Aqueous polyurethane composition for low gloss coatings

1. An aqueous coating composition having a 60° gloss of ≦30 upon drying comprising a self-crosslinkable polyurethane having an average particle size in the range of from 500 nm to 5000 nm 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) 5 to 25 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 anyone 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 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%.

7. A coating obtained from an aqueous coating composition according to claim 1 .

8. A coated substrate having a coating comprising an aqueous coating composition according to claim 1 .

9. 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.

10. 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.

11. An aqueous coating composition according to claim 1 additionally comprising a reactive diluent.