POLYURETHANE FOAMS WITH IMPROVED ACOUSTIC PROPERTIES

Abstract

The invention relates in a first aspect to a process for producing a polyurethane foam, comprising the reaction of (a) an isocyanate composition comprising at least one polyisocyanate based on diphenylmethane diisocyanate; (b) a polyol mixture, wherein the polyol mixture comprises (b1) 50% to 85% by weight of at least one polyether polyol having a hydroxyl value in the range from 10 to 60 mg KOH/g, an OH functionality of more than 2, and an ethylene oxide proportion in the range from 50% to 100% by weight based on the alkylene oxide content of the at least one polyether polyol, and (b2) 15% to 50% by weight of at least one polyether polyol having a hydroxyl value in the range from 10 to 100 mg KOH/g, an OH functionality of more than 2, an ethylene oxide proportion in the range from 2% to 30% by weight based on the alkylene oxide content of the at least one polyether polyol, and a proportion of primary OH groups of 40 to 100% based on the total number of OH groups in the at least one polyether polyol, in each case based on the total amount by weight of constituents (b1) and (b2), which adds up to 100% by weight, and (b3) 0 to 20 further parts by weight of an optionally derivatized filler, based on 100 parts by weight of components (b1) and (b2), optionally present as a constituent of a graft polyol based on one or more of components (b1) and (b2); (c) a blowing agent composition comprising water; wherein the reaction employs the blowing agent composition (c) in a weight-based ratio of the weight of blowing agent composition (c) to the total weight of all isocyanate-reactive compounds used in the reaction in the range from 1:14 to 1:6; wherein a polyurethane foam having a foam density, determined according to DIN EN ISO 845 (October 2009), of not more than 25 kg/m.sup.3 and a compression hardness, determined at 40% compression in the first compression in accordance with DIN EN ISO 3386-1 (October 2015), in the range from 10 to 80 kPa is obtained.

In a second aspect, the invention relates to a polyurethane foam obtained or obtainable by the process of the first aspect.

A third aspect of the invention relates to the use of a polyurethane foam according to the second aspect as a sound absorption material.

According to a fourth aspect, the invention relates to a sound absorption material comprising a polyurethane foam according to the second aspect, preferably consisting of a polyurethane foam according to the second aspect.

A fifth aspect of the invention relates to the use of a polyol mixture (b) comprising (b1), (b2), and (b3) as defined in the first aspect, for producing a polyurethane foam.

Claims

1.-15. (canceled)

16. A process for producing a polyurethane foam, comprising the reaction of: (a) an isocyanate composition comprising at least one polyisocyanate based on diphenylmethane diisocyanate; (b) a polyol mixture comprising b1) 50% to 85% by weight of at least one polyether polyol having a hydroxyl value in the range from 10 to 60 mg KOH/g, an OH functionality of more than 2, and an ethylene oxide proportion in the range from 50% to 100% by weight based on the alkylene oxide content of the at least one polyether polyol, b2) 15% to 50% by weight of at least one polyether polyol having a hydroxyl value in the range from 10 to 100 mg KOH/g, an OH functionality of more than 2, an ethylene oxide proportion in the range from 2% to 30% by weight based on the alkylene oxide content of the at least one polyether polyol, and a proportion of primary OH groups of 40 to 100% based on the total number of OH groups in the at least one polyether polyol, in each case based on the total amount by weight of constituents (b1) and (b2), which adds up to 100% by weight, and b3) 0 to 20 further parts by weight of an optionally derivatized filler, based on 100 parts by weight of components (b1) and (b2), optionally present as a constituent of a graft polyol based on one or more of components (b1) and (b2); (c) a blowing agent composition comprising water; wherein the reaction employs the blowing agent composition (c) in a weight-based ratio of the weight of blowing agent composition (c) to the total weight of all isocyanate-reactive compounds used in the reaction in the range from 1:14 to 1:6; wherein a polyurethane foam having a foam density, determined according to DIN EN ISO 845 of October 2009, of not more than 25 kg/m.sup.3 and a compression hardness, determined at 40% compression in the first compression in accordance with DIN EN ISO 3386-1 of October 2015, in the range from 10 to 80 kPa is obtained.

17. The process according to claim 16, wherein the polyol mixture (b) comprises the at least one polyether polyol (b1) in the range from 60% to 82% by weight, based on the total amount by weight of constituents (b1) and (b2), which adds up to 100% by weight; and/or wherein the polyol mixture (b) comprises the at least one polyether polyol (b2) in the range from 18% to 40% by weight, based on the total amount by weight of constituents (b1) and (b2), which adds up to 100% by weight.

18. The process according to claim 16, wherein the optionally derivatized filler according to (b3) is present as a constituent of a graft polyol based on a polyether polyol (b2), in an amount in the range from 0.01 to 20 further parts by weight, based on 100 parts by weight of components (b1) and (b2), and/or the filler according to (b3) is present as a dispersion in a polyether polyol (b2), in an amount in the range from 0.01 to 20 further parts by weight, based on 100 parts by weight of components (b1) and (b2).

19. The process according to claim 16, wherein the polyether polyol (b1) has an OH functionality in the range from 2.2 to 8; and/or wherein the polyether polyol (b1) has a proportion of primary OH groups in the range from 40 to 100%, based on the total number of OH groups in the polyether polyol (b1).

20. The process according to claim 16, wherein the polyether polyol (b2) has a proportion of primary OH groups in the range from 50 to 100%; and/or wherein the polyether polyol (b2) has an OH functionality in the range from 2.2 to 8.

21. The process according to claim 16, wherein the isocyanate composition (a) comprises in the range from 50% to 64% by weight, of 4,4′-diphenylmethane diisocyanate (4,4′-MDI), based on 100% by weight of isocyanate composition (a); and/or wherein the isocyanate composition (a) comprises in the range from 2% to 10% by weight of 2,4′-diphenylmethane diisocyanate (2,4′-MDI) based on 100% by weight of isocyanate composition (a).

22. The process according to claim 16, wherein the polyol mixture (b) further comprises: b4) at least one further polyether polyol that differs from the at least one polyether polyol according to (b1) and from the at least one polyether polyol according to (b2) and has a hydroxyl value of more than 350 mg KOH/g, in an amount in the range from 0 to 20 further parts by weight, based on 100 parts by weight of components (b1) and (b2).

23. The process according to claim 16, wherein the polyol mixture (b) comprises not more than 5 further parts by weight, based on 100 parts by weight of components (b 1) and (b2), of a further polyether polyol (b5), where (b5) has a hydroxyl value in the range from 10 to 100 mg KOH/g, an OH functionality of at least 2, an ethylene oxide proportion of 0% to 30% by weight based on the content of alkylene oxide, and a proportion of primary OH groups of 0 to 30% based on the total number of OH groups in the polyether polyol (b5).

24. The process according to claim 16, wherein the reaction employs the blowing agent composition (c) in a weight-based ratio to the total weight of all isocyanate-reactive compounds used in the reaction in the range from 1:12 to 1:7.

25. The process according to claim 16, wherein free-rise foaming is carried out.

26. A polyurethane foam obtained by the process according to claim 16.

27. The polyurethane foam according to claim 26, having an air permeability determined in accordance with DIN EN ISO 7231 of December 2010 of at least 0.02 dm.sup.3/s; and/or an air flow resistance (AFR) determined in accordance with DIN EN ISO 9053-1 of March 2019 of not more than 10 000 Pa.Math.s/m; and/or a compression hardness, determined at 40% compression in the first compression in accordance with DIN EN ISO 3386-1 of October 2015, in the range from 10 to 80 kPa; and/or a foam density, determined according to DIN EN ISO 845 of October 2009, of not more than kg/m.sup.3; and/or a resilience, determined according to DIN EN ISO 8307 of December 2018, in the range from 15 to 35%.

28. A method comprising utilizing the polyurethane foam according to claim 26 as a sound absorption material.

29. A sound absorption material comprising the polyurethane foam according to claim 26.

30. A method comprising utilizing a polyol mixture (b) comprising: b1) 50% to 85% by weight of at least one polyether polyol having a hydroxyl value in the range from 10 to 60 mg KOH/g, an OH functionality of more than 2, and an ethylene oxide proportion in the range from 50% to 100% by weight based on the alkylene oxide content of the at least one polyether polyol, b2) 15% to 50% by weight of at least one polyether polyol having a hydroxyl value in the range from 10 to 100 mg KOH/g, an OH functionality of more than 2, an ethylene oxide proportion in the range from 2% to 30% by weight based on the alkylene oxide content of the at least one polyether polyol, and a proportion of primary OH groups of 40 to 100% based on the total number of OH groups in the at least one polyether polyol, in each case based on the total amount by weight of constituents (b1) and (b2), which adds up to 100% by weight, and b3) 0 to 20 further parts by weight of an optionally derivatized filler, based on 100 parts by weight of components (b1) and (b2), optionally present as a constituent of a graft polyol based on one or more of components (b1) and (b2); for the production of a polyurethane foam, having at least one of the following properties: an air permeability determined in accordance with DIN EN ISO 7231 of December 2012 of at least 0.02 dm.sup.3/s; an air flow resistance (AFR) determined in accordance with DIN EN ISO 9053-1 of March 2019 of not more than 10 000 Pa.Math.s/m; a compression hardness, determined at 40% compression in the first compression in accordance with DIN EN ISO 3386-1 of October 2015, in the range from 10 to 80 kPa; a foam density, determined according to DIN EN ISO 845 of October 2009, of not more than 25 kg/m.sup.3; a resilience, determined according to DIN EN ISO 8307 of December 2018, in the range from 15 to 35%.

Description

EXAMPLES

1 Measurement Methods

[0191]

TABLE-US-00001 TABLE 1 Standards used for foam tests Property Unit Standard Year-month Foam density kg/m.sup.3 DIN EN ISO 845 2009 October Compression kPa DIN EN ISO 3386-1 2015 October hardness 40% (in first compression) Tensile strength kPa DIN EN ISO 1798 2008 April Elongation at break % DIN EN ISO 1798 2008 April Resilience % DIN EN ISO 8307 2018 December Air permeability dm.sup.3/s DIN EN ISO 7231 2010 December AFR* Pa .Math. s/m DIN EN ISO 9053-1 2019 March *Air flow resistance

2 Starting Materials

[0192] Polyol A: OH value 42 mg KOH/g, polyether alcohol having 77% primary OH groups based on propylene oxide and ethylene oxide (72% by weight), starter glycerol. The average functionality was 2.7.

[0193] Polyol B: OH value 29 mg KOH/g, polyether alcohol having 79% primary OH groups based on propylene oxide and ethylene oxide (14% by weight), starter glycerol. The average functionality was 2.7.

[0194] Polyol C: OH value 35 mg KOH/g, polyether alcohol having 72% primary OH groups based on propylene oxide and ethylene oxide (13% by weight), starter glycerol. The average functionality was 2.7.

[0195] Polyol D: OH value 20 mg KOH/g, graft polyol having a 45% content of filler (styrene-acrylonitrile, SAN), polyol C as carrier polyol. The average functionality was 2.7.

[0196] Polyol E: OH value 420 mg KOH/g, polyether alcohol based on propylene oxide (78% by weight), starter glycerol. The average functionality was 3.0.

[0197] DEOA: Diethanolamine 80% by weight in water

[0198] Sorbidex 70%: 70% by weight sorbitol in water

[0199] Jeffcat DPA: Amine catalyst (Huntsmann)

[0200] Kosmos 29: Tin catalyst (Evonik)

[0201] DABCO DC 198: Silicone stabilizer (Evonik)

[0202] Expandable graphite: Expandable (exfoliated) graphite

[0203] Exolit AP 422: Ammonium polyphosphate (Clariant)

[0204] Isocyanate A: NCO content 31.5% by weight, multiring diphenylmethane diisocyanate (multiring MDI) having a functionality of 2.7

[0205] Isocyanate B: NCO content 33.5% by weight, 4,4′-diphenylmethane diisocyanate (4,4′-MDI) (˜99% by weight)

[0206] Isocyanate C: NCO content 33.5% by weight, isomer mixture of 4,4′-MDI (˜50% by weight) and 2,4′-diphenylmethane diisocyanate (2,4′-MDI) (˜50% by weight)

3 Examples and Comparative Examples

[0207] Polyisocyanate compositions (a)-1 to (a)-4 were formed from isocyanates A, B, and C by mixing. Table 2 shows the composition of (a)-1 to (a)-4 in parts by weight or in % by weight calculated from the parts by weight of the respective polyisocyanate, based on 100% by weight of the polyisocyanate composition.

TABLE-US-00002 TABLE 2 Composition of the employed polyisocyanate composition (a)-1 to (a)-4 in parts by weight or in % by weight. Multiring 4,4'-MDI 2,4'-MDI MDI Isocyanate Isocyanate Isocyanate [% by [% by [% by A B C weight] weight] weight] Polyisocyanate 62.5 12.2 25.3 47.9 15.2 36.4 composition (a)-1 Polyisocyanate 72.5 21.4 6.1 51.3 6.4 42.2 composition (a)-2 Polyisocyanate 69.1 24.1 6.8 53.0 6.6 40.2 composition (a)-3 Polyisocyanate 65.6 26.8 7.6 54.7 6.9 38.2 composition (a)-4 Polyisocyanate 58.8 32.1 9.1 58.2 7.4 34.2 composition (a)-5

[0208] The starting materials were foamed to form a semi-rigid polyurethane foam in the amounts stated in Tables 3, 5, and 7 using water as the blowing agent.

[0209] For this, a mixture was in each case produced by mixing the specified polyols, catalysts, and additives. The respective mixture was mixed at the specified index with the polyisocyanate composition (a)-1 to (a)-4 or (a)-5 specified in the particular case, and placed in an open mold and left there for 24 hours. After 24 hours, the semi-rigid polyurethane foams obtained were sawn to obtain samples. All components were used at room temperature.

[0210] Tables 3, 5, and 7 show the amounts of polyols A-E used in parts by weight for each mixture plus, for components (b1) and (b2) of the polyol mixture (b) according to embodiment 1, the correspondingly calculated amounts in % by weight, based on the sum (b1)+(b2)=100% by weight, which are shown in the third-last and second-last rows respectively. In the form of a graft polyol with proportions of component (b2), optionally derivatized filler (b3) was present as a constituent of polyol D and the amount in parts by weight based on 100 parts by weight (b1)+(b2) is additionally shown in Tables 3 and 5, in the last row in each case.

[0211] The properties of the semi-rigid polyurethane foams thus obtained are given in Tables 4, 6, and 8 below. C1-C6 and C7-C9 were comparative examples, 1-12 and 13 to 17 represented examples according to the invention.

TABLE-US-00003 TABLE 3 Amounts used and constituents for production of the freely-foamed semi-rigid polyurethane foams (total weight of the employed components polyisocyanate composition, polyols, and additives approx. 1.3 kg). Amounts specified in parts by weight unless otherwise stated. C1 C2 C3 1 2 3 4 5 Polyol A 25 80 50 60 70 70 70 Polyol B 85 60 5 35 25 15 15 15 Polyol D 15 15 15 15 15 15 15 15 Polyol E 5 5 5 5 5 5 5 5 Polyisocyanate 0 0 0 0 0 0 147.8 0 composition (a)-1 Polyisocyanate 146.7 147.4 149.0 148.1 148.4 148.7 0 0 composition (a)-2 Polyisocyanate 0 0 0 0 0 0 0 148.1 composition (a)-4 DC 198 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 DEOA 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Jeffcat DPA 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Kosmos 29 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Water total* 10 10 10 10 10 10 10 10 Index 90 90 90 90 90 90 90 90 Polyol mixture (b) in % by weight based on (b1) + (b2) = 100% by weight: (b1) [% by weight] 0 26.8 85.8 53.6 64.3 75.1 75.1 75.1 (b2) [% by weight] 100 73.2 14.2 46.4 35.7 24.9 24.9 24.9 Further parts by 6.8 6.8 6.8 6.8 6.8 6.8 6.8 6.8 weight of filler SAN (b3) *“Water total” means the sum of added water and the water present in other components.

[0212] Foam C3 showed pronounced settling and could not be characterized.

TABLE-US-00004 TABLE 4 Mechanical properties of the semi-rigid foams obtained. C1 C2 C3 1 2 3 4 5 Foam density [kg/m.sup.3] 15.6 14.4 — 13.6 14.5 16.3 17.2 17.2 Compression hardness 35.5 24.1 — 19.7 20.9 29.0 23.5 27.0 40% [kPa] (in first compression) Tensile strength [kPa] 99 59 — 72 55 80 74 77 Elongation at break [%] 23 32 — 38 36 22 23 24 Resilience [%] 18 15 — 22 22 24 30 30 Air permeability [dm.sup.3/s] 0.004 0.007 — 0.063 0.027 0.168 0.147 0.318 AFR [Pa .Math. s/m] 59400 41700 — 2780 1200 813 1350 511 “—” Not determined

[0213] It was readily apparent that the inventive semi-rigid foams of examples 1 to 5 had considerably better acoustic properties in respect of sound absorption than comparative examples C1 to C3. For instance, the air permeability for the semirigid foams of examples 1 to 5, determined in accordance with DIN EN ISO 7231, was at least 0.02 dm.sup.3/s, whereas the semi-rigid foams of comparative examples C1 and C2 had air permeabilities of considerably less than 0.02 dm.sup.3/s. The inventive semi-rigid foams of examples 1 to 5 likewise had considerably better values in respect of air flow resistance, determined in accordance with DIN EN ISO 9053: 1-5 had AFR values of at most 10 000 Pa.Math.s/m, whereas C1 and C2 had AFR values of well above 10 000 Pa.Math.s/m, and in fact of well above 40 000 Pa.Math.s/m.

TABLE-US-00005 TABLE 5 Amounts used and constituents for production of the freely-foamed semi-rigid polyurethane foams (total weight of the employed components polyisocyanate composition, polyols/polyol mixture, and additives approx. 1.6 kg). Amounts specified in parts by weight unless otherwise stated. C4 C5 C6 6 7 8 9 10 11 12 Polyol A 0 25 80 50 60 70 70 70 70 75 Polyol B 85 60 5 35 25 15 15 15 30 25 Polyol D 15 15 15 15 15 15 15 15 0 0 Polyol E 5 0 5 5 5 5 5 5 5 5 Polyisocyanate 0 0 0 0 0 0 165.5 0 0 0 composition (a)-1 Polyisocyanate 164.9 165.3 167.0 167.1 166.8 166.6 0 0 166.8 166.7 composition (a)-2 Polyisocyanate 0 0 0 0 0 0 0 166.2 0 0 composition (a)-3 Expandable 20 20 20 20 20 20 20 20 20 20 graphite Exolit AP 422 5 5 5 5 5 5 5 5 5 5 DC 198 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Sorbidex 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 DEOA 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Jeffcat DPA 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Kosmos 29 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Water total* 12 12 12 12 12 12 12 12 12 12 Index 85 85 85 85 85 85 85 85 85 85 Polyol mixture (b) in % by weight based on (b1) + (b2) = 100% by weight: (b1) [% by weight] — 26.8 85.8 53.6 64.3 75.1 75.1 75.1 70.0 75.0 (b2) Polyol 100 73.2 14.2 46.4 35.7 24.9 24.9 24.9 30.0 25.0 mixture (b) in % by weight based on (b1) + (b2) = 100% by weight: Further parts 6.8 6.8 6.8 6.8 6.8 6.8 6.8 6.8 0 0 by weight of filler SAN (b3) *“Water total” means the sum of added water and the water present in other components.

[0214] Foam C5 had many cracks and could not be characterized, foam C6 showed pronounced settling and likewise could not be characterized.

TABLE-US-00006 TABLE 6 Mechanical properties of the semi-rigid foams obtained. C4 C5 C6 6 7 8 9 10 11 12 Foam density 16.9 — — 17.6 16.0 17.2 17.7 18.2 16.6 17.0 [kg/m.sup.3] Compression 33.5 — — 15.2 18.0 31.4 26.8 24.8 21.4 20.0 hardness 40% [kPa] (in first compression) Tensile strength 82 — — 35 35 72 69 55 58 62 [kPa] Elongation at 21 — — 34 24 18 17 17 26 21 break [%] Resilience [%] 15 — — 21 26 25 33 30 29 31 Air permeability 0.011 — — 0.265 0.274 0.288 0.219 0.46 0.322 0.382 [dm.sup.3/s] AFR [Pa .Math. s/m] 11600 — — 499 359 449 543 246 397 237 “—” Not determined

[0215] Even with the use of flame retardants, in this case expandable graphite, it was readily apparent that the inventive semi-rigid foams of examples 6 to 10 had considerably better acoustic properties in respect of sound absorption than comparative example C4. Comparative examples C5 and C6 could not be characterized at all, because of cracking or deposits. For instance, the air permeability for the semirigid foams of examples 6 to 10, determined in accordance with DIN EN ISO 7231, was at least 0.02 dm.sup.3/s, whereas the semi-rigid foam of comparative example C4 had air permeabilities of considerably less than 0.02 dm.sup.3/s. The inventive semi-rigid foams of examples 6 to 10 likewise had considerably better values in respect of air flow resistance, determined in accordance with DIN EN ISO 9053: 6-10 had AFR values of at most 10 000 Pa.Math.s/m, and in fact of less than 1000 Pa.Math.s/m, whereas C4 had an AFR value of well above 10 000 Pa.Math.s/m, and in fact of well above 11 000 Pa.Math.s/m.

TABLE-US-00007 TABLE 7 Amounts used and constituents for production of the freely-foamed semi-rigid polyurethane foams (total weight of the employed components polyisocyanate composition, polyols/polyol mixture, and additives approx. 1.6 kg). Amounts specified in parts by weight unless otherwise stated. C7 C8 C9 13 14 15 16 17 Polyol A 25 50 70 70 70 70 Polyol B 85 85 60 35 15 15 15 15 Polyol D 15 15 15 15 15 15 15 15 Polyol E 5 5 5 5 5 5 5 5 Polyisocyanate 0 0 0 0 140.9 0 0 0 composition (a)-1 Polyisocyanate 139.9 0 140.6 141.2 0 141.8 0 0 composition (a)-2 Polyisocyanate 0 0 0 0 0 0 141.2 0 composition (a)-4 Polyisocyanate 0 138.8 0 0 0 0 0 140.6 composition (a)-5 Expandable graphite 20 20 20 20 20 20 20 20 Exolit AP 422 5 5 5 5 5 5 5 5 DC 198 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Sorbidex 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 DEOA 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Jeffcat DPA 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Kosmos 29 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Water total* 10 10 10 10 10 10 10 10 Index 85 85 85 85 85 85 85 85 Polyol mixture (b) in % by weight based on (b1) + (b2) = 100% by weight: (b1) [% by weight] 0 0 26.8 53.6 75.1 75.1 75.1 75.1 (b2) Polyol mixture (b) in % 100 100 73.2 46.4 24.9 24.9 24.9 24.9 by weight based on (b1) + (b2) = 100% by weight: Further parts by weight of 6.8 6.8 6.8 6.8 6.8 6.8 6.8 6.8 filler SAN (b3) *“Water total” means the sum of added water and the water present in other components.

[0216] Foam C8 had many cracks and could not be characterized.

TABLE-US-00008 TABLE 8 Mechanical properties of the semi-rigid foams obtained. C7 C8 C9 13 14 15 16 17 Foam density [kg/m.sup.3] 18.3 — 17.0 16.7 18.1 18.1 18.4 18.6 Compression hardness 31.6 — 18.5 15.1 20.6 21.3 21.5 20.1 40% [kPa] (in first compression) Tensile strength [kPa] 77 — 66 50 64 63 60 70 Elongation at break [%] 27 — 30 38 25 22 22 24 Resilience [%] 18 — 21 26 27 26 26 29 Air permeability [dm.sup.3/s] 0.008 — 0.009 0.046 0.207 0.139 0.334 0.668 AFR [Pa .Math. s/m] 22300 — 33100 2610 579 546 361 200 “—” Not determined

[0217] By comparison, the inventive semi-rigid foams of examples 13-17 likewise showed considerably better acoustic properties in respect of sound absorption than comparative examples C7 and C9. Comparative example C8 could not be characterized at all, because of cracking. For instance, the air permeability for the semirigid foams of examples 13 to 17, determined in accordance with DIN EN ISO 7231, was at least 0.02 dm.sup.3/s, whereas the semi-rigid foam of comparative examples C7 and C9 had air permeabilities of considerably less than 0.02 dm.sup.3/s. The inventive semi-rigid foams of examples 13 to 17 likewise had considerably better values in respect of air flow resistance, determined in accordance with DIN EN ISO 9053: 13-17 had AFR values of well below 10 000 Pa.Math.s/m, whereas C7 and C9 had AFR values of well above 10 000 Pa.Math.s/m, and in fact of well above 10 000 Pa.Math.s/m. Within the inventive semi-rigid foams of examples 14-17, it was also evident that the composition of the polyisocyanate mixture had an effect: For instance, whereas example 14, which had been produced with polyisocyanate composition (a)-1 (less than 50% by weight of 4,4′-MDI and more than 10% by weight of 2,4′-MDI, in each case based on 100% by weight of polyisocyanate composition), had a good AFR value, the AFR values of examples 15, 16, and 17, in which the polyisocyanate composition in each case comprised more than 50% by weight of 4,4′-MDI and less than 10% by weight of 2,4′-MDI, in each case based on 100% by weight of the polyisocyanate composition, were by comparison even more considerably improved, and were below 200 Pa s/m, preferably below 100 Pa s/m.

[0218] The comparison with comparative example C8, which had a suitable polyisocyanate composition (a)-5, but not in combination with a suitable polyol mixture, showed that the effect of the composition of the polyisocyanate mixture had shown synergy only with the polyol mixture—foam C8 had many cracks and could not be characterized.

CITED LITERATURE

[0219] WO 2019/002013 A1

[0220] EP 1 664 147 B1

[0221] EP 2 800 770 B2

[0222] EP 1 230 297 B1

[0223] WO 2009/003964 A1

[0224] WO 2009/138379 A1

[0225] “Dow Polyurethanes Flexible Foams”, 2nd edition 1997, chapter 2.

[0226] DE 4318120 A1

[0227] WO 2006/034800 A1

[0228] “Kunststoffhandbuch” [Plastics handbook], volume 7, “Polyurethane” [Polyurethanes], Carl Hanser Verlag, 3rd edition, 1993, chapter 3.1

[0229] DE 10314762 A1

[0230] “Kunststoffhandbuch” [Plastics handbook], volume 7, “Polyurethane” [Polyurethanes], Carl Hanser Verlag, 3rd edition, 1993, chapter 3.4