Aqueous coating composition with soft touch upon drying
Aqueous coating compositions include dispersed polyurethane-vinyl polymer hybrid particles obtained by free-radical polymerization of at least one vinyl monomer in the presence of a polyurethane. The polyurethane and the vinyl polymer in the hybrid particles are present in a weight ratio of polyurethane to vinyl polymer ranging from 1:1 to 20:1, and the polyurethane is the reaction product of at least the following components: (a) from 5 to 40 wt. % of at least one organic difunctional isocyanate, (b) from 0.5 to 4 wt. % of an isocyanate-reactive compound containing ionic or potentially ionic water-dispersing groups having a molecular weight of from 100 to 500 g/mol, (c) from 40 to 80 wt. % of at least one diol having a molecular weight from 500 to 5000, (d) from 0 to 10 wt. % of at least one active-hydrogen chain extending compound with a functionality of at least 2 other than water, (e) from 0 to 10 wt. % of at least one diol having a molecular weight below 500 g/mol. The isocyanate and hydroxy groups on the components used are present in a respective mole ratio (NCO to OH) in the range of from 0.8:1 to 5:1.
1. An aqueous coating composition comprising dispersed polymer particles, wherein
(i) the dispersed polymer particles are polyurethane-vinyl polymer hybrid particles obtained by free-radical polymerization of at least one vinyl monomer in the presence of a polyurethane,
(ii) the polyurethane and the vinyl polymer in the hybrid particles are present in a weight ratio of polyurethane to vinyl polymer ranging from 2:1 to 16:1,
(iii) the polyurethane is obtained by the reaction of at least the following components:
(a) from 10 to 35 wt. % of at least one organic difunctional isocyanate,
(b) from 1 to 2.5 wt % of an isocyanate-reactive compound containing ionic or potentially ionic water-dispersing groups having a molecular weight of from 100 to 500 g/mol,
(c) from 45 to 75 wt. % of at least one diol having a molecular weight from 500 to 5000,
(d) from 0.5 to 10 wt. % of at least one active-hydrogen chain extending compound with a functionality of at least 2 other than water,
(e) from 0 to 10 wt. % of at least one diol having a molecular weight below 500 g/mol, wherein
the amounts of (a), (b), (c), (d) and (e) are given relative to the total amount of components used to prepare the polyurethane from which the building blocks from the polyurethane are emanated, and wherein
isocyanate (NCO) groups and hydroxy (OH) groups on the components used to prepare the polyurethane are present in a mole ratio of the NCO groups to the OH groups in the range of from 1.05:1 to 5:1, and wherein
(iv) the dispersed polymer particles have a mean particle size (D[0.5]]) greater than 1.2 micron, and
(v) the dispersed polymer particles have a mean particle size (D[0.9]) less than 10 micron.
2. The aqueous coating composition according to claim 1 , wherein the coating composition comprises:
(A) 75 to 99.7 wt. % of the dispersed polymer particles,
(B) 0.2 to 15 wt. % of a rheology additive, and
(C) 0.1 to 10 wt. % of a surfactant.
3. The aqueous coating composition according to claim 1 , wherein at least 30 wt. %, of the total amount of vinyl monomer(s) used to prepare the vinyl polymer is selected from the group consisting of methyl methacrylate, butyl acrylate, butyl methacrylate, acrylonitrile, styrene and mixtures of two or more of said monomers.
4. The aqueous coating composition according to claim 1 , wherein the diol (c) has a glass transition temperature Tg from −110° C. to +110° C.
5. The aqueous coating composition according to claim 1 , wherein the amount of active-hydrogen chain extending compound with a functionality of at least 2 (d) is from 1 to 3 wt. %, and wherein the mole ratio of the NCO groups to the OH groups is in the range of from 1.1:1 to 3.5:1.
6. The aqueous coating composition according to claim 1 , wherein the polyurethane of the polyurethane-vinyl polymer hybrid particles is crosslinked.
7. The aqueous coating composition according to claim 6 , wherein the crosslinked polyurethane is prepared by further adding at least one of the following crosslinkers (f), (g) and (d′):
(f) from 1 to 20 wt. % of at least one organic polyisocyanate with an average functionality of >2.3,
(g) from 1 to 10 wt. % of at least one polyol having a molecular weight of 500-5000 g/mol and an average functionality of at least 2.3,
(d′) at least one active-hydrogen chain extending compound with a functionality of 3 or higher in an amount of at least 50 wt. % of component (d), wherein
the amounts of (f), (g) and (d′) are given relative to the total amount of components (a), (b), (c), (d, including d′), (e), (f) and (g), used to prepare the polyurethane.
8. The aqueous coating composition according to claim 7 , wherein the total amount of (f), (g) and (d′) are together more than 3 wt. % relative to the total amount of components (a), (b), (c), (d, including d′), (e), (f) and (g), used to prepare the polyurethane and the total amount of (f), (g) and (d′) are preferably together at most 20 wt. %, relative to the total amount of components (a), (b), (c), (d, including d′), (e), (f) and (g), used to prepare the polyurethane.
9. The aqueous coating composition according to claim 7 , wherein the active-hydrogen chain extending compound with a functionality of 3 or higher (d′) is a polyamine with a functionality of 3.
10. The aqueous composition according to claim 7 , wherein (f) is selected from the group consisting of hexamethylene diisocyanate isocyanurate, hexamethylene diisocyanate biuret, isophorone diisocyanate isocyanurate and any mixture thereof.
11. The aqueous coating composition according to claim 6 , wherein the aqueous coating composition is a one-component (1K) composition.
12. The aqueous coating composition according to claim 1 , wherein the mean particle size (D[0.5]) of the dispersed polymer particles (A) is greater than 1.5 micron.
13. The aqueous coating composition according to claim 1 , wherein the mean particle size (D[0.9]) of the dispersed polymer particles (A) is less than 6 micron.
14. The aqueous coating composition according to claim 1 , wherein the total amount of the active-hydrogen chain extending compound is such that the molar ratio of active hydrogens in the active hydrogen chain extending compound to isocyanate groups in the polyurethane prepolymer is in the range 0.6:1 to 1.4:1.
15. The aqueous coating composition according to claim 14 , wherein the molar ratio of active hydrogens in the chain extender to isocyanate groups in the polyurethane prepolymer is in the range from 0.8 to 1.2.
16. The aqueous coating composition according to claim 1 , wherein the resulting coating composition is free of organic solvent.
17. The aqueous coating composition according to claim 1 , wherein the polyurethane and the vinyl polymer in the hybrid particles are present in a weight ratio of polyurethane to vinyl polymer ranging from 3:1 to 12:1.
18. The aqueous coating composition according to claim 1 , wherein the polyurethane and the vinyl polymer in the hybrid particles are present in a weight ratio of polyurethane to vinyl polymer ranging from 4:1 to 12:1.
19. The aqueous coating composition according to claim 1 , wherein the polyurethane and the vinyl polymer in the hybrid particles are present in a weight ratio of polyurethane to vinyl polymer ranging from 4:1 to 10:1.
20. The aqueous coating composition according to claim 1 , wherein at least 70 wt. % of the total amount of vinyl monomer(s) used to prepare the vinyl polymer is selected from the group consisting of methyl methacrylate, butyl acrylate, butyl methacrylate, acrylonitrile, styrene and mixtures of two or more of said monomers.
21. The aqueous coating composition according to claim 6 , wherein the polyol (g) has a glass transition temperature Tg from −110° C. to +110° C.
22. The aqueous coating composition according to claim 6 , wherein the crosslinked polyurethane is prepared by further adding at least one of the following crosslinkers (f), (g) and (d′):
(f) from 5 to 15 wt. % of at least one organic polyisocyanate with an average functionality of >2.3;
(g) from 2 to 7 wt. % of at least one polyol having a molecular weight of 500-5000 g/mol and an average functionality of at least 2.3;
(d′) at least one active-hydrogen chain extending compound with a functionality of 3 or higher in an amount of at least 50 wt. % of component (d), wherein
the amounts of (f), (g) and (d′) are given relative to the total amount of components (a), (b), (c), (d, including d′), (e), (f) and (g), used to prepare the polyurethane.
23. The aqueous coating composition according to claim 22 , wherein the polyol (g) has a glass transition temperature Tg from −110° C. to +110° C.
24. The aqueous coating composition according to claim 7 , wherein the total amount of (f), (g) and (d′) are together more than 5 wt. %, relative to the total amount of components (a), (b), (c), (d, including d′), (e), (f) and (g), used to prepare the polyurethane and the total amount of (f), (g) and (d′) are preferably together at most 20 wt. %, relative to the total amount of components (a), (b), (c), (d, including d′), (e), (f) and (g), used to prepare the polyurethane.
25. The aqueous coating composition according to claim 7 , wherein the total amount of (f), (g) and (d′) are together more than 10 wt. %, relative to the total amount of components (a), (b), (c), (d, including d′), (e), (f) and (g), used to prepare the polyurethane and the total amount of (f), (g) and (d′) are preferably together at most 20 wt. %, relative to the total amount of components (a), (b), (c), (d, including d′), (e), (f) and (g), used to prepare the polyurethane.
26. A process for preparing the aqueous coating composition according to claim 1 comprising the following steps:
a) reacting the components (a) to (c) to form a polyurethane;
b) optionally neutralising the polyurethane;
c) forming an aqueous dispersion of the polyurethane in water;
d) optionally adding at least one crosslinker (f), (g) and/or (d′);
e) adding at least a surfactant;
f) adding at least rheology additive;
g) adding vinyl monomer;
h) adding a radical initiator, wherein
steps b), c), d), e), f), g) and h) may be in any order.
27. A method of coating a substrate comprising (i) applying the aqueous coating composition according to claim 1 to a substrate and (ii) drying the aqueous coating composition by evaporation of volatiles, wherein the coating has a soft touch and wherein no additional chemical crosslinking reaction is needed to obtain the coating.
28. A coating having a soft touch which comprises the aqueous coating composition according to claim 1 .