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  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 .