POLYISOCYANATE MIXTURES WHICH ARE LIQUID AT GREATER THAN 5° C
The present invention relates to polyisocyanate mixtures which are reaction products of 4,4'-diphenylmethane diisocyanate as the isocyanate component, are liquid at greater than 5.degree.C and have an NCO content of 14.5 to 24% by weight and an allophanate group content (calculated as C2HN2O3,...
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Zusammenfassung: | The present invention relates to polyisocyanate mixtures which are reaction products of 4,4'-diphenylmethane diisocyanate as the isocyanate component, are liquid at greater than 5.degree.C and have an NCO content of 14.5 to 24% by weight and an allophanate group content (calculated as C2HN2O3, molecular weight = 101) of 7.7 to 14.5% by weight; a process for the production of these polyisocyanate mixtures by reacting 4,4'-diphenylmethane diisocyanate as the exclusive isocyanate component with one or more monohydric alcohols having 4 to 16 carbon atoms at an NCO/OH equivalent ratio of 5:1 to 8.5:1 and at a temperature of up to 160.degree.C to form urethane groups and during or subsequent to urethane formation, converting the urethane groups to allophanate groups in the presence of a catalyst which promotes allophanate formation; and the use of these polyisocyanate mixtures as the polyisocyanate component in two-component polyurethane coating compositions. |
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