Process for rigid polyurethane foams

Abstract

Process for the preparation of open celled rigid polyurethane or urethane-modified polyisocyanurate foams by reaction of a polyfunctional isocyanate-reactive composition with a polyisocyanate composition comprising a prepolymer of NCO-value 21-30% based on a high molecular weight oxyethylene-containing polyol.

1 . Process for the preparation of an open-celled (semi-)rigid polyurethane or urethane-modified polyisocyanurate foam by reaction of a polyisocyanate composition with a polyfunctional isocyanate-reactive composition under foam-forming conditions, characterised in that the polyisocyanate composition has a free NCO-value of 21 to 30% by weight and comprises the reaction product of a stoichiometric excess of an organic polyisocyanate and an isocyanate-reactive material comprising a polyether polyol having a number average molecular weight between 1000 and 10000 and an average nominal hydroxyl functionality of from 2 to 6 and containing from 10 to 50% by weight of oxyethylene units.  
     
     
         2 . Process according to  claim 1  wherein the free NCO-value of the polyisocyanate composition is between 23 and 29 wt %.  
     
     
         3 . Process according to  claim 2  wherein the free NCO-value of the polyisocyanate composition is between 24 and 26 wt %.  
     
     
         4 . Process according to any one of the preceding claims wherein the polyether polyol has a number average molecular weight between 1000 and 6000.  
     
     
         5 . Process according to any one of the preceding claims wherein the polyether polyol has an average nominal hydroxyl functionality of from 2 to 4.  
     
     
         6 . Process according to any one of the preceding claims wherein the polyether polyol has an oxyethylene content of between 15 and 35% by weight.  
     
     
         7 . Process according to any one of the preceding claims wherein the polyether polyol is a poly(oxyethylene-oxypropylene) polyol.  
     
     
         8 . Process according to any one of the preceding claims wherein at least 50% of the oxyethylene groups are present at the end of the polyether polyol.  
     
     
         9 . Process according to any one of the preceding claims wherein the isocyanate-reactive material in the reaction product is used in an amount from 2 to 25% by weight based on the reaction product.  
     
     
         10 . Process according to any one of the preceding claims wherein the organic polyisocyanate is polymethylene polyphenylene polyisocyanate.  
     
     
         11 . Process according to any one of the preceding claims carried out in the presence of an isocyanate-reactive cyclic compound corresponding to the formula :  
       
         
           
           
               
               
           
         
       
       wherein Y is O or NR 1  wherein each R 1  independently is a lower alkyl radical of C 1 -C 6  or a lower alkyl radical substituted with an isocyanate-reactive group; each R independently is hydrogen, a lower alkyl radical of C 1 -C 6  or (CH 2 ) m —X wherein X is an isocyanate-reactive group which is OH or NH 2  and m is 0, 1 or 2; 
 and n is 1 or 2; with the proviso that at least one of R 1  or R is or comprises an isocyanate-reactive group.  
 
     
     
         12 . Process according to  claim 11  wherein the isocyanate-reactive cyclic compound corresponds to the formula (II) or (III):  
       
         
           
           
               
               
           
         
       
       
         
           
           
               
               
           
         
       
     
     
         13 . (Semi-)rigid open-celled polyurethane or urethane-modified polyisocyanurate foam obtainable by a process as defined in any one of  claims 1  to  12 .  
     
     
         14 . Evacuated insulation panel comprising a filler material and vessel formed of a gastight film enveloping said filler, characterised in that said filler material comprises a (semi-)rigid open-celled polyurethane or urethane-modified polyisocyanurate foam as defined in  claim 13 .  
     
     
         15 . Polyisocyanate composition having a free NCO-value of 21 to 30% by weight comprising the reaction product of a stoichiometric excess of an organic polyisocyanate and an isocyanate-reactive material comprising a polyether polyol having a number average molecular weight between 1000 and 10000 and an average nominal hydroxyl functionality of from 2 to 6 and containing from 10 to 50% by weight of oxyethylene units.