| abstract |
Process for the production of polyurethane foams with a yellowness index less than 30, determined according to EN ISO 4892-2, and a tensile strength of at least 60 kPa, determined according to DIN 53571, by reaction of DOLLAR AA) at least one compound, the at least two compared to isocyanates contains reactive hydrogen atoms, with DOLLAR AB) at least one aliphatic or cycloaliphatic isocyanate, DOLLAR A, characterized in that the reaction is carried out in two stages by the prepolymer process, in which either DOLLAR A i) in a first stage the total amount of isocyanate B) with a subset of compound A) to form a prepolymer and in a second stage the prepolymer with the remaining amount of compound A) is converted to the finished polyurethane, DOLLAR A or DOLLAR A ii) in a first stage the total amount of compound A) with a subset of the isocyanate B) is converted into a prepolymer and in a second stage the prepolymer with the rest of the of the isocyanate B) is converted into the finished polyurethane. |