Process for producing a polyurethane foam and polyurethane foam obtainable therefrom

Abstract

A process for producing a polyurethane foam with bimodal cell size distribution, comprising the following steps: providing a mixture in a mixing head, where the mixture comprises: A) a component reactive towards isocyanates; B) a surfactant component; C) a blowing agent component selected from the group consisting of linear, branched or cyclic C 1 - to C 6 -alkanes, linear, branched or cyclic C 1 - to C6-fluoroalkanes, N 2 , O 2 , argon and/or CO 2 , where blowing agent component C) is present in the supercritical or near-critical state; D) a polyisocyanate component; discharging the mixture comprising components A), B), C), and D) from the mixing head where, during the discharge of the mixture, the pressure prevailing in the mixture is lowered to atmospheric pressure.

1 . A polyurethane foam obtained by the process comprising the following steps:
 providing a mixture in a mixing head, where the mixture comprises:
 A) a component reactive towards isocyanates; 
 B) a surfactant component; 
 C) a blowing agent component selected from the group consisting of linear, branched or cyclic C 1 - to C 6 -alkanes, linear, branched or cyclic C 1 - to C 6 -fluoroalkanes, N 2 , O 2 , argon and/or CO 2 ; 
 wherein the blowing agent component C) is present in the supercritical or near-critical state; and 
 D) a polyisocyanate component; 
   discharging the mixture comprising components A), B), C), and D) from the mixing head wherein, during the discharge of the mixture, the pressure prevailing in the mixture is lowered to atmospheric pressure.   
     
     
         2 . The polyurethane foam according to  claim 1 , present in the form of foam with an average pore diameter of from ≧10 nm to ≦10 000 nm. 
     
     
         3 . The polyurethane foam according to  claim 2  with bimodal cell size distribution, wherein one maximum of the cell size distribution is in the range from ≧10 nm to ≦500 nm and a further maximum of the cell size distribution is in the range from ≧1 μm to ≦500 μm. 
     
     
         4 . The polyurethane foam according to  claim 2  with a pore density of from ≧10 9  pores/cm 3  to ≦10 18  pores/cm 3 . 
     
     
         5 . The polyurethane foam according to  claim 2  with a thermal conductivity of from ≧6 mW/m K to ≦30 mW/m K.