose.

OBJECT OF THE INVENTION

The object of the present invention is to provide an acoustic damper with improved damping properties.

According to the present invention, such object is achieved by an acoustic damper according to claim 1.

DESCRIPTION OF THE INVENTION

Within the scope of the present invention, an acoustic damper is understood to be a compound comprising a viscoelastic material suitable for absorbing the vibrations having a wavelength in the range of human hearing, in other words for attenuating the vibrational motion to which it is subjected.

Acoustic dampers are used, for example, for the treatment of surfaces subjected to vibrations. Such acoustic dampers are usable, for example, in the doors or on the body bottom of vehicles, but also for the acoustic treatment of household appliances.

The acoustic dampers of the present invention can be manufactured in the form of sheets, or in paste, for applications on surfaces subjected to vibrations.

Bituminous material or distilled bitumen is understood to be a viscoelastic material consisting of distillation residues of crude oil.

Within the scope of the present invention, distilled bitumen is understood to be a colloidal dispersion of asphaltenic particles from 5% to 25 by weight with respect to the total weight of the dispersion in a continuous oily step consisting of oils and resins (maltenes).

The used distilled bitumen preferably has penetration degrees comprised between 20/30 and 50/70, more preferably for example: 20/30 or 35/50 or 50/70, which characterize the hardness of the material.

Higher penetration values indicate a softer consistency of the bitumen.

Fillers are understood to be substances of various nature which can optionally be added to the viscoelastic materials in order to improve the chemical and physical characteristics of the acoustic dampers.

The acoustic dampers provided according to the present invention comprise at least one viscoelastic material having a high internal damping. The viscoelastic material is a bituminous material.

The acoustic damper can also comprise fillers such as, for example, at least one mineral filler selected from the group consisting of talc, calcium carbonate, coal ash or biomass ash, in a variable quantity from 10% to 60%.

Optionally, the acoustic damper can also comprise lamellar fillers such as for example graphite or mica.

Optionally, the acoustic damper can also further comprise plasticizers or oils of natural origin or other polymers such as, for example, SBR or PP, preferably in a quantity comprised between 1 and 10%, more preferably in a quantity comprised between 1% and 3% by weight.

The provided acoustic damper further comprises Poaceae powder, preferably the Poaceae are Bambusoideae. More preferably, the Bambusoideae are bamboo or giant bamboo.

Preferably, more than 50% of the powder is made up of particles having a size smaller than 500 mesh, preferably between 100 and 500 mesh, even more preferably comprised between 120 and 325 mesh.

Preferably, the powder is added directly to the viscoelastic material.

The natural bamboo powder does not undergo the carbonization process. Preferably, it has a water content comprised between 1 and 10% by weight, more preferably 5% and 7%.

Advantageously, the powder derives from grinding and is added in percentages comprised between 5% and 60% by weight, more preferably between 10% and 50% by weight with respect to the weight of the acoustic damper.

When added in such proportions, the powder allows obtaining an increase in the damping as shown in the examples presented in the following.

The acoustic dampers of the present invention can advantageously be used in the form of calendered sheets or as template die-cut calendered sheets. The coupling to the surface to be treated can be made by means of heating in an oven or by means of self-adhesive glues.

The acoustic dampers are applied, for example, inside vehicles.

For example, they can be made adhesive to the body of the vehicle.

Alternatively, they can be used in household appliances. For example, in dishwashers, 90% of the machine can be covered with bituminous acoustic dampers.

The acoustic dampers preferably have a density comprised between 0.70 and 1.60 g/ml, more preferably between 0.95 and 1.45 g/ml. Since the Poaceae powder conducts heat relatively poorly, it has also been proven that the acoustic dampers of the present invention have a reduced thermal conductivity with respect to other known fillers and preferably comprised between 0.258 and 0.384 W/mK, which is an advantage in particular when the acoustic dampers of the present invention are used in household appliances, for example for the thermoacoustic treatment of dishwashers.

The advantages of the acoustic dampers provided according to the present invention are evident from the foregoing description; in particular, it has been proven that the addition of Poaceae powder allows obtaining an increase in the elastic modulus of the acoustic damper and thus a corresponding increase in the damping ability, and at the same time also allows obtaining lighter acoustic dampers, thanks to the lower density of the powder with respect to the fillers.

Finally, the addition of the Poaceae powder (Bambusoideae) is very advantageous from the environmental point of view, since it is a plant species that grows back quickly, thus the indefinite reforestation is ensured. The Poaceae (Bambusoideae) are a grass, not a wood species, and thanks to this characteristic thereof, they have a lighter impact on the environment. It is known that they capture five times more Co2 than the young forests, producing an extra 35% of oxygen.

It is thus particularly advantageous to use the Poaceae powder instead of the known lamellar fillers.

The invention will be described in the following referring to examples, without thereby being limited thereto.

Examples of fillers usable for improving the damping characteristics of a viscoelastic material and providing an acoustic damper according to the known art and according to the present invention are listed in Table 1, where it can be observed that, while the average size of the Poaceae powder particles is similar to that of the particles of the known fillers, the density instead is much lower, thus allowing obtaining acoustic dampers on the whole lighter. Table 1

EXAMPLES 1-2 Table 2 shows the examples 1 to 2 of compositions of acoustic dampers provided according to the known art, whereas Table 3 shows the examples 3 to 6 of acoustic dampers provided according to the invention. Table 2

Table 3

Density measurement tolerance: ± 0.03

Thermal conductivity measurement tolerance: ± 0.01

Damping measurement tolerance: ± 0.02

The density is calculated based on ISO 1183-1:2019 Plastics - Methods for determining the density of non- cellular plastics Immersion method, liquid pycnometer method and titration method.

Following this method, the density is calculated from the hydrostatic thrust. The hydrostatic thrust method prevents the problem of determining the volume because it requires for the sample to be weighed twice in two different media (air and a liquid). The volume can thus be considered constant in both situations. The volume of a solid sample is determined by observing the increase in the level of the liquid in which the sample is immersed. The pycnometer is first weighed empty and then filled with the reference liquid of known density. The sample is inserted in the clean and dry pycnometer. The weight of the sample is determined in this way. The pycnometer is then filled with the same liquid and weighed again. In this way, it is possible to determine the weight of the shifted liquid and thus calculate the density of the sample.

The thermal conductivity test is conducted for each value on three samples according to the standard UNI EN 12664:2002, Thermal performance of building materials and products, through the determination of the thermal resistance with the guard ring hot plate method and with the heat flow meter method and ASTM E1530:2019, Standard test method for evaluating the resistance to the thermal transmission by means of a flow meter. The standards establish the methods for determining the thermal values of the design and of the ASTM standard, on which the operating principle of the used measurement apparatus is based. The latter implements the method with a heat flow meter and guard ring, which allows the determination, indirectly and subject to calibration procedure of the instrument, of the thermal conductivity. The determination is indirect since the conductivity is achieved via the direct detection of the heat flow along a test stack, inside which the specimen is inserted, which recreates the ideal, stable and one dimensional heat exchange conditions. The flow, in turn, is determined thanks to the measurement of the thermal jumps on the specimen and on a reference material that constitutes the heat flow meter (heat flow sensor).

The calibration, instead, is carried out on a series of reference specimens of known and attested thermal characteristics and allows tracing the unknown conductivity of the material being tested by exploiting the definition of thermal resistance R_s (m²K/W), as expressed in the equation below, which is precisely a function of the thickness s of the specimen and of the thermal conductivity l (W/mK): R_s = S/ l

Where:

Rs = Thermal resistance (m²K/W) s = sample thickness (m); l = thermal conductivity of the specimen (W/mK) As far as the damping is concerned, the data are obtained by following the most common method standardized according to ASTM E 756-05 Standard Test Method for Measuring Vibration-Damping Properties of Materials.

In particular, the elastic modulus and the intrinsic damping of the damping materials are determined by means of the ASTM procedure based on an experiment conducted on material samples with a variable frequency and temperature.

The material samples to be analysed must be mounted on a steel bar so as to guide their vibration and allow the identification of vibrational peaks and modal shapes. The excitation and the measurement must be conducted by means of contactless transducers so as not to alter the mass and the stiffness of the sample to be measured. The sample must be excited by means of a random function or a sweep at a constant amplitude over the entire frequency spectrum of interest. The result of the experiment consists in a frequency response function of the sample to the variation of the temperature. From the frequency response functions, it is possible to extract the modal resonance peaks of the coupled system (metal bar - damping material) and extract the typical frequency and damping. Once these data have been obtained, the standard allows determining the elastic modulus and the intrinsic damping values of the damping material by means of specific formulations (paragraph 10 of the standard), excluding the contribution of the support used for the tests. All the data obtained in this way can then be grouped into a frequency response nomogram called the "Master Curve". Starting from the Master Curve, it is possible to estimate the behaviour of the damping material following its application on any type of flat support.

The penetration test is conducted on three samples of bitumen, according to the standard ASTM D5/D5M - 20.

The sample of distilled bitumen is brought to 190 °C and left in the furnace until it melts. The melted material is subsequently poured into a disposable baking cup (diameter approx. 60-80 mm) and left for 24 hours to solidify. The baking cup is placed on a flat surface and left untouched, so that the surface of the solidified sample remains free of ripples and slopes.

After 24 hours, the baking cup is completely immersed in a thermostatic bath at 25°C for 2 hours. In the meantime, the instrument is prepared. The penetrometer consists of a metal arm connected to a support bar that allows it to vertically slide in order to adjust its height. At the base of the arm there is a cavity in which, by means of a screw, it is possible to fix a removable needle. At the top there is the dial which allows reading the penetration of the needle in the sample expressed in dmm. The range of the instrument is 360 dmm and the sensitivity is 1 dmm. At the base of the instrument there is the electronic device consisting of the rest plane of the sample and which is connected to the movable arm, which is released for the time required to carry out the measurement (5 ± 1 s) when the measurement is initiated. Mount one of the needles, cleaned with acetone, at the base of the arm. Set the needle of the dial to zero. Remove the sample from the bath, dry it and position it in the rest base of the instrument. Bring the needle down to just above the surface of the sample so that the tip is positioned at a point at least 10 mm away from the edge of the baking cup. Gradually lower the needle with the knob placed on the support bar, until the tip joins with its image reflected on the surface of the sample.

Start the measurement, when the test is finished, the height of the arm will have decreased by a certain amount depending on the depth of penetration. The needle of the dial will have shifted giving a measurement in dmm of how much the needle penetrated inside the sample.

When the reading is finished, remove the needle from the measurement arm and mount a clean needle. Conduct three measurements on the same sample. The points at which the measurement is conducted must be at least 10 mm spaced from one another and in turn at least 10 mm spaced from the edge of the baking cup. Calculate the arithmetic mean of the three results obtained and express them in dmm.

Claims

1.- Acoustic damper comprising distilled bitumen, characterized in that it comprises a Poaceae powder of a size comprised between 100 and 500 mesh.

2 . - Acoustic damper according to claim 1, characterized in that said Poaceae are Bambusoideae.

3.- Acoustic damper according to claim 1, characterized in that said Bambusoideae are bamboo or giant bamboo.

4 .- Acoustic damper according to claim 1 or 2, characterized in that more than 50% of said powder is made up of particles having a size between 120 and 325 mesh.

5 .- Acoustic damper according to any one of the preceding claims, characterized in that it comprises a filler selected from the group consisting of talc, shale, calcium carbonate, graphite or mica or a substance selected from the group consisting of plasticizers, oils of natural origin, SBR and PP.

6.- Acoustic damper according to any one of the preceding claims, characterized in that said powder is added in a percentage comprised between 10% by weight and 50% by weight with respect to the total weight of the acoustic damper.

7 .- Process for manufacturing an acoustic damper according to any one of claims 1 to 6, characterized in that it comprises a step of adding a Bambusoideae powder to a viscoelastic material.

8.- Process for manufacturing an acoustic damper according to claim 7, characterized in that it comprises a step of calendering in sheets.

9.- Use of acoustic dampers according to any one of claims 1 to 6, in the form of calendered sheets.

10 .- Use of acoustic dampers according to claim 9 in the form of template die-cut sheets.

11 . - Use of acoustic dampers according to any one of claims 1 to 6, in household appliances or in a form that is made adhesive to the internal body of vehicles.