Radiation curable aqueous composition for low gloss coatings

Abstract

A radiation curable aqueous coating composition having a 85° gloss of ≦60 upon drying comprising (A) 10 to 99 wt % of a polyurethane, (B) 1 to 90 wt % of a radiation curable component; (C) 0.1 to 10 wt % of an associative thickener; wherein at least 80 wt % of (A)+(B)+(C) has a particle size greater than 500 nm and wherein the C═C bond concentration of the composition is 0.2 to 5.0 mmol per g of (A)+(B)+(C).

1 . A radiation curable aqueous coating composition having a 85° gloss of ≦60 upon curing comprising:
 (A) 10 to 99 wt % of a polyurethane obtained by the reaction of components comprising:
 (i) 5 to 65 wt % of at least one organic polyisocyanate; 
 (ii) 0.1 to 6 wt % of at least one isocyanate-reactive component containing ionic or potentially ionic water-dispersing groups having a molecular weight in the range of from 100 up to 500 g/mol; 
 (iii) 0 to 30 wt % of at least one isocyanate-reactive component containing water-dispersing groups and having a molecular weight in the range of from 500 to 6000 g/mol; 
 (iv) 0 to 80 wt % of at least one isocyanate-reactive component containing radiation curable functional groups and having a molecular weight in the range of from 70 to 6000 g/mol; 
 (v) 0 to 50 wt % of at least one component not comprised by (i), (ii), (iii), (iv) or (vi); 
 (vi) 0 to 50 wt % of at least one active-hydrogen chain extending compound; 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 0.4:1.0 to 10.0:1.0; 
   (B) 1 to 90 wt % of a radiation curable component; and   (C) 0.1 to 10 wt % of an associative thickener;   wherein (A)+(B)+(C) add up to 100 wt %; and   wherein at least 80 wt % of the polyurethane (A)+(B)+(C) has a particle size greater than 500 nm; and wherein the C═C bond concentration of the composition is 0.2 to 5.0 mmol per g of (A)+(B)+(C).   
   
   
       2 . An aqueous coating composition according to  claim 1  containing <5% by weight of flattening agent by weight of the polyurethane (A). 
   
   
       3 . An aqueous coating composition according to  claim 1  wherein the aqueous coating composition is UV radiation curable. 
   
   
       4 . An aqueous coating composition according to  claim 1  wherein the 60° gloss of the aqueous coating composition upon curing is ≦40. 
   
   
       5 . An aqueous coating composition according to  claim 1  wherein at least 85 wt % of (A)+(B)+(C) has a particle size greater than 500 nm and less than 25000 nm. 
   
   
       6 . An aqueous coating composition according to  claim 1  wherein the mean particle size (D[0.1]) of (A)+(B)+(C) is greater than 500 nm and less than 90000 nm. 
   
   
       7 . An aqueous coating composition according to  claim 1  wherein polyurethane (A) comprises 0.5 to 3.0 wt % of neutralised component (ii). 
   
   
       8 . An aqueous coating composition according to  claim 1  wherein radiation curable component (B) is selected from the group consisting of epoxy (meth)acrylates; urethane (meth)acrylates; multi-functional (meth)acrylate monomers; UV-curable urethane dispersions, amine-(meth)acrylate adducts and mixtures thereof. 
   
   
       9 . An aqueous coating composition according to  claim 1  wherein the composition comprises 1 to 30 wt % of a low molecular weight radiation curable component (B1). 
   
   
       10 . An aqueous coating composition according to  claim 1  wherein the composition comprises 10 to 90 wt % of a low molecular weight radiation curable component (B2). 
   
   
       11 . An aqueous coating composition according to  claim 1  wherein the associative thickeners component (C) is selected from the group consisting of hydrophobic modified water soluble polymers, hydrophobically modified alkali soluble emulsions and mixtures thereof. 
   
   
       12 . An aqueous coating composition according to  claim 1  additionally comprising a vinyl polymer. 
   
   
       13 . An aqueous coating composition according to  claim 12  wherein the ratio of the vinyl polymer to polyurethane (A) is in the range of from 10:90 to 90:10. 
   
   
       14 . 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 polyurethane (A);   b) forming an aqueous dispersion of the polyurethane (A) in water;   c) optionally neutralising the polyurethane (A);   d) adding at least a radiation curable component (B);   e) adding at least an associative thickener;   f) optionally adding a radiation initiator;   g) optionally adding vinyl monomer;   where steps b), c), d), e), f) and g) may be in any order.   
   
   
       15 . A coating obtained from an aqueous coating composition according to  claim 1 .