Radiation curable aqueous dispersions

1. A stable radiation curable aqueous dispersion comprising a mixture of a first dispersion and a second dispersion, and a photoinitiator,

wherein said first dispersion comprises at least one (meth)acrylated pre-polymer (A) and, optionally, at least one ethylenically unsaturated compound (C), and

said second dispersion comprises at least one thiol-functional compound (B) and is different from said first dispersion,

wherein an equivalent ratio between (i) a concentration of thiol groups and (ii) a concentration of meth(acrylate) groups and, if present, of ethylenically unsaturated groups is 0.30 or less, wherein said concentrations are expressed in milli-equivalents per gram of solid contained in said aqueous dispersion,

wherein said first dispersion comprises dispersed particles having a global positive or negative charge and said second dispersion comprises dispersed particles having a global charge with the same sign as said dispersed particles of said first dispersion,

wherein the dispersed particles of the first dispersion are different from the dispersed particles of the second dispersion,

wherein the at least one ethylenically unsaturated compound (C) is at least one (poly)(meth)acryloyl-containing compound,

wherein said (meth)acrylated pre-polymer (A) is selected from (meth)acrylated (poly)urethane pre-polymers (A) obtained from the reaction of:

at least one polyisocyanate compound (ia),

optionally, at least one polyol (iia),

at least one hydrophilic compound (iiia) containing at least one reactive group capable of reacting with isocyanate groups, said hydrophilic compound (iiia) being capable of rendering the (poly)urethane pre-polymer dispersible in aqueous medium either directly or after a reaction with a neutralizing agent to provide a salt,

at least one (meth)acrylated compound (iva) containing at least two reactive groups capable of reacting with isocyanate groups, and

at least one (meth)acrylated compound (va) containing one reactive group capable of reacting with isocyanate groups, and

wherein said at least one thiol-functional compound (B) comprises at least one thiol-functional (poly)urethane pre-polymer (B1) which carries groups which impart water dispersibility to the (poly)urethane and/or at least one thiol-functional pre-polymer (B2) which carries groups which impart water dispersibility to the pre-polymer (B2), and which is prepared from monomers capable of free radical polymerization and having C═C double bonds by the method of free radical mass or solution polymerization,

the thiol-functional (poly)urethane pre-polymer (B1) and the thiol-functional pre-polymer (B2) carrying from 0.05 to 5 meq of thiol groups per gram of thiol-functional (poly)urethane pre-polymer (B1) or thiol-functional pre-polymer (B2) respectively.

2. The stable aqueous dispersion according to claim 1 , wherein a total amount of (meth)acrylated groups in the pre-polymer (A) is at least 3.0 meq of (meth)acrylated groups per total weight in grams of compounds (ia), (iia), (iiia), (va) and (iva).

3. The stable aqueous dispersion according to claim 2 , wherein the total amount of (meth)acrylated groups in the pre-polymer (A) is at least 3.5 meq of (meth)acrylated groups per total weight in grams of compounds (ia), (iia), (iiia), (va) and (iva).

4. The stable aqueous dispersion according to claim 1 , wherein the (poly)urethane pre-polymer (B1) is obtained from the reaction of:

at least one polyisocyanate compound (ib),

at least one polyol (iib),

at least one hydrophilic compound (iiib) containing at least one reactive group capable of reacting with isocyanate groups, said hydrophilic compound (iiib) being capable of rendering the (poly)urethane pre-polymer (B1) dispersible in aqueous medium either directly or after a reaction with a neutralizing agent to provide a salt, and

at least one compound (ivb) containing at least two functional groups of which a first functional group is a thiol group and a second functional group is a reactive group capable of reacting with an isocyanate group.

5. The stable aqueous dispersion according to claim 1 , wherein said second dispersion comprises an admixture of:

(i) at least one polyurethane polymer (J1) which carries groups which impart water dispersibility to the polyurethane (J1) and/or at least one polymer (J2) which carries groups which impart water dispersibility to the polymer (J2), prepared from monomers capable of free radical polymerization and having C═C double bonds by the method of free radical mass or solution polymerization, the polyurethane polymer (J1) and the polymer (J2) comprising less than 0.05 meq of thiol groups per gram; and

(ii) at least one thiol-functional compound (B3) comprising at least two thiol groups, said compound (B3) having a solubility of at most 1 g/l in water and a molecular weight of less than 10000.

6. The stable aqueous dispersion according to claim 1 , wherein the thiol-functional compound (B) of the second dispersion is different from the (meth)acrylated pre-polymer (A) of the first dispersion.

7. The stable aqueous dispersion according to claim 1 , wherein the equivalent ratio between (i) the concentration of thiol groups and (ii) the concentration of meth(acrylate) groups and, if present, of ethylenically unsaturated groups is 0.18 or less, wherein said concentrations are expressed in milli-equivalents per gram of solid contained in said aqueous dispersion.

8. A coating composition, ink, varnish or adhesive prepared from the stable aqueous dispersion according to claim 1 .

9. An article coated or treated, either entirely or in part, with the coating composition, ink, varnish or adhesive according to claim 8 .

10. A process for preparing a coated article comprising a step wherein at least one surface of the article is coated or treated with the stable aqueous dispersion according to claim 1 .

11. The process according to claim 10 , further comprising a step of irradiating said coated article with a UV-light source emitting in a spectrum having the strongest wavelengths between 350 nm and at 450 nm.

12. A process for the preparation of the stable aqueous dispersion according to claim 1 comprising:

preparing said first dispersion,

preparing said second dispersion, and

mixing said first dispersion with said second dispersion.