Abstract: In order to prepare thermoplastic polyurethane elastomers(a) organic diisocyanate,(b) polyhydroxyl compounds with molecular weights of 500 to 8,000, and(c) chain extenders with molecular weights of 60 to 400 in the presence of(d) catalysts, and optionally(e) auxiliaries, and/or(f) additivesare reacted in two reaction stages at temperatures from 60.degree. C. to 250.degree. C. In the first reaction stage the components are continuously mixed, the reaction mixture is applied to a carrier, preferably a conveyor band of thermoplastic material, and is allowed to react at the reaction temperature until solidified. Subsequently, the solidified reaction mixture is melted in an extruder and the reaction is completed in the second reaction stage.

Abstract: A process for the manufacture of non-cellular and cellular polyurethane elastomers by(a) preparing a hydroxyl group-containing prepolymer by reacting a higher molecular weight polyhydroxyl compound and optionally a chain extender with an organic diisocyanate at a weight ratio of OH groups to NCO groups of 1.2:1 to 2:1,(b) dividing the prepolymer into two components A and B in a weight ratio of about 80:20 to 20:80,(c) reacting component A with 1,5-naphthylene diisocyanate (NDI) in a weight ratio of OH:NCO groups of about 1:2.5 to 1:12 to produce a terminal NCO group-containing NDI-polyurethane adduct,(d) mixing component B with chain extenders and/or cross-linking agents and/or water, and optionally auxiliaries and additives, and(e) reacting the NDI-polyurethane adduct (from step c) with the mixture from step d.

Abstract: A mixing apparatus for mixing components that interact chemically, preferably polyurethane-forming components, the apparatus including a control plunger disposed within a housing and movable along a mixing chamber between opposing inlet and return ports, the control plunger having along its wall surface return grooves for connecting the inlet ports to the return ports when the plunger is in a position blocking communication between the inlet ports and the mixing chamber wherein a wall surface portion of the control plunger which in the closing position of the plunger is disposed intermediate the return ports is provided with discrete recesses which mutually overlap in the direction of movement of the control plunger.

Abstract: Laminates for the production of relief plates for flexographic printing, by imagewise exposure and washing out with a developer solution have, on a base optionally provided with an elastomeric layer, a photo-crosslinkable layer containing a photoinitiator and consisting of a polyurethane elastomer which has been prepared in a special manner from an aliphatic saturated polyesterglycol, an aliphatic diisocyanate, but-1-ene-3,4-diol and, if desired, another diol and which has a Shore A hardness of 30 to 90.degree. in the photo-crosslinked state, the elastomer being optionally mixed with a photo-crosslinked monomer.