Aqueous PU dispersions with improved adhesion

Abstract

A process for preparing polyester-polyurethane resin dispersions that includes: A) reacting one or more polyol components i) having an average molecular weight of at least 300, at least one of the components being a polyester polyol and the fraction of polyester polyol based on aromatic polycarboxylic acids being more than 50% by weight with a polyisocyanate to form a prepolymer, B) dissolving the prepolymer in an organic solvent; C) reacting the prepolymer with aliphatic polyamines having a molecular weight of 60 to 300 or hydrazine and a hydrophilicized aliphatic diamine, D) precipitating the product from C) by adding water to form a dispersion, and E) removing the organic solvent. The resulting polyester-polyurethane resin dispersions can be used in coating compositions and in coating systems that include a substrate and one or more coating films, at least one of which includes the polyester-polyurethane resin dispersion.

1 . A process for preparing polyester-polyurethane resin dispersions, comprising 
 A) reacting one or more polyol components i) having an average molecular weight of at least 300 daltons, at least one of the components being a polyester polyol and the fraction of polyester polyol based on aromatic polycarboxylic acids being more than 60% by weight, optionally one or more polyol components having an average molecular weight of 62 to 299 daltons, and optionally a compound which is monofunctional for the purposes of the isocyanate polyaddition reaction and has an ethylene oxide content of at least 50% by weight and a molecular weight of at least 400 daltons with a polyisocyanate to form a prepolymer,    B) dissolving the prepolymer in an organic solvent;    C) reacting the prepolymer with one or more aliphatic polyamines having a molecular weight of 60 to 300 daltons or hydrazine and a hydrophilicized aliphatic diamine,    D) precipitating the product from C) by adding water to form a dispersion, and    E) removing the organic solvent.    
     
     
         2 . The process according to  claim 1 , wherein the fraction of polyester polyol based on aromatic polycarboxylic acids is more than 60% by weight.  
     
     
         3 . The process according to  claim 1 , wherein the fraction of aromatic carboxylic acid groups, relative to all of the carboxylic acid groups used to prepare the polyester component, in the polyol component i) is at least 70 mol %.  
     
     
         4 . The process according to  claim 1 , wherein the fraction of aromatic carboxylic acid groups, relative to all of the carboxylic acid groups used to prepare the polyester component, in the polyol component i) is at least 80 mol %.  
     
     
         5 . A polyester-polyurethane resin dispersions obtained according to the process of  claim 1 .  
     
     
         6 . A coating compositions comprising 15 to 45 parts by weight of an aqueous polyester-polyurethane resin dispersion according to  claim 6 ,  15  to  45  parts by weight of a hydroxy-functional, aqueous or water-dilutable binder, 0 to 60 parts by weight of an inorganic filler and/or matting agent, 1 to 60 parts by weight of a polyisocyanate, 0.1 to 30 parts by weight of pigments and 1 to 15 parts by weight of customary coatings auxiliaries, the sum of the components making 100.  
     
     
         7 . A coating system comprising a substrate and one or more coating films, wherein at least one of the coating films comprises the polyester-polyurethane resin dispersion according to  claim 5.