Aqueous coating compositions based on self-crosslinking polyurethane dispersions
The present invention is drawn to an aqueous polyurethane dispersion comprising: —anionic polyurethane particles comprising both free pending carboxylate groups of formula —COO − M + where M + is a cation resulting from neutralization of carboxylic acid groups with a base, and pending carboxylate ester groups resulting from esterification of free carboxylic acid groups with an epoxysilane, —crosslinking particles made of water-insoluble transition metal compounds. It is also drawn to a method of coating a substrate comprising applying such an aqueous polyurethane dispersion onto a substrate and letting it dry, preferably without applying any heat or radiation.
1 . An aqueous self-crosslinking polyurethane dispersion, comprising;
anionic polyurethane particles comprising both free pendant carboxylate groups of formula —COO − M + , wherein M + is a cation resulting from neutralization of carboxylic acid groups with a base, and pendant carboxylate ester groups resulting from esterification of free carboxylic acid groups with an epoxysilane; and
crosslinking particles comprising a water-insoluble transition metal compound, wherein the transition metal of the water-insoluble transition metal compound is selected from zinc, aluminum, tin, and tungsten.
2 . The aqueous polyurethane dispersion according to claim 1 , wherein the water-insoluble transition metal compound is selected from transition metal salts, transition metal oxides, and transition metal hydroxides.
3 . The aqueous polyurethane dispersion according to claim 1 , wherein a weight ratio of the crosslinking particles to the anionic polyurethane particles is 0.01 to 0.40.
4 . The aqueous polyurethane dispersion according to claim 3 , wherein the weight ratio of the crosslinking particles to the anionic polyurethane particles is 0.2 to 0.25.
5 . The aqueous polyurethane dispersion according to claim 3 , wherein the weight ratio of the crosslinking particles to the anionic polyurethane particles is 0.03 to 0.15.
6 . The aqueous polyurethane dispersion according to claim 1 , wherein the crosslinking particles have a weight average particle diameter, measured by laser diffraction, of 1.0 μm to 20 μm.
7 . The aqueous polyurethane dispersion according to claim 6 , wherein the weight average particle diameter of the crosslinking particles is 1.5 to 10 μm.
8 . The aqueous polyurethane dispersion according to claim 1 , wherein the epoxysilane is selected from the group consisting of 3-glycidyloxypropyl-trialkoxysilanes, 3-glycidyloxypropyl-dialkoxyalkylsilanes, epoxycyclohexylethyltrialkoxy-silanes, epoxycyclohexyl-ethyldialkoxyalkylsilanes, and water-soluble epoxysilane oligomers.
9 . The aqueous polyurethane dispersion according to claim 1 , further comprising from 0.1 to 70 weight % of mineral fillers.
10 . The aqueous polyurethane dispersion according to claim 9 , comprising from 1.0 to 40 weight % of the mineral fillers.
11 . The aqueous polyurethane dispersion according to claim 1 , further comprising a dispersing agent and/or a thickening agent.
12 . The aqueous polyurethane dispersion according to claim 11 , wherein the dispersing agent is a non-ionic surfactant and the thickening agent is a water-soluble organic polymer.
13 . The aqueous polyurethane dispersion according to claim 1 , wherein the amount of water is 30% to 95%.
14 . A method of preparing the aqueous polyurethane dispersion according to claim 1 , the method comprising:
esterifying pendant carboxylate groups of an anionic polyurethane dispersion by reacting them with an epoxysilane; and
dispersing water-insoluble transition metal compound particles in the anionic polyurethane dispersion.
15 . The method according to claim 14 , wherein the amount of epoxysilane used for esterification is 0.3 to 5.0% by weight with respect to the dry weight of the polyurethane dispersion.
16 . A method of coating a substrate, the method comprising:
applying the aqueous polyurethane dispersion according to claim 1 on a substrate and letting it dry.
17 . A water-proofing composition, a coating composition, an adhesive, or a sealant, comprising:
the aqueous polyurethane dispersion according to claim 1 .
18 . The aqueous polyurethane dispersion according to claim 1 , wherein the water-insoluble transition metal compound is a transition metal oxide.
19 . The aqueous polyurethane dispersion according to claim 1 , wherein the transition metal of the water-insoluble transition metal compound is selected from zinc and aluminum.