WO2024115593A1

WO2024115593A1 - Sound absorbing structure

Info

Publication number: WO2024115593A1
Application number: PCT/EP2023/083595
Authority: WO
Inventors: Lisa Marie Schmidt; Elmar Poeselt; Theresa HUELSMANN; Frank THIELBEER; Ulrike GROENHAGEN; Holger Schrovenwever
Original assignee: Basf Se
Priority date: 2022-11-30
Filing date: 2023-11-29
Publication date: 2024-06-06

Abstract

The present invention is directed to a sound absorbing structure comprising a foam material, wherein the foam material is an elastomer with a closed surface and the free volume of the material is below 10%, in particular wherein the foam material comprises foamed pellets and the free volume of the material between the foamed pellets is below 10%. The present invention also relates to the use of a foam material comprising foamed pellets for the preparation of a sound absorbing structure.

Description

I nfinergy for acoustic applications

The present invention relates to a sound absorbing structure which has open voids and good sound absorbing qualities in a wide frequency range, and possesses sound absorbing qualities useful for floor backing materials, wall backing materials and core materials thereof, automotive interior materials, or the like.

Foams, especially particle foams, have long been known and have been widely described in the literature, e.g. in Ullmann's "Encyclopedia of Technical Chemistry", 4th edition, volume 20, p.

416 ff.

Highly elastic, largely closed-cell foams, such as particle foams made of thermoplastic elastomers, which e.g. produced in an autoclave or by the extruder process show special dynamic properties and in some cases also good rebound resilience. Hybrid foams made from particles of thermoplastic elastomers and system foam or binders are also known. Depending on the foam density, the manufacturing method and the matrix material, a relatively broad level of rigidity can be adjusted. The properties of the foam can also be influenced by post-treatment of the foam, such as tempering.

Foamed pellets, which are also referred to as particle foams (or bead foams, particle foam), and molded articles made therefrom, based on thermoplastic polyurethane or other elastomers, are known (for example WO 94/20568A1 , WO 2007/082838 A1 , WO2017/030835 A1 , WO 2013/153190 A1 , WO2010/010010 A1 ) and can be used in many different ways.

A foamed pellet or also a particle foam or bead foam in the sense of the present invention refers to a foam in the form of a particle, the average length of the particles preferably being in the range of from 1 to 8 mm. In the case of non-spherical, e.g. elongated or cylindrical particles mean the longest dimension by length.

Various applications are known for foamed pellets and molded bodies prepared from the foamed pellets.

Japanese Patent Application Laid-Open Nos. 137063/1995 and 108441/1996 describe the fact that expansion-molded articles with open voids obtained by molding foamed particles of a specific shape have sound absorbing qualities. These publications describe the expansion-molded articles as having excellent sound absorbing qualities, but this only means that the molded articles have excellent sound absorbing qualities in a narrow acoustic frequency range of specific wavelengths.

However, there is still a need for materials with a good sound absorption coefficient in a wide acoustic frequency range.

It was therefore an object of the present invention to provide sound absorbing martials which can be used in a wide acoustic frequency range and preferably materials which can be easily prepared and adjusted in shape

According to the present invention, this object is solved by a sound absorbing structure comprising a foam material, wherein the foam material is an elastomer with a closed surface and the free volume of the material is below 10%.

It was surprisingly found that that elastomeric foam materials with a closed surface and the free volume of the material below 10% show very good properties as sound absorbing materials.

According to the present invention, the sound absorbing structure may also be a molded body.

According to the present invention, a molded body or molded article may for example be obtained by bonding small resin pieces or foamed pellets so as to form a molded body with a free volume which is formed between the particles or pellets.

The foam material is an elastomer with a closed surface. According to the present invention, a closed surface means that the cell structure of the foam material is preferably completely closed. The closed cell structure may for example be determined by the water absorption. Preferably, the water absorption of the foam material is below 5%, more preferably below 4% when the material is brought into contact with water for up to 10 seconds, for example for 5 to 10 seconds.

The free volume according to the present invention is below 10%. The free volume A (%) of the material is calculated in accordance with the following equation:

A(%)=[(B-C)/B]*100 wherein B is the apparent volume (cm³) of the molded article of the resin particles, and C is the true volume (cm³) of the molded article of the resin particles. The apparent volume B is a volume calculated out from the outside dimensions of the molded article, and the true volume C is a volume of the molded article found from an increased volume determined by sinking the molded article into a graduated cylinder containing water. The free volume of the foam material according to the present invention is below 10%, preferably in a range of from 1 to 8%, in particular in a range of from 2 to 6% in view of sound absorbing qualities and stability to formation of open voids.

As described above, the material according to the present invention has excellent sound absorbing qualities, can exhibit a sufficient function even in the form of a simple material in an application field of sound absorption and sound insulation and moreover can be applied to other wide uses such as combinations with other sound absorbing materials. The sound absorbing structure according to the present invention can be produced by a molding process comprising filling foamed pellets into a mold and heating them, thereby integrally fusion-bonding the foamed pellets to one another. According to a further embodiment, the present invention is also directed to a sound absorbing structure as disclosed above, wherein the foam material comprises foamed pellets.

According to the present invention, the sound absorbing properties are determined using the impedance tube measurement according to ISO 10534-2. Preferably, the sound absorbing structure according to the present invention has an increased noise absorption at 500 - 2000 Hz.

According to a further embodiment, the present invention is directed to the process as disclosed above, wherein the average length of the foamed pellets is in the range of from 1 to 8 mm, preferably in the range of from 1 to 6, in particular in the range of from 2 to 6, more preferable in the range of from 3 to 5.

According to a further embodiment, the present invention is also directed to a sound absorbing structure as disclosed above, wherein the foamed pellets have a particle size in the range of from 1 to 15 mm, for example 1 to 8 mm.

It has been found that materials having good mechanical properties and good sound absorbing properties can be obtained by using fused foamed pellets as a foam material. Preferably, the foamed pellets have a closed surface and the free volume of the material is formed by the free volume between the foamed pellets. Therefore, according to a further embodiment, the present invention is also directed to a sound absorbing structure as disclosed above, wherein the free volume of the material between the foamed pellets is below 10%. In this case, the free volume determined according to the equation:

A(%)=[(B-C)/B]*100 is the free volume between the foamed pellets. Preferably, the free volume between the foamed pellets is h in a range of from 1 to 8%, in particular in a range of from 2 to 6%.

Processes for producing foamed ppellets are in principle known to the person skilled in the art. The shape of the pellets used according to the present invention may vary. It is possible to use rounded, non-spherical, e.g. elongated or cylindrical particles as well as pellets with e.g. flatted surface spots.

The shape and dimensions of the foamed pellets in the molded body may differ from the shape and dimensions of the foamed pellets used in the process due to the process conditions. It is for example possible that rounded foamed pellets are used in the process and the foamed pellets in the molded body have a rounded, non-spherical shape, e.g. elongated or cylindrical pellets as well as pellets with e.g. flatted surface spots. The average length of the foamed pellets in the molded body may for example be in the range of from 1 to 15 mm, preferably 1 to 8 mm. In the case of non-spherical, e.g. elongated or cylindrical particles mean the longest dimension by length.

Fusing the foamed pellets is preferably carried out in a mold to shape the molded body obtained. In principle, all suitable methods for fusing foamed pellets can be used according to the present invention, for example fusing at elevated temperatures, such as for example steam chest molding, molding at high frequencies, for example using electromagnetic radiation, processes using a double belt press, or variotherm processes.

According to a further embodiment, the present invention is also directed to a sound absorbing structure as disclosed above, wherein the foam material comprises a polymer material selected from the group consisting of thermoplastic elastomers.

Processes for producing foamed pellets from thermoplastic elastomers are also known per se to the person skilled in the art. If, according to the invention, a foamed granulate made of the thermoplastic elastomer is used, the bulk density of the foamed granulate is, for example, in the range from 20 g/l to 300 g/l.

Preferably, the thermoplastic elastomer has a soft phase with a glass transition temperature T_g in the range of from <10 °C determined by dynamic mechanical thermal analysis determined by loss factor (tan 5) according to DIN EN ISO 6721-1-2011-08 at a heating rate of 2 K/min at a frequency of 1 Hz in torsion mode. Deviant from the DIN norm, the temperature was adjusted step wise by 5 K and 35 s per step which corresponds to a continuous heating rate of 2 K/min. The measurements were conducted with a sample with a ratio of width: thickness of 1 :6. The sample was prepared by injection moulding followed by annealing of the material at 100 °C for 20 h.

Therefore, according to a further embodiment, the present invention is also directed to the sound absorbing structure as disclosed above, wherein the thermoplastic elastomer has a soft phase with a glass transition temperature T_g in the range of from < 10 °C more preferable below -10°C, particularly preferred below -30°C determined by dynamic mechanical thermal analysis determined by loss factor (tan 5) according to DIN EN ISO 6721-1-2011-08 at a heating rate of 2 K/min at a frequency of 1 Hz in torsion mode. Deviant from the DIN norm, the temperature was adjusted step wise by 5 K and 35 s per step which corresponds to a continuous heating rate of 2 K/min. The measurements were conducted with a sample with a ratio of width: thickness of 1 :6. The sample was prepared by injection moulding followed by annealing of the material at 100 °C for 20 h.

According to a further embodiment, the present invention is directed to the molded body as disclosed above, wherein the thermoplastic elastomer has a soft phase with a glass transition temperature T_g in the range of from < 10 °C determined by dynamic mechanical thermal analysis determined by loss factor (tan 5) according to DIN EN ISO 6721-1-2011-08 at a heating rate of 2 K/min at a frequency of 1 Hz in torsion mode. Deviant from the DIN norm, the temperature was adjusted step wise by 5 K and 35 s per step which corresponds to a continuous heating rate of 2 K/min. The measurements were conducted with a sample with a ratio of width: thickness of 1 :6. The sample was prepared by injection moulding followed by annealing of the material at 100 °C for 20 h.

According to a further embodiment, the present invention is also directed to a sound absorbing structure as disclosed above, wherein the polymer material has a TG of the soft phase of less than -10°C, determined by dynamic mechanical thermal analysis determined by loss factor (tan 5) according to DIN EN ISO 6721-1-2011-08 at a heating rate of 2 K/min at a frequency of 1 Hz in torsion mode, for example in the range of from -70°C, in particular in the range of from - 40°C to -10°C

Suitable thermoplastic elastomers for producing the foams or moldings according to the invention are known per se to the person skilled in the art. Suitable thermoplastic elastomers are described, for example, in “Handbook of Thermoplastic Elastomers”, 2nd edition June 2014. For example, the thermoplastic elastomer can be a thermoplastic polyurethane (TPU), a thermoplastic polyether amide (TPA), a polyether ester (TPC), a polyester ester (TPC), a thermoplastic elastomer based on olefin (TPO), a crosslinked thermoplastic elastomer based on olefin or a thermoplastic vulcanizate (TPV) or a thermoplastic styrene butadiene block copolymer (TPS), in particular selected from the group consisting of thermoplastic polyurethanes, thermoplastic polyamides and thermoplastic polyester elastomers.

According to a further embodiment, the present invention is also directed to a sound absorbing structure as disclosed above, wherein the foam material comprises a polymer material selected from the group consisting of thermoplastic polyurethanes, thermoplastic polyamides and thermoplastic polyester elastomers. Particularly suitable thermoplastic elastomers are thermoplastic polyurethanes.

Suitable production processes for these thermoplastic elastomers or foams or foamed pellets from the thermoplastic elastomers mentioned are likewise known to the person skilled in the art. Suitable thermoplastic polyether esters and polyester esters can be prepared by all the conventional processes known from the literature by transesterification or esterification of aromatic and aliphatic dicarboxylic acids having 4 to 20 carbon atoms or their esters with suitable aliphatic and aromatic diols and polyols (cf. “Polymer Chemistry “, Interscience PubL, New York, 1961 , p.111-127; Kunststoff Handbuch, Volume VIII, C. Hanser Verlag, Munich 1973 and Journal of Polymer Science, Part A1 , 4, pages 1851-1859 (1966)).

Preferably, the foam materials according to the present invention have a density of less than 280 g/l.

According to a further embodiment, the present invention is also directed to a sound absorbing structure as disclosed above, wherein the foam material has a density of less than 280 g/l, for example in the range of from 50 to 280 g/l.

The thermoplastic polyetheramides can be obtained by the reaction of amines and carboxylic acids or their esters by all of the methods known from the literature. Amines and or carboxylic acid also contain ether units of the type R-O-R, where R = organic radical (aliphatic and I or aromatic). In general, monomers of the following classes of compounds are used: HOOC-R'-NH2, where R 'can be aromatic and aliphatic, preferably containing ether units of the type R-O-R, where R = organic radical (aliphatic and I or aromatic); aromatic dicarboxylic acids, e.g. Phthalic acid, isophthalic acid and terephthalic acid or their esters and aromatic dicarboxylic acids containing ether units of the type R-O-R, where R = organic radical (aliphatic and I or aromatic); aliphatic dicarboxylic acids, e.g. Cyclohexane-1 ,4-dicarboxylic acid, adipic acid, sebacic acid, azelaic acid and decanedicarboxylic acid as saturated dicarboxylic acids as well as maleic acid, fumaric acid, aconitic acid, itaconic acid, tetrahydrophthalic acid and tetrahydroterephthalic acid as unsaturated as well as aliphatic dicarboxylic acids R = containing organic units, R being ether units, ether units can be aliphatic and I or aromatic); Diamines of the general formula H2N-R " - NH2, where R " is aromatic and aliphatic, preferably containing ether units of the type R-O-R, where R = organic radical (aliphatic and I or aromatic); Lactams such as e-caprolactam, pyrrolidone or laurolactam; as well as amino acids.

The thermoplastic elastomers with block copolymer structure used according to the invention preferably contain vinylaromatic, butadiene and isoprene as well as polyolefin and vinyl units, for example ethylene, propylene & vinyl acetate units. Styrene-butadiene copolymers are preferred.

Suitable olefin-based thermoplastic elastomers (TPO) in particular have a hard segment and a soft segment, the hard segment being, for example, a polyolefin such as polypropylene and polyethylene and the soft segment being a rubber component such as ethylene-propylene rubber. Blends of a polyolefin and a rubber component, dynamically cross-linked types and polymerized types are suitable. According to a further embodiment, the present invention is directed to the process as disclosed above, wherein the thermoplastic elastomer is selected from the group consisting of thermoplastic polyurethanes.

Also thermoplastic polyurethanes are well known. They are produced by reaction of isocyanates with isocyanate-reactive compounds for example polyols with number-average molar mass from 500 g/mol to 100 00 g/mol and optionally chain extenders with molar mass from 50 g/mol to 499 g/mol, optionally in the presence of catalysts and/or conventional auxiliaries and/or additional substances.

For the purposes of the present invention, preference is given to thermoplastic polyurethanes obtainable via reaction of isocyanates with isocyanate-reactive compounds for example polyols with number-average molar mass from 500 g/mol to 10000 g/mol and a chain extender with molar mass from 50 g/mol to 499 g/mol, optionally in the presence of catalysts and/or conventional auxiliaries and/or additional substances.

The isocyanate, isocyanate-reactive compounds for example polyols and, if used, chain extenders are also, individually or together, termed structural components. The structural components together with the catalyst and/or the customary auxiliaries and/or additional substances are also termed starting materials.

The molar ratios of the quantities used of the polyol component can be varied in order to adjust hardness and melt index of the thermoplastic polyurethanes, where hardness and melt viscosity increase with increasing content of chain extender in the polyol component at constant molecular weight of the TPU, whereas melt index decreases.

For production of the thermoplastic polyurethanes, isocyanates and polyol component, where the polyol component in a preferred embodiment also comprises chain extenders, are reacted in the presence of a catalyst and optionally auxiliaries and/or additional substances in amounts such that the equivalence ratio of NCO groups of the diisocyanates to the entirety of the hydroxyl groups of the polyol component is in the range from 1 :0.8 to 1 :1.3.

Another variable that describes this ratio is the index. The index is defined via the ratio of all of the isocyanate groups used during the reaction to the isocyanate-reactive groups, i.e. in particular the reactive groups of the polyol component and the chain extender. If the index is 1000, there is one active hydrogen atom for each isocyanate group. At indices above 1000, there are more isocyanate groups than isocyanate-reactive groups.

An equivalence ratio of 1 :0.8 here corresponds to an index of 1250 (index 1000 = 1 :1 ), and a ratio of 1 :1 .3 corresponds to an index of 770. In a preferred embodiment, the index in the reaction of the abovementioned components is in the range from 965 to 1110, preferably in the range from 970 to 1110, particularly preferably in the range from 980 to 1030, and also very particularly preferably in the range from 985 to 1010.

Preference is given in the invention to the production of thermoplastic polyurethanes where the weight-average molar mass (M_w) of the thermoplastic polyurethane is at least 60 000 g/mol, preferably at least 80 000 g/mol and in particular greater than 100 000 g/mol. The upper limit of the weight-average molar mass of the thermoplastic polyurethanes is very generally determined by processibility, and also by the desired property profile. The number-average molar mass of the thermoplastic polyurethanes is preferably from 80 000 to 300 000 g/mol. The average molar masses stated above for the thermoplastic polyurethane, and also for the isocyanates and polyols used, are the weight averages determined by means of gel permeation chromatography (e.g. in accordance with DIN 55672-1 , March 2016).

Organic isocyanates that can be used are aliphatic, cycloaliphatic, araliphatic and/or aromatic isocyanates.

Aliphatic diisocyanates used are customary aliphatic and/or cycloaliphatic diisocyanates, for example tri-, tetra-, penta-, hexa-, hepta- and/or octamethylene diisocyanate, 2-methylpentameth- ylene 1 ,5-diisocyanate, 2-ethyltetramethylene 1 ,4-diisocyanate, hexamethylene 1 ,6-diisocya- nate (HDI), pentamethylene 1 ,5-diisocyanate, butylene 1 ,4-diisocyanate, trimethylhexamethylene 1 ,6-diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 1 ,4- and/or 1 ,3-bis(isocyanatomethyl)cyclohexane (HXDI), cyclohexane 1 ,4-diisocyanate, 1 -methylcyclohexane 2,4- and/or 2, 6-diisocyanate, methylenedicyclohexyl 4,4'-, 2,4'- and/or 2,2'-diisocyanate (H12MDI).

Suitable aromatic diisocyanates are in particular naphthylene 1 ,5-diisocyanate (NDI), tolylene 2,4- and/or 2, 6-diisocyanate (TDI), 3,3’-dimethyl-4,4‘-diisocyanatobiphenyl (TODI), p-phenylene diisocyanate (PDI), diphenylethane 4,4‘-diisoyanate (EDI), methylenediphenyl diisocyanate (MDI), where the term MDI means diphenylmethane 2,2’, 2,4’- and/or 4, 4’-diisocyanate, 3,3’-di- methyldiphenyl diisocyanate, 1 ,2-diphenylethane diisocyanate and/or phenylene diisocyanate.

Mixtures can in principle also be used. Examples of mixtures are mixtures comprising at least a further methylenediphenyl diisocyanate alongside methylenediphenyl 4,4’-diisocyanate. The term “methylenediphenyl diisocyanate” here means diphenylmethane 2,2’-, 2,4’- and/or 4,4’- diisocyanate or a mixture of two or three isomers. It is therefore possible to use by way of example the following as further isocyanate: diphenylmethane 2,2’- or 2,4’-diisocyanate or a mixture of two or three isomers. In this embodiment, the polyisocyanate composition can also comprise other abovementioned polyisocyanates.

Other examples of mixtures are polyisocyanate compositions comprising 4,4‘-MDI and 2,4‘- MDI, or 4,4‘-MDI and 3,3‘-dimethyl-4,4‘-diisocyanatobiphenyl (TODI) or 4,4‘-MDI and H12MDI (4,4'-methylene dicyclohexyl diisocyanate) or 4,4‘-MDI and TDI; or 4,4‘-MDI and 1 ,5-naph- thylene diisocyanate (NDI).

In accordance with the invention, three or more isocyanates may also be used. The polyisocyanate composition commonly comprises 4,4’-MDI in an amount of from 2 to 50%, based on the entire polyisocyanate composition, and the further isocyanate in an amount of from 3 to 20%, based on the entire polyisocyanate composition.

Crosslinkers can be used as well, moreover, examples being the aforesaid higher-functionality polyisocyanates or polyols or else other higher-functionality molecules having a plurality of iso- cyanate-reactive functional groups. It is also possible within the realm of the present invention for the products to be crosslinked by an excess of the isocyanate groups used, in relation to the hydroxyl groups. Examples of higher-functionality isocyanates are triisocyanates, e.g. triphenylmethane 4,4',4"-triisocyanate, and also isocyanurates, and also the cyanurates of the aforementioned diisocyanates, and the oligomers obtainable by partial reaction of diisocyanates with water, for example the biurets of the aforementioned diisocyanates, and also oligomers obtainable by controlled reaction of semiblocked diisocyanates with polyols having an average of more than two and preferably three or more hydroxyl groups.

The amount of crosslinkers here, i.e. of higher-functionality isocyanates and higher-functionality polyols, ought not to exceed 3% by weight, preferably 1 % by weight, based on the overall mixture of components.

The polyisocyanate composition may also comprise one or more solvents. Suitable solvents are known to those skilled in the art. Suitable examples are nonreactive solvents such as ethyl acetate, methyl ethyl ketone and hydrocarbons.

Isocyanate-reactive compounds are those with molar mass M_n that is preferably from 500 g/mol to 10000 g/mol, more preferably from 500 g/mol to 5000 g/mol, in particular from 500 g/mol to 3000 g/mol.

The statistical average number of hydrogen atoms exhibiting Zerewitinoff activity in the isocyanate-reactive compound is at least 1 .8 and at most 2.2, preferably 2; this number is also termed the functionality of the isocyanate-reactive compound (b), and states the quantity of isocyanatereactive groups in the molecule, calculated theoretically for a single molecule, based on a molar quantity. The isocyanate-reactive compound preferably is substantially linear and is one isocyanate-reactive substance or a mixture of various substances, where the mixture then meets the stated requirement.

The ratio of polyols and chain extender used is varied in a manner that gives the desired hard- segment content, which can be calculated by the formula disclosed in WO 2018/087362. A suitable hard segment content here is below 60%, preferably below 40%, particularly preferably 25%. The isocyanate-reactive compound preferably has a reactive group selected from the hydroxyl group, the amino groups, the mercapto group and the carboxylic acid group. Preference is given here to the hydroxyl group and very particular preference is given here to primary hydroxyl groups. It is particularly preferable that the isocyanate-reactive compound (b) is selected from the group of polyesterols, polyetherols and polycarbonatediols, these also being covered by the term “polyols”.

Suitable polymers in the invention are homopolymers, for example polyetherols, polyesterols, polycarbonatediols, polycarbonates, polysiloxanediols, polybutadienediols, and also block copolymers, and also hybrid polyols, e.g. poly(ester/amide). Preferred polyetherols in the invention are polyethylene glycols, polypropylene glycols, polytetramethylene glycol (PTHF), polytrimethylene glycol. Preferred polyester polyols are polyadipates, polysuccinic esters and polycaprolactones.

In another embodiment, the present invention also provides a thermoplastic polyurethane as described above where the polyol composition comprises a polyol selected from the group consisting of polyetherols, polyesterols, polycaprolactones and polycarbonates.

Examples of suitable block copolymers are those having ether and ester blocks, for example polycaprolactone having polyethylene oxide or polypropylene oxide end blocks, and also polyethers having polycaprolactone end blocks. Preferred polyetherols in the invention are polyethylene glycols, polypropylene glycols, polytetramethylene glycol (PTHF) and polytrimethylene glycol. Preference is further given to polycaprolactone.

In a particularly preferred embodiment, the molar mass Mn of the polyol used is in the range from 500 g/mol to 10000 g/mol, preferably in the range from 500 g/mol to 5000 g/mol, in particular from 500 g/mol to 3000 g/mol.

Another embodiment of the present invention accordingly provides a thermoplastic polyurethane as described above where the molar mass Mn of at least one polyol comprised in the polyol composition is in the range from 500 g/mol to 10000 g/mol.

It is also possible in the invention to use mixtures of various polyols.

An embodiment of the present invention uses, for the production of the thermoplastic polyurethane, at least one polyol composition comprising at least polytetrahydrofuran. The polyol composition in the invention can also comprise other polyols alongside polytetrahydrofuran.

Materials suitable by way of example as other polyols in the invention are polyethers, and also polyesters, block copolymers, and also hybrid polyols, e.g. poly(ester/amide). Examples of suitable block copolymers are those having ether and ester blocks, for example polycaprolactone having polyethylene oxide or polypropylene oxide end blocks, and also polyethers having polycaprolactone end blocks. Preferred polyetherols in the invention are polyethylene glycols and polypropylene glycols. Preference is further given to polycaprolactone as other polyol.

Examples of suitable polyols are polyetherols such as polytrimethylene oxide and polytetramethylene oxide.

Another embodiment of the present invention accordingly provides a thermoplastic polyurethane as described above where the polyol composition comprises at least one polytetrahydrofuran and at least one other polyol selected from the group consisting of another polytetramethylene oxide (PTHF), polyethylene glycol, polypropylene glycol and polycaprolactone.

In a particularly preferred embodiment, the number-average molar mass Mn of the polytetrahydrofuran is in the range from 500 g/mol to 5000 g/mol, more preferably in the range from 550 to 2500 g/mol, particularly preferably in the range from 650 to 2000 g/mol and very preferably in the range from 650 to 1400 g/mol.

The composition of the polyol composition can vary widely for the purposes of the present invention. By way of example, the content of the first polyol, preferably of polytetrahydrofuran, can be in the range from 15% to 85%, preferably in the range from 20% to 80%, more preferably in the range from 25% to 75%.

The polyol composition in the invention can also comprise a solvent. Suitable solvents are known per se to the person skilled in the art.

Insofar as polytetrahydrofuran is used, the number-average molar mass Mn of the polytetrahydrofuran is by way of example in the range from 500 g/mol to 5000 g/mol, preferably in the range from 550 to 2500 g/mol, particular preferably in the range from 650 to 2000 g/mol. It is further preferable that the number-average molar mass Mn of the polytetrahydrofuran is in the range from 650 to 1400 g/mol.

The number-average molar mass Mn here can be determined as mentioned above by way of gel permeation chromatography.

Another embodiment of the present invention also provides a thermoplastic polyurethane as described above where the polyol composition comprises a polyol selected from the group consisting of polytetrahydrofurans with number-average molar mass Mn in the range from 500 g/mol to 5000 g/mol preferably in the range from 550 to 2500 g/mol, particular preferably in the range from 650 to 2000 g/mol. It is further preferable that the number-average molar mass Mn of the polytetrahydrofuran is in the range from 650 to 1400 g/mol.

It is also possible in the invention to use mixtures of various polytetrahydrofurans, i.e. mixtures of polytetrahydrofurans with various molar masses. Chain extenders used are preferably aliphatic, araliphatic, aromatic and/or cycloaliphatic compounds with a molar mass from 50 g/mol to 499 g/mol, preferably having 2 isocyanate-reactive groups, also termed functional groups. Preferred chain extenders are diamines and/or alkanediols, more preferably alkanediols having from 2 to 10 carbon atoms, preferably having from 3 to 8 carbon atoms in the alkylene moiety, these more preferably having exclusively primary hydroxy groups.

Preferred embodiments use chain extenders, these being preferably aliphatic, araliphatic, aromatic and/or cycloaliphatic compounds with molar mass from 50 g/mol to 499 g/mol, preferably having 2 isocyanate-reactive groups, also termed functional groups. It is preferable that the chain extender is at least one chain extender selected from the group consisting of ethylene 1 ,2-glycol, propane-1 ,2-diol, propane-1 ,3-diol, butane-1 ,4-diol, butane-2,3-diol, pentane-1 ,5-diol, hexane-1 ,6-diol, diethylene glycol, dipropylene glycol, cyclohexane-1 ,4-diol, cyclohexane-1 ,4- dimethanol, neopentyl glycol and hydroquinone bis(beta-hydroxyethyl) ether (HQEE). Particularly suitable chain extenders are those selected from the group consisting of 1 ,2-ethanediol, propane-1 ,3-diol, butane-1 ,4-diol and hexane-1 ,6-diol, and also mixtures of the abovementioned chain extenders. Examples of specific chain extenders and mixtures are disclosed inter alia in WO 2018/087362.

In preferred embodiments, catalysts are used with the structural components. These are in particular catalysts which accelerate the reaction between the NCO groups of the isocyanates and the hydroxyl groups of the isocyanate-reactive compound and, if used, the chain extender.

Examples of catalysts that are further suitable are organometallic compounds selected from the group consisting of organyl compounds of tin, of titanium, of zirconium, of hafnium, of bismuth, of zinc, of aluminum and of iron, examples being organyl compounds of tin, preferably dialkyltin compounds such as dimethyltin or diethyltin, or tin-organyl compounds of aliphatic carboxylic acids, preferably tin diacetate, tin dilaurate, dibutyltin diacetate, dibutyltin dilaurate, bismuth compounds, for example alkylbismuth compounds or the like, or iron compounds, preferably iron(lll) acetylacetonate, or the metal salts of carboxylic acids, e.g. tin(ll) isooctanoate, tin dioctanoate, titanic esters or bismuth(lll) neodecanoate. Particularly preferred catalysts are tin dioctanoate, bismuth decanoate and titanic esters. Quantities preferably used of the catalyst are from 0.0001 to 0.1 part by weight per 100 parts by weight of the isocyanate-reactive compound. Other compounds that can be added, alongside catalysts, to the structural components are conventional auxiliaries. Mention may be made by way of example of surface-active substances, fillers, flame retardants, nucleating agents, oxidation stabilizers, lubricating and demolded body aids, dyes and pigments, and optionally stabilizers, preferably with respect to hydrolysis, light, heat or discoloration, inorganic and/or organic fillers, reinforcing agents and/or plasticizers.

Suitable dyes and pigments are listed at a later stage below. Stabilizers for the purposes of the present invention are additives which protect a plastic or a plastics mixture from damaging environmental effects. Examples are primary and secondary antioxidants, sterically hindered phenols, hindered amine light stabilizers, UV absorbers, hydrolysis stabilizers, quenchers and flame retardants. Examples of commercially available stabilizers are found in Plastics Additives Handbook, 5th edn., H. Zweifel, ed., Hanser Publishers, Munich, 2001 ([1]), pp. 98-136.

The thermoplastic polyurethanes may be produced batchwise or continuously by the known processes, for example using reactive extruders or the belt method by the “one-shot” method or the prepolymer process, preferably by the “one-shot” method. In the “one-shot” method, the components to be reacted, and in preferred embodiments also the chain extender in the polyol component, and also catalyst and/or additives, are mixed with one another consecutively or simultaneously, with immediate onset of the polymerization reaction. The TPU can then be directly pelletized or converted by extrusion to lenticular pellets. In this step, it is possible to achieve concomitant incorporation of other adjuvants or other polymers.

In the extruder process, structural components, and in preferred embodiments also the chain extender, catalyst and/or additives, are introduced into the extruder individually or in the form of mixture and reacted, preferably at temperatures of from 100°C to 280°C, preferably from 140°C to 250°C. The resultant polyurethane is extruded, cooled and pelletized, or directly pelletized by way of an underwater pelletizer in the form of lenticular pellets.

In a preferred process, a thermoplastic polyurethane is produced from structural components isocyanate, isocyanate-reactive compound including chain extender, and in preferred embodiments the other raw materials in a first step, and the additional substances or auxiliaries are incorporated in a second extrusion step.

It is preferable to use a twin-screw extruder, because twin-screw extruders operate in force-conveying mode and thus permit greater precision of adjustment of temperature and quantitative output in the extruder. Production and expansion of a TPU can moreover be achieved in a reactive extruder in a single step or by way of a tandem extruder by methods known to the person skilled in the art.

The sound absorbing structure according to the present invention may also comprise mixtures of two or more elastomers or also mixtures of an elastomer and a further polymer such as for example polystyrene, polyethylene, polypropylene, polyethylene terephthalate, polycarbonates, polyamides, polybutylene terephthalate, polyethylene terephthalates and polylactic acids.

The sound absorbing structure according to the present invention comprising a foam material, wherein the foam material is an elastomer with a closed surface and the free volume of the material is below 10%. The foam material may be present in the sound absorbing structure in form of a layer or may also be embedded in a further material. The sound absorbing structure according to the present invention may also comprise further layers, in particular further layers with sound absorbing properties or further layers which provide a specific shape or stabilize the sound absorbing structure.

According to a further embodiment, the present invention is also directed to a sound absorbing structure as disclosed above, wherein the sound absorbing structure comprises further layers.

According to a further aspect, the present invention is also directed to the use of a foam material comprising foamed pellets for the preparation of a sound absorbing structure. A foam material comprising foamed pellets may for example be used in various use applications such as sound absorbing materials in residences, composite materials with building materials in road, aeronautical navigation, rail road, architecture and the like, soundproofing panels for constructional equipment in buildings, and automotive structural materials such as interior materials and bumpers or also musical instruments.

According to a further aspect, the present invention is also directed to the use of a sound absorbing structure as disclosed above for the preparation of a musical instrument, paneling for floors and walls, construction elements such as window frames, insulating elements or sliding gates, elements for constructing walls, floors, ceilings or doors.

The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The ... of any one of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The ... of any one of embodiments 1 , 2, 3, and 4". Further, it is explicitly noted that the following set of embodiments is not the set of claims determining the extent of protection, but represents a suitably structured part of the description directed to general and preferred aspects of the present invention.

1 . A sound absorbing structure comprising a foam material, wherein the foam material is an elastomer with a closed surface and the free volume of the material is below 10%.

2. The sound absorbing structure according to embodiment 1 , wherein the foam material comprises foamed pellets.

3. The sound absorbing structure according to embodiment 2, wherein the foamed pellets have a particle size in the range of from 1 to 15 mm. 4. The sound absorbing structure according to any one of embodiments 2 or 3, wherein the free volume of the material between the foamed pellets is below 10%.

5. The sound absorbing structure according to any one of embodiments 1 to 4, wherein the foam material comprises a polymer material selected from the group consisting of thermoplastic elastomers.

6. The sound absorbing structure according to any one of embodiments 1 to 5, wherein the foam material comprises a polymer material selected from the group consisting of thermoplastic polyurethanes, thermoplastic polyamides and thermoplastic polyester elastomers.

7. The sound absorbing structure according to any one of embodiments 1 to 6, wherein the foam material has a density of less than 280 g/l.

8. The sound absorbing structure according to any one of embodiments 1 to 7, wherein the polymer material has a TG of the soft phase of less than -10°C, determined by dynamic mechanical thermal analysis determined by loss factor (tan 5) according to DIN EN ISO 6721-1-2011-08 at a heating rate of 2 K/min at a frequency of 1 Hz in torsion mode.

9. The sound absorbing structure according to any one of embodiments 1 to 8, wherein the sound absorbing structure comprises further layers.

10. The use of a foam material comprising foamed pellets for the preparation of a sound absorbing structure.

11 . The use of a sound absorbing structure according to any one of embodiments 1 to 9 for the preparation of a musical instrument, paneling for floors and walls, construction elements such as window frames, insulating elements or sliding gates, elements for constructing walls, floors, ceilings or doors.

12. A sound absorbing structure comprising a foam material, wherein the foam material is an elastomer with a closed surface and the free volume of the material is below 10% and the foam material comprises a polymer material selected from the group consisting of thermoplastic polyurethanes.

13 The sound absorbing structure according to embodiment 12, wherein the foam material comprises foamed pellets.

14. The sound absorbing structure according to embodiment 13, wherein the foamed pellets have a particle size in the range of from 1 to 15 mm. 15. The sound absorbing structure according to any one of embodiments 13 or 14, wherein the free volume of the material between the foamed pellets is below 10%.

16. The sound absorbing structure according to any one of embodiments 12 to 15, wherein the foam material has a density of less than 280 g/l.

17. The sound absorbing structure according to any one of embodiments 12 to 16, wherein the polymer material has a TG of the soft phase of less than -10°C, determined by dynamic mechanical thermal analysis determined by loss factor (tan 5) according to DIN EN ISO 6721-1-2011-08 at a heating rate of 2 K/min at a frequency of 1 Hz in torsion mode.

18. The sound absorbing structure according to any one of embodiments 12 to 17, wherein the sound absorbing structure comprises further layers.

19. The use of a sound absorbing structure according to any one of embodiments 12 to 18 for the preparation of a musical instrument, paneling for floors and walls, construction elements such as window frames, insulating elements or sliding gates, elements for constructing walls, floors, ceilings or doors.

20. The use of a foam material comprising foamed pellets for the preparation of a sound absorbing structure.

21 . The use according to embodiment 20, wherein the foamed pellets have a particle size in the range of from 1 to 15 mm.

22. The use according to any one of embodiments 20 or 21 , wherein the free volume of the material between the foamed pellets is below 10%.

23. The use according to any one of embodiments 20 to 22, wherein the foam material comprises a polymer material selected from the group consisting of thermoplastic elastomers.

24. The use according to any one of embodiments 20 to 23, wherein the foam material comprises a polymer material selected from the group consisting of thermoplastic polyurethanes, thermoplastic polyamides and thermoplastic polyester elastomers.

25. The use according to any one of embodiments 20 to 24, wherein the foam material has a density of less than 280 g/l.

26. The use according to any one of embodiments 20 to 25, wherein the polymer material has a TG of the soft phase of less than -10°C, determined by dynamic mechanical thermal analysis determined by loss factor (tan 5) according to DIN EN ISO 6721-1-2011-08 at a heating rate of 2 K/min at a frequency of 1 Hz in torsion mode. The present invention is further illustrated by the following reference examples, comparative examples, and examples.

Examples

1. Materials used

1.1 The synthesis of the TPU 1 precursor was carried out using a 48D (12 zones) twin-screw- extruder (ZSK58 MC, co. Coperion). The temperature of the extruder housing I zones was between 150 to 230 °C and a screw-speed of 180 to 240 1/min at a through-put of 180 - 220 kg/h. In the first zone the polyol, chain extender, catalyst and diisocyanate was added. Further additives were added in zone 8. The formulation is listed in table 1.

After a gear pump and a melt filter the polymer melt at 180-210 °C was granulated using an underwater granulation. The granulate was subsequently dried using a heating fluidized bed (40-90 °C).

Table 1: Formulation of the used precursor.

1.2. eTPU 1 preparation

The manufacturing of E-TPU 1 was carried out on a twin screw extruder (Berstorff ZE 40) having a screw diameter of 44 mm and a L/D of 48, followed by a melt pump, a starting valve with screen changer, a die plate and an underwater pelletizer. The TPU was predried according to the processing guide at 80 °C for 3 hours for a residual humidity lower than 0,02 wt. %.

After the dosing, the material was molten and mixed in the extruder and afterwards a mixture of CO2 and N2 was added as blowing agents. In the remaining extruder barrels, the polymer and the blowing agents were mixed into a homogenous mixture. The mixture is pressed by a melt pump to a starting valve including screen changer and finally through a die plate into the water box of an underwater pelletizing system. There the mixture is cut to granulates, and foamed in the pressurized, tempered water system. The water flow transports the beads to a centrifuge dryer where they are separated from the water stream. The total throughput was set to 40 kg/h (including polymers, blowing agents).

1 .3 Generation of thermoplastic polyurethane (TPU2) as precursor for expanded thermoplastic polyurethane particles (eTPU2)

TPU which serves as precursor for the was produced by means of a twin-screw extruder ZSK 58MC with a length of 48D of the company Coperion. After the twin screw extruder, a melt pump, a melt filter, and an underwater cutting system were arranged within the mentioned sequence. The melt was cut into single compact particles of 40 mg using the underwater pelletizing system and the particles dried at 40 - 90 °C using a heated fluidized bed.

The polyol, the isocyanate as well as the chain extender were added in the first barrel section of the twin screw extruder, further additives followed in barrel section 8 out of 12. The used TPU recipe is shown in Table 2.

The barrel temperature was set to 180 - 230 °C while the resulting melt temperature was in the range of 210 - 230 °C at a screw speed of 180 to 240 rpm. The overall throughput during the TPU production was 200 kg/h.

Table 2

1 .4 Foaming of TPU 2

TPU 2 was foamed according to W02007/082838 using a stirred, heated, and pressurized vessel. For this purpose, 100 parts of TPU 2, 217 parts of water based on the amount of TPU 2 and 36 parts of blowing agent n-butane based on the amount of TPU 2 were added into the pressure vessel. The mixture was heated up to 109 °C while steering constantly. After reaching 109 °C, the temperature was kept constant for 60 min to enable a full impregnation of the compact beads with the blowing agent. Afterwards, the impregnated TPU beads with water and the remaining blowing agent were let out of the vessel by opening a valve at the bottom of the vessel. To avoid a sudden pressure drop within the vessel and to hold a constant high pressure level, the vessel was pressure loaded with nitrogen from the top of the vessel.

The impregnated particles expanded due to the pressure drop while entering the vessel through the bottom valve and, afterwards, were dried at about 50 °C in a heated fluidized bed.

The expanded beads (eTPU 2) obtained via the above method show a fine cell structure characterized by average cell size in the range of 10 - 40 pm and a bulk density of 83 g/l.

The average cell size was measured using a SEM (scanning electron microscope) picture combined with an image analysis software based on Image J. The software measures the area of the cells within the SEM picture. Afterwards the determined cell-area is converted in a notional circle with the same area and the diameter of the circle taken as the diameter of the cell. To calculate the average cell diameter, the procedure is applied for at least 100 different cells and the average value is calculated.

The bulk density was measured according to DIN EN ISO 60:1999. In difference to the standard, a bucket with a volume of 10 I was measured instead of 100 ml. The funnel was placed above the bucket in a distance of 100 mm from the lower end of the funnel to the upper end of the bucket. The funnel had an inner diameter of 300 mm on the top and 50 mm on the bottom where the expanded beads escape to fall into the bucket. Examples

To describe the effect of the given invention, the applied measurement system is the impedance tube measurement according to ISO 10534-2. Therefore, samples with the dimension of 100 mm diameter and a thickness of 20 mm are prepared mechanically out of sample plates.

The test method covered in the ISO 10534-2 the use of an impedance tube, where a sound source is located on one side and the test sample on the other side. Two defined microphone locations and a digital frequency analysis system for the determination of the acoustical sound absorption ratio of materials. The test samples must be placed accurately without any compression in the impedance tube.

As test samples were used the material Basotect from BASF as reference for open cell acoustic foam. In comparison of the closed cell eTPU samples 1 and 2, there are two closed cell examples without specific acoustic capabilities. These are Neopolen P (from BASF) and a closed cell foam MC1590 from FCI, Japan. Sample size for this measurement are two samples of each material.

The results of the acoustic absorption properties are listed in table 3 and show the in- creased noise absorption at the eTPU samples 1 & 2 at 500 - 2000 Hz.

Table 3: Results of Impedance tube measurement

The good values of the eTPU samples are even reached at closed surface and with blem- ishes of the closed surface <3%. To rate the closed surface, the same samples are compared in a water absorption test.

All samples are weighed at dry condition before the test. Afterwards the samples are placed into a basin which contain 1 I of water for 30 s. All samples were weighted down by a piece of metal with 200g weight, to insure a complete covering of the samples with water. After 30s the samples are released from the basin and be dabbed gently on the outer surface and weighed again. The measured water content represents the grade of open cell structure. All the weight measurements are done with a Mettler Toledo PG503-S weighing device and the sample size are two samples of each material.

Table 4: Results of water absorption test

Literature cited:

WO 94/20568A1

WO 2007/082838 A1

WO2017/030835 A1

WO 2013/153190 A1

WO2010/010010 A1

JP 137063/1995

JP 108441/1996

WO 2018/087362 A1

Ullmann's "Encyclopedia of Technical Chemistry", 4th edition, volume 20, p. 416 ff

Polymer Chemistry “, Interscience PubL, New York, 1961 , p.111-127; Kunststoff Handbuch, Volume VIII, C. Hanser Verlag, Munich 1973 and Journal of Polymer Science, Part A1 , 4, pages 1851-1859 (1966)

Plastics Additives Handbook, 5th edn., H. Zweifel, ed., Hanser Publishers, Munich, 2001 ([1]), pp. 98-136

Claims

2. The sound absorbing structure according to claim 1 , wherein the free volume A (%) of the material is calculated in accordance with the following equation:

A(%)=[(B-C)/B]*100 wherein B is the apparent volume (cm³) of the molded article of the resin particles, and C is the true volume (cm³) of the molded article of the resin particles.

3. The sound absorbing structure according to any one of claims 1 or 2, wherein the foam material comprises foamed pellets.

4. The sound absorbing structure according to claim 3, wherein the foamed pellets have a particle size in the range of from 1 to 15 mm.

5. The sound absorbing structure according to any one of claims 3 or 4, wherein the free volume of the material between the foamed pellets is below 10%.

6. The sound absorbing structure according to any one of claims 1 to 5, wherein the water absorption of the foam material is below 5%, when the material is brought into contact with water for up to 10 seconds.

7. The sound absorbing structure according to any one of claims 1 to 6, wherein the free volume of the material is in a range of from 2 to 6%.

8. The sound absorbing structure according to any one of claims 1 to 7, wherein the foam material comprises a polymer material selected from the group consisting of thermoplastic elastomers.

9. The sound absorbing structure according to any one of claims 1 to 8, wherein the foam material comprises a polymer material selected from the group consisting of thermoplastic polyurethanes, thermoplastic polyamides and thermoplastic polyester elastomers.

10. The sound absorbing structure according to any one of claims 1 to 9, wherein the foam material has a density of less than 280 g/l . The sound absorbing structure according to any one of claims 1 to 10, wherein the polymer material has a TG of the soft phase of less than -10°C, determined by dynamic mechanical thermal analysis determined by loss factor (tan 5) according to DIN EN ISO 6721-1-2011-08 at a heating rate of 2 K/min at a frequency of 1 Hz in torsion mode. The sound absorbing structure according to any one of claims 1 to 11 , wherein the sound absorbing structure comprises further layers. The use of a foam material comprising foamed pellets for the preparation of a sound ab- sorbing structure. The use of a sound absorbing structure according to any one of claims 1 to 12 for the preparation of a musical instrument, paneling for floors and walls, construction elements such as window frames, insulating elements or sliding gates, elements for constructing walls, floors, ceilings or doors.