Stain resistant urethane-vinyl aqueous coating compositions
View Patent ↗An aqueous coating composition, which when in the form of a film exhibits an MVTR of ≦500 g/m 2 /24 h comprising 20 to 80 wt % of a polyurethane A with an acid value of 8 to 40 mg KOH/g and a hard segment content ≧40 wt %, a ring structure content ≧48 wt % and 80 to 20 wt % of a vinyl polymer B with a Tg≧20° C.
1. An aqueous coating composition comprising:
(i) 20 to 80 wt % of a polyurethane A obtained by the reaction of:
(a) an isocyanate-terminated prepolymer formed from components comprising:
(1) 20 to 80 wt % of at least one polyisocyanate;
(2) 3 to 10 wt % of at least one isocyanate-reactive polyol of weight average molecular weight <500 Daltons, containing at least one ionic or potentially ionic water-dispersing group;
(3) 0 to 15 wt % of at least one isocyanate-reactive polyol containing non ionic water-dispersing groups;
(4) 17 to 77 wt % of at least one isocyanate-reactive polyol other than (3) having a weight average molecular weight within a range of 500 to 8000 Daltons and a ring structure content >30 wt. %;
(5) 0 to 20 wt % of at least one isocyanate-reactive polyol other than (2) or (3) of weight average molecular weight 500 Daltons;
where (1), (2), (3), (4) and (5) add up to 100%;
wherein the polyols (a)(3) to (5) have a total ring structure content 48 wt %; and
(b) an active-hydrogen chain extending compound;
wherein polyurethane A has an acid value in the range of from 8 to 40 mg KOH/g and a hard segment content ≧40 wt % by weight of polyurethane A; and
(ii) 80 to 20 wt % of a vinyl polymer B with a glass transition temperature ≦20° C., wherein vinyl polymer B comprises vinyl monomers comprising in total ≦70 wt % carbon, nitrogen and halogen based on vinyl monomer molecular weight; wherein
(i) and (ii) add up to 100%; and wherein
a film having a wet film thickness of 12 microns formed of the composition exhibits a moisture vapour transmission rate of ≦500 g/m 2 /24 h.
2. An aqueous coating composition according to claim 1 wherein polyurethane A has a weight average molecular weight in the range of from 50,000 to 1,000,000 Daltons.
3. An aqueous coating composition according to claim 1 wherein the acid value of vinyl polymer B is ≦10 mg KOH/g polymer.
4. An aqueous coating composition according to claim 1 wherein the vinyl polymer B has been formed using a multistage polymerisation process to form two or more vinyl polymer phases of different compositions.
5. An aqueous coating composition according to claim 4 wherein there is a difference in Tg values between at least two vinyl polymer phases of ≧20° C.
6. An aqueous coating composition according to claim 1 wherein vinyl polymer B has a weight average molecular weight in the range of from 50,000 to 6,000,000 Daltons.
7. An aqueous coating composition according to claim 1 wherein vinyl polymer B has been formed in the presence of polyurethane A.
8. An aqueous coating composition according to claim 1 further comprising a radiation curable multifunctional material.
9. An aqueous coating composition according to claim 8 where the radiation curable multifunctional material is selected from the group consisting of epoxy(meth)acrylates, urethane (meth)acrylates, multifunctional (meth)acrylate monomers, uv curable urethane dispersions and amine-(meth)acrylate adducts.
10. An aqueous coating composition according to claim 1 which further comprises a pigment.
11. An aqueous coating composition according to claim 10 with a pigment volume concentration of from 10 to 35%.
12. An aqueous coating composition according to claim 1 which is substantially solvent free.
13. A process for the manufacture of an aqueous coating composition according to claim 1 which comprises the following steps:
(I) (i) reaction of components (a)(1) to (a)(5) together to form an isocyanate-terminated prepolymer;
(ii) neutralisation of the isocyanate-terminated prepolymer;
(iii) dispersion of the isocyanate-terminated prepolymer in water;
(iv) chain extension of the isocyanate-terminated prepolymer by reaction with an active-hydrogen chain extending compound to form polyurethane A; and
(II) admixture of preformed vinyl polymer B.
14. A process for the manufacture of an aqueous coating composition according to claim 1 which comprises the following steps:
(I) (i) reaction of components (a)( 1 ) to (a)( 5 ) to form an isocyanate-terminated prepolymer;
(ii) neutralisation of the isocyanate-terminated prepolymer;
(iii) dispersion of the isocyanate-terminated prepolymer in water;
(iv) chain extension of the isocyanate-terminated prepolymer by reaction with an active-hydrogen chain extending compound to form polyurethane A;
(II) admixture of vinyl monomer followed by reaction under conditions sufficient to effect emulsion polymerisation to form vinyl polymer B.
15. A film obtained from an aqueous coating composition according to claim 1 .
16. A coating obtained from an aqueous coating composition according to claim 1 .
17. A method of coating the surfaces of a substrate comprising application of an aqueous coating composition according to claim 1 to the substrate.
18. A method of coating according to claim 17 wherein the substrate is porous.
19. A method of coating according to claim 17 wherein the substrate is wood.