Reducing cold stress whitening

Abstract

Undesirable changes in shade brought about by low temperatures (Cold Stress Whitening) in impact-modified thermoplastic molding compositions F which comprise at least one elastomeric graft polymer A and at least one thermoplastic polymer B are reduced by adding from 10 to 200 ppm, based on the molding compositions F, of at least one polyorganosiloxane S to the impact-modified thermoplastic molding composition F.

We claim:  
     
         1 . A process for reducing undesirable changes in shade brought about by low temperatures (Cold Stress Whitening) in impact-modified thermoplastic molding compositions F which comprise at least one elastomeric graft polymer A and at least one thermoplastic polymer B, in which from 10 to 200 ppm, based on the molding compositions F, of at least one polyorganosiloxane S are added to the impact-modified thermoplastic molding composition F.  
     
     
         2 . A process as claimed in  claim 1 , wherein the polyorganosiloxane S is added to the impact-modified thermoplastic molding composition F before the molding composition F is further processed in mixing apparatuses or in apparatuses for producing moldings.  
     
     
         3 . A process as claimed in  claim 1  or  2 , wherein the elastomeric graft polymer A is prepared in emulsion or in suspension, in which process a rubber latex is produced, and wherein a polyorganosiloxane S is added to the reaction mixture at the latest prior to the coagulation of the rubber latex.  
     
     
         4 . A process as claimed in any of  claims 1  to  3 , wherein the amount of the polyorganosiloxane S added is from 10 to 190 ppm, based on the molding composition F.  
     
     
         5 . A process as claimed in any of  claims 1  to  4 , wherein the polyorganosiloxane S used comprises a polydimethylsiloxane with a viscosity of from 10·10 −6  to 100 000·10 −6  m 2 /s.  
     
     
         6 . A process as claimed in any of  claims 1  to  5 , wherein the rubber present in the elastomeric graft polymer A comprises a diene rubber, alkyl acrylate rubber or EPDM rubber.  
     
     
         7 . A process as claimed in any of  claims 1  to  6 , wherein, are present in the thermoplastic polymer B styrene and/or a-methylstyrene, and acrylonitrile.  
     
     
         8 . A process as claimed in any of  claims 1  to  7 , wherein the impact-modified molding composition F is an ABS molding composition.  
     
     
         9 . The use of polyorganosiloxanes S for the reduction of undesirable shade changes brought about by low temperatures (Cold Stress Whitening) in impact-modified thermoplastic molding compositions F which comprise at least one elastomeric graft polymer A and at least one thermoplastic polymer B.  
     
     
         10 . The use of polyorganosiloxanes S as claimed in  claim 9  in ABS molding compositions.