| 摘要 |
A process for preparing a polyurethane material having no glass transition temperature below 25~C, which process comprises reacting a polyisocyanate an d an isocyanate-reactive composition, optionally in the presence of water in a n amount of less than 5 % by weight on the below isocyanate-reactive composition, wherein the reaction is conducted at an isocyanate index of 80 to 140, the polyisocyanate consists of a) 80-100 % by weight of diphenylmethane diisocyanate comprising at least 40 %, preferably at least 60 % and most preferably at least 85% by weight of 4,4'-diphenylmethane diisocyanate and/o r a variant of said diphenylmethane diisocyanate which variant is liquid at 25 ~C and has an NCO value of at least 20% by weight (polyisocyanate a), and b) 20-0% by weight of another polyisocyanate (polyisocyanate b), and wherein th e isocyanate-reactive composition consists of a) 80-100% by weight of a polyether polyol having an average nominal functionality of 3-8, an average equivalent weight of 200-2000, an average molecular weight of 600-8000, an oxyethylene (EO) content of 50-100 % and preferably of 75-100 % by weight an d a primary hydroxyl content of 70-100 % calculated on the number of primary a nd secondary hydroxyl groups in the polyol, b) an isocyanate-reactive chain extender and/or crosslinker in an amount such that the hard block ratio is 0.60 or more and preferably at least 0.65 and c) 20-0 % by weight of one or more other isocyanate-reactive compounds excluding water, the amount of poly ol a) and isocyanate-reactive compound c) being calculated on the total amount of this polyol a) and compound c).
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