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An aqueous dispersion of polyurethane-addition polymer hybrid particles, where the isocyanates used to make the polyurethane polymer portion of the particles comprise a mixture of aromatic polyisocyanate and aliphatic polyisocyanate wherein the aromatic isocyanate is free of sterically hindered isoc

An aqueous dispersion of polyurethane-addition polymer hybrid particles, where the isocyanates used to make the polyurethane polymer portion of the particles comprise a mixture of aromatic polyisocyanate and aliphatic polyisocyanate wherein the aromatic isocyanate is free of sterically hindered isocyanate moieties. The dispersions are suitable for use in coatings, including varnishes, paints, inks and adhesives.

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The invention claimed is: 1. An aqueous dispersion of polyurethane-addition polymer, comprising hybrid particles having a weight average mean diameter of less than 1000 nm comprised of: i) polyurethane polymer; ii) addition copolymer of ethylenically unsaturated copolymerisable monomers, where the

The invention claimed is: 1. An aqueous dispersion of polyurethane-addition polymer, comprising hybrid particles having a weight average mean diameter of less than 1000 nm comprised of: i) polyurethane polymer; ii) addition copolymer of ethylenically unsaturated copolymerisable monomers, where the polyurethane polymer of i) is the reaction product of: a) aromatic polyisocyanate that is essentially free of sterically hindered isocyanate moieties; b) aliphatic polyisocyanate, wherein the isocyanate functionality of the aromatic polyisocyanate is from 1.8 to 2.3 and the isocyanate functionality of the aliphatic polyisocyanate is up to 4; c) compound containing two hydroxyl moieties reactive with the isocyanate moieties of a) and b); d) compound containing at least one dispersing moiety and at least one moiety reactive with the isocyanate moieties of a) and b), wherein the ratio of the total number of isocyanate moieties from the aromatic polyisocyanate to the total number of the isocyanate reactive moieties of c) and d) is from 0.50 to 1.45; and e) chain extender compound. 2. An aqueous dispersion according to claim 1, characterized in that the isocyanate functionality of the aromatic polyisocyanate is from 1.9 to 2.1 and the isocyanate functionality of the aliphatic polyisocyanate is from 1.7 to 3. 3. An aqueous dispersion according to claim 1 characterised in that the hybrid polymer particles have a weight average mean diameter selected from those from 20 to 650 nm, or from 20 to 200 nm., or from 20 to 90 nm. as this produces transparent dispersions. 4. An aqueous dispersion according to claim 1 characterised in that the hybrid polymer particles have a weight average mean diameter in the range from 20 to 90 nm. to produce transparent dispersions. 5. An aqueous dispersion according to claim 1 characterised in that the hybrid polymer particles are of the core-shell type. 6. An aqueous coating composition comprising a dispersion according to claim 1. 7. An aqueous coating composition according to claim 5 characterised in that the composition also contains ingredients selected from the group comprising pigments, fillers, waxes, extenders, rheological modifiers, dispersants, anti-foams, tackifiers, plasticisers, crosslinking agents, flow aids, biocides, and combinations of any two or more of these. 8. A method of applying an aqueous coating composition to a substrate by brush, roller, blade or spray equipment characterized in that the composition is according to claim 5. 9. An aqueous coating composition according to claim 5 characterised in that the coating is selected from paints suitable for painting wood, floors, ceilings, metal, beverage and food containers; plastics, masonry, walls as a primer, undercoat, topcoat, lacquer, varnish, woodstain, or ink. 10. Process for making the aqueous coating composition of claim 5, comprising combining with the aqueous dispersion of Polyurethane-addition polymer hybrid particles at least one ingredient selected from pigments, fillers, waxes, extenders, rheological modifiers, dispersants, anti-foams, tackifiers, plasticisers, crosslinking agents, flow aids, biocides, and combinations of any two or more of these. 11. A process of making the aqueous dispersion of polyurethane-addition polymer hybrid particles of claim 1, comprising the steps of: a) reacting at an elevated temperature the compound containing two hydroxyl moieties with a molar excess of isocyanate moieties provided by a mixture of the aromatic polyisocyanate and aliphatic polyisocyanate, where the aromatic polyisocyanate is essentially free of sterically hindered isocyanate moieties; b) reacting some of the excess isocyanate moieties of the reaction product of a) with a compound containing at least one ionisable group and at least one moiety reactive with the isocyanate moieties to form a dispersible ionisable urethane prepolymer; c) forming a solution of the ionisable polyurethane prepolymer in the ethylenically unsaturated monomers and dispersing the solution in water in the presence of a neutralizing agent to form an emulsion; d) causing the molecular weight of the prepolymer to increase by reacting it with the chain extender compound; and e) causing the ethylenically unsaturated monomers to copolymerize. 12. An aqueous dispersion of polyurethane-addition polymer, comprising hybrid particles having a weight average mean diameter of less than 1000 nm and comprising: i) polyurethane polymer; ii) addition copolymer of ethylenically unsaturated copolymerisable monomers, where the polyurethane polymer of i) is the reaction product of: a) aromatic polyisocyanate that is essentially free of sterically hindered isocyanate moieties; b) aliphatic polyisocyanate, whereby the ratio on a molar basis of the aromatic polyisocyanate to the aliphatic polyisocyanate ranges from 10:90 to 90:10; c) compound containing two hydroxyl moieties reactive with the isocyanate moieties of a) and b); d) compound containing at least one dispersing moiety and at least one moiety reactive with the isocyanate moieties of a) and b), wherein the ratio of the total number of isocyanate moieties from the aromatic polyisocyanate to the total number of the isocyanate reactive moieties of c) and d) is from 0.50 to 1.45; and e) chain extender compound. 13. An aqueous dispersion according to claim 12 characterised in that the dispersing moiety is non-ionisable. 14. An aqueous dispersion according to claim 12 characterised in that the dispersing moiety is ionisable. 15. An aqueous dispersion according to claim 12, characterized in that the ratio of the total number of isocyanate moieties from the aromatic polyisocyanate to the total number of the isocyanate reactive moieties of c) and c) is from 0.5 to 1.3. 16. An aqueous dispersion according to claim 12, characterized in that the ratio of the total number of isocyanate moieties from the aromatic polyisocyanate to the total number of the isocyanate reactive moieties of c) and d) is from 0.8 to 1.25. 17. An aqueous dispersion according to claim 12, characterized in that the aromatic polyisocyanate has only a hydrogen atom on each of the aromatic ring carbons adjacent the aromatic ring carbons carrying an isocyanate moiety; and/or a fused aromatic ring adjacent to the aromatic ring carbons carrying an isocyanate moiety. 18. An aqueous dispersion according to claim 12 characterised in that the aromatic polyisocyanate is selected from the group comprising 4,4' methane diphenyl diisocyanate, para-phenylene diisocyanate, carbodiimide modified methane diphenyl diisocyanate and 1,5 naphthalene diisocyanate. 19. An aqueous dispersion according to claim 12, characterized in that the aromatic polyisocyanate is 4,4' methane diphenyl diisocyanate. 20. An aqueous dispersion according to claim 12, characterized in that the aliphatic polyisocyanate is 4,4' dicyclohexyl methane diisocyanate. 21. An aqueous dispersion according to claim 12, characterized in that the addition copolymer is derived from the esters of acrylic acid, methacrylic acid and optionally styrene and/or its derivatives. 22. An aqueous dispersion according to claim 12, characterized in that the ratio of polyurethane polymer to addition polymer is from 30:70 to 70:30. 23. An aqueous dispersion according to claim 12 characterised in that the hybrid polymer particles have a weight average mean diameter selected from those from 20 to 650 nm, or from 20 to 200 nm. or from 20 to 90 nm. as this produces transparent dispersions. 24. An aqueous dispersion according to claim 12 characterised in that the hybrid polymer particles have a weight average mean diameter in the range from 20 to 90 nm. to produce transparent dispersions. 25. An aqueous dispersion according to claim 12 characterised in that the hybrid polymer particles are of the core-shell type. 26. An aqueous coating composition comprising a dispersion according to claim 12.