Aqueous polymer dispersion, preparation and use thereof

Abstract

The present invention relates to an aqueous polymer dispersion comprising a copolymer of anhydride monomer units and vinyl monomer units, which copolymer has been subjected to an imidization reaction. The present invention further relates to a method for the production and use of such a dispersion.

1 . An aqueous polymer dispersion comprising a copolymer of anhydride monomer units and vinyl monomer units, which copolymer has been subjected to an imidization reaction, characterized in that at least 90 mole % of the anhydride monomer units of the copolymer are imidized.  
     
     
         2 . An aqueous dispersion as claimed in  claim 1 , characterized in that the anhydride monomer content of the copolymer ranges between 5-50 mole % and the vinyl monomer content of the copolymer ranges between 95-50 mole %.  
     
     
         3 . An aqueous dispersion as claimed in  claim 1 , characterized in that the copolymer has a molecular weight ranging between 1000-500000 g/mole.  
     
     
         4 . An aqueous dispersion as claimed  claim 1 , characterized in that the copolymer is a copolymer composition comprising a plurality of copolymers having varying molecular weights.  
     
     
         5 . An aqueous dispersion as claimed in  claim 1 , characterized in that the dispersion has a solid content of more than 20 wt. %.  
     
     
         6 . An aqueous dispersion as claimed in  claim 1 , characterized in that the polymer dispersion comprises discrete particles having a particle size between approximately 30-400 nm.  
     
     
         7 . An aqueous dispersion as claimed in  claim 1 , characterized in that the copolymer contains maleic anhydride monomer units and styrene monomer units.  
     
     
         8 . A method for the production of an aqueous polymer dispersion comprising the steps of 
 1) reacting a starting copolymer of anhydride monomer units and vinyl monomer units in an aqueous solution of NH 3  or an amine RNH 2 ,    2) subjecting the thus obtained mixture to an imidization reaction,    characterized in that the imidization reaction is carried out under reaction conditions which are selected so that at least 90 mole % of the anhydride monomer units have been imidized.    
     
     
         9 . A method as claimed in  claim 8 , characterized in that the imidization reaction is continued until a degree of imidization of the copolymer of at least 95 mole % is obtained.  
     
     
         10 . A method as claimed in  claim 8 , characterized in that the imidization reaction is carried out in the presence of an alkali salt of an acid functional polymer containing acid functional monomer units and vinyl aromatic monomer units.  
     
     
         11 . A method as claimed in  claim 8 , characterized in that the copolymer has a molecular weight ranging between 1000-500000 g/mole.  
     
     
         12 . A method as claimed in  claim 8 , characterized in that NH 3  or RNH 2  is added in such an amount that the ratio of NH 3  or amine:anhydride monomer in the starting copolymer is between 0.5-10:1.  
     
     
         13 . A method as claimed in  claim 8 , characterized in that the molar ratio between the amine or NH 3  and the anhydride monomer in the copolymer ranges between 1.2-0.8:1.  
     
     
         14 . A method as claimed in  claim 8 , characterized in that in the course of the imidization reaction, the reaction mixture is stirred so as to minimize adhesion of the reaction mixture to the reactor wall.  
     
     
         15 . A method as claimed in  claim 8 , characterized in that the imidization reaction is carried out at a temperature above 100° C.  
     
     
         16 . An aqueous coating composition for coating a product to be imprinted, characterized in that the coating composition contains a polymer dispersion as claimed in  claim 1 .  
     
     
         17 . An aqueous coating composition according to  claim 16 , further containing binders, conventional pigments and, optionally, additives.  
     
     
         18 - 19 . (canceled)  
     
     
         20 . A method of coating a surface to be imprinted comprising applying to said surface a polymer dispersion according to  claim 1 .  
     
     
         21 . A method according to  claim 20 , characterized in that the surface is paper, paperboard, cardboard, organic film e.g. polyethylene film, metal or textile.