Waterborne coating composition

An aqueous vinyl polymer dispersion PD comprising:

• 1) an aqueous dispersion or solution of a vinyl oligomer OL1 obtainable by free radical emulsion copolymerization of a monomer mixture comprising:
• a) from 5 to 20 wt % of acid functional ethylenically unsaturated monomers M1 or precursors thereof;
• b) from 5 to 90 wt % of non-ionic ethylenically unsaturated monomers M2 other than M1;
• c) from 0.5 to 10 wt % of ethylenically unsaturated monomers M3 with a functional group for cross-linking after film-formation;
• d) from 0.5 to 10 wt % of at least one chain transfer agent CTA;
• where the sum of the weight percentages of monomers M1, M2, M3 and chain transfer agent CTA equals to 100 wt %;
• 2) an aqueous dispersion of vinyl oligomer OL2 obtainable by free radical emulsion copolymerization of:
• a) from 0 to 5 wt % of acid functional ethylenically unsaturated monomers M1′ or precursors thereof;
• b) from 5 to 99.5 wt % of non-ionic ethylenically unsaturated monomers M2′ other than M1′;
• c) from 0 to 5 wt % of ethylenically unsaturated monomers M3′ with a functional group for cross-linking after film-formation;
• d) from 0 to 5 wt % of adhesion promoting ethylenically unsaturated monomers M4′;
• e) from 0 to 3 wt % of a polyethylenically unsaturated monomer M5′;
• f) from 0.5 to 10 wt % of at least one chain transfer agent CTA′;
• where the sum of the weight percentages of monomers M1′, M2′, M3′, M4′, M5′ and chain transfer agent CTA′ equals to 100 wt %;
• and
• 3) a vinyl polymer P under the form of an aqueous dispersion comprising:
• a) from 0 to 5 wt % of acid functional ethylenically unsaturated monomers M1″ or precursors thereof;
• b) from 5 to 99.5 wt % of non-ionic ethylenically unsaturated monomers M2″ other than M1″;
• c) from 0 to 5 wt % of ethylenically unsaturated monomers M3″ with a functional group for cross-linking after film-formation;
• d) from 0 to 5 wt % of adhesion promoting ethylenically unsaturated monomers M4″;
• e) from 0 to 3 wt % of a polyethylenically unsaturated monomer M5″;
• f) from 0 to 1 wt % of at least one chain transfer agent CTA″;
• where the sum of the weight percentages of monomers M1″, M2″, M3″, M4″, M5″ and chain transfer agent CTA″ equals to 100 wt %,
• wherein the weight ratio of vinyl oligomers OL1 and OL2 to vinyl polymer P ranges from 10:45:45 to 90:5:5, and
• wherein the aqueous vinyl polymer dispersion PD is made by a process comprising at least the following subsequent steps 1) to 3):
• 1) making vinyl oligomer OL1 with acid functionality by polymerizing the monomers for vinyl oligomer OL1, after which oligomer OL1 is partially or completely dissolved by the addition of a base,
• and
• 2) polymerizing the monomers for vinyl oligomer OL2 in the presence of the neutralized vinyl oligomer OL1 and
• 3) polymerizing the monomers for vinyl polymer P in the presence of both the neutralized vinyl oligomer OL1 and the vinyl oligomer OL2 previously formed,
• or
• 2) polymerizing the monomers for vinyl polymer P in the presence of the neutralized vinyl oligomer OL1 and
• 3) polymerizing the monomers for vinyl oligomer OL2 in the presence of both the neutralized vinyl oligomer OL1 and the vinyl polymer P previously formed.