| 摘要 |
The prodn. of thermoplastic polyurethanes (TPU) comprises reacting: (a) opt. modified polyisocyanates with; (b) oligomeric polyhydroxy and/or polyamino cpd(s). with a mean mol. wt. of 400-10,000, opt. in the presence of; (c) chain extenders with a mol. wt. below 400 contg. at least two Zerewitinoff-reactive H atoms; (d) catalysts; (e) less than difunctional cpds. (w.r.t. isocyanates) and/or less than difunctional isocyanates; and (f) other additives etc., in a synchronous twin-screw extruder with a length/dia. (L/D) ratio of 20-60, followed by extrusion and moulding. The reaction mixt. is passed in succession through: (i) a first extruder zone (Z1) fitted with single-thread screw elements in a section starting at 0-3% and ending at least at 8-30% of the total screw length L; (ii) a low-shear mixing zone (Z2) contg. twin-thread screw and/or mixer elements in a zone between 8% and 45% of L, with a total length within this zone equal to 5-25% of L; (iii) a retention zone with a lower shearing action (Z3), in a zone between 20% and 50% of L, with a total length within this zone of 0.2-10% L; and (iv) a high-viscosity polymerisation zone (Z4) with twin-thread screw elements, in a zone between 30% and 100% of L, and then extruder. The process conditions are such that the value E = (M x n x Dg<2>)/V = more than 750; M = the total torque on both extruder screws (Nm); n = screw speed (r.p.m.); Dg = min. internal dia. of extruder housing (cm); V = free reactor vol. between the extruder housing and the screws and any other elements than the edge of the shaft (cm<3>). |
