POLYURETHANE FOAMS WITH IMPROVED ACOUSTIC PROPERTIES

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/m3 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