| 摘要 |
1487564 Polyurethanes in finely divided form USM CORP 18 Sept 1974 [20 Sept 1973] 40759/74 Heading C3R Polyurethanes in finely divided form are prepared by reacting an organic polyisocyanate with an organic compound containing at least two active hydrogen-containing groups in an inert organic liquid reaction medium in which at least one of the reactants and the polyurethane product are insoluble and in the presence of a catalyst for the polyurethaneforming reaction, in which process the reactants are continuously fed to one or more mixing zones in which they are dispersed with vigorous agitation in the inert liquid, portions of the dispersion are continuously discharged therefrom to a further mixing zone wherein they reside for thickening by at least partial reaction of the reactants in the discharged portion to form a polyurethane, reaction of the reactants in the discharged portion is continued under conditions which retard settling of the dispersed material substantially to complete the reaction to form finely divided particles of the polyurethane and the polyurethane particles are separated from the inert liquid. The reaction is preferably carried out in a multi-zone mixer pulsator in which portions of the dispersion discharged from a first mixing zone are continuously introduced into a body of mixed components in at least one successive mixing zone and circulated for repeated agitation mixing, and portions of the dispersion in each successive zone are discharged continuously. A surfactant, which is preferably a vinyl pyrrolidone copolymer, may be employed to aid dispersion. In a typical Example, (1) an emulsion of a polytetramethylene ether glycol and 1,4 - butane diol in a liquid paraffinic hydrocarbon mixture is formed in the first zone of a mixer pulsator, portions of the emulsion are passed into a second zone into which 4,41- diphenylmethane diisocyanate is passed, the materials of the second zone are passed to a third zone where limited reaction takes place and material then passes to a fourth zone to form dispersed fine particles of polyurethane in a continuous phase of the liquid hydrocarbon. The particles may then be separated from the supernatant liquid.
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