Aqueous polyurethane compositions for low gloss coatings

Abstract

An aqueous coating composition having a 60° gloss of ≦40 upon drying comprising a self-crosslinkable polyurethane obtained by the reaction of: (A) an isocyanate-terminated pre-polymer formed from components which comprise (i) 5 to 65 wt % of at least one organic polyisocyanate; (ii) 0.8 to 4 wt % of at least one polyol containing ionic or potentially ionic water-dispersing groups, having two or more isocyanate-reactive groups and having a molecular weight in the range of from 100 up to 500 g/mol; (iii) 0 to 30 wt % of at least one polyol containing water-dispersing groups, having two or more isocyanate-reactive groups and having a molecular weight in the range of from 500 to 6000 g/mol; (iv) 10 to 80 wt % of at least one polyol containing crosslinkable groups, having two or more isocyanate-reactive groups and having a molecular weight in the range of from 150 to 6000 g/mol; (v) 10 to 70 wt % of at least one polyol not comprised by (iii) or (iv) having two or more isocyanate-reactive groups and having a molecular weight in the range of from 500 to 6000 g/mol; (vi) 0 to 50 wt % of at least one component not comprised by (i), (ii), (iii), (iv) or (v); where (i), (ii), (iii), (iv), (v) and (vi) add up to 100 wt %; and where the NCO:OH ratio is in the range of from 1.1:1.0 to 10.0:1.0; and (B) at least one active-hydrogen chain extending compound.

1 . An aqueous coating composition having a 60° gloss of ≦40 upon drying comprising a self-crosslinkable polyurethane obtained by the reaction of:
 (A) an isocyanate-terminated pre-polymer formed from components which comprise
 (i) 5 to 65 wt % of at least one organic polyisocyanate; 
 (ii) 0.8 to 4 wt % of at least one polyol containing ionic or potentially ionic water-dispersing groups, having two or more isocyanate-reactive groups and having an average molecular weight in the range of from 100 up to 500 g/mol; 
 (iii) 0 to 30 wt % of at least one polyol containing water-dispersing groups, having two or more isocyanate-reactive groups and having an average molecular weight in the range of from 500 to 6000 g/mol; 
 (iv) 10 to 80 wt % of at least one polyol containing crosslinkable groups, having two or more isocyanate-reactive groups and having an average molecular weight in the range of from 150 to 6000 g/mol; 
 (v) 10 to 70 wt % of at least one polyol not comprised by (iii) or (iv) having two or more isocyanate-reactive groups and having an average molecular weight in the range of from 500 to 6000 g/mol; 
 (vi) 0 to 50 wt % of at least one component not comprised by (i), (ii), (iii), (iv) or (v); where (i), (ii), (iii), (iv), (v) and (vi) add up to 100 wt %; and 
 where the NCO:OH ratio is in the range of from 1.1:1.0 to 10.0:1.0; and 
   (B) at least one active-hydrogen chain extending compound.   
   
   
       2 . An aqueous coating composition according to  claim 1  having a 85° gloss of ≦60. 
   
   
       3 . An aqueous coating composition according to any one of the preceding claims containing <5% by weight of flattening agent by weight of the self-crosslinkable polyurethane. 
   
   
       4 . An aqueous coating composition according to  claim 1  additionally comprising component (ia) 0 to 20 wt % of at least one organic polyisocyanate with an isocyanate functionality ≧2.2, where (i), (ii), (iii), (iv), (v), (vi)+(ia) add up to 100 wt %. 
   
   
       5 . An aqueous coating composition according to  claim 1  wherein component (vi) comprises a polysiloxane polyol. 
   
   
       6 . An aqueous coating composition according to  claim 1  wherein the self-crosslinkable polyurethane has an average particle size in the range of from 500 nm to 5000 nm 
   
   
       7 . An aqueous coating composition according to  claim 1  additionally comprising a reactive diluent. 
   
   
       8 . An aqueous coating composition comprising:
 I) 40 to 80 wt % of water,   II) 0 to 30 wt % of co-solvent;   III) 20 to 60 wt % of the self-crosslinkable polyurethane according to  claim 1 ;   IV) 0 to 10 wt % of hydrophobe modified ethylene oxide urethane;   V) 0 to 16 wt % of surfactants;   VI) 0 to 10 wt % of thickeners; and   VII) 0 to 3 wt % of alkyd drying agent, accelerator and/or activator;   where I), II), IiI), IV), V), VI) and VII) add up to 100%.   
   
   
       9 . A coating obtained from an aqueous coating composition according to  claim 1 . 
   
   
       10 . A coated substrate having a coating comprising an aqueous coating composition according to  claim 1 . 
   
   
       11 . A method of coating a substrate using an aqueous coating composition according to  claim 1 , comprising (a) application of the aqueous coating composition to a substrate and (b) removal of the water and any co-solvent. 
   
   
       12 . A process for preparing an aqueous coating composition according to  claim 1  comprising the following steps:
 a) reaction of components (i) to (vi) to form an isocyanate-terminated prepolymer (A);   b) forming an aqueous dispersion of the isocyanate-terminated prepolymer (A) in water;   c) optionally neutralising the isocyanate-terminated prepolymer (A) after and/or during step a) and/or step b);   d) chain extension of the isocyanate-terminated prepolymer (A) by reaction with the active-hydrogen chain extending compound (B); and   e) optionally adding crosslinker.