AQUEOUS COATING COMPOSITIONS BASED ON SELF-CROSSLINKING POLYURETHANE DISPERSIONS

Abstract

The present invention is drawn to an aqueous polyurethane dispersion comprising: —anionic polyurethane particles comprising both free pending carboxylate groups of formula —COO.sup.−M.sup.+ where M.sup.+ 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.

Claims

1. An aqueous polyurethane dispersion, comprising anionic polyurethane particles comprising both free pending carboxylate groups of formula —COO.sup.−M.sup.+, wherein M.sup.+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; and crosslinking particles made of water-insoluble transition metal compounds.

2. The aqueous polyurethane dispersion according to claim 1, wherein the water-insoluble transition metal compounds are selected from transition metal salts, transition metal oxides and transition metal hydroxides.

3. The aqueous polyurethane dispersion according to claim 1, wherein the transition metal is selected from the group consisting of zinc, aluminum, tin, and tungsten.

4. The aqueous polyurethane dispersion according to claim 1, wherein a weight ratio of the crosslinking particles to the anionic polyurethane particles is comprised between 0.01 and 0.40.

5. The aqueous polyurethane dispersion according to claim 1, wherein the crosslinking particles have a weight average particle diameter, measured by laser diffraction, comprised between 1.0 μm and 20 μm.

6. The aqueous polyurethane dispersion according to claim 1, wherein the epoxysilane is selected from the group consisting of 3-glycidyloxypropyl-trialcoxysilanes, 3-glycidyloxypropyl-dialcoxyalkylsilanes, epoxycyclohexylethyltrialcoxy-silanes, epoxycyclohexyl-ethyldialcoxyalkylsilanes, and water-soluble epoxysilane oligomers.

7. The aqueous polyurethane dispersion according to claim 1, further comprising from 0.1 to 70 weight %.

8. The aqueous polyurethane dispersion according to claim 1, further comprising a dispersing agent and/or a thickening agent.

9. The aqueous polyurethane dispersion according to claim 1, wherein the amount of water is comprised between 30% and 95% with respect to the total weight of the dispersion.

10. 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.

11. The method of according to claim 10, wherein the amount of epoxysilane used for esterification is comprised between 0.3 and 5.0% by weight with respect to the dry weight of the polyurethane dispersion.

12. 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.

13. A water-proofing composition, a coating composition, an adhesive, or a sealant, comprising: the aqueous polyurethane dispersion according to claim 1.

14. The aqueous polyurethane dispersion according to claim 1, wherein the water-insoluble transition metal compounds are transition metal oxides.

15. The aqueous polyurethane dispersion according to claim 1, wherein the transition metal is selected from the group consisting of zinc and aluminum.

16. The aqueous polyurethane dispersion according to claim 4, wherein the weight ratio of the crosslinking particles to the anionic polyurethane particles is comprised between 0.2 and 0.25.

17. The aqueous polyurethane dispersion according to claim 4, wherein the weight ratio of the crosslinking particles to the anionic polyurethane particles is comprised between 0.03 and 0.15.

18. The aqueous polyurethane dispersion according to claim 5, wherein the weight average particle diameter of the crosslinking particles is comprised between 1.5 and 10 μm.

19. The aqueous polyurethane dispersion according to claim 7, comprising from 1.0 to 40 weight % of the mineral fillers.

20. The aqueous polyurethane dispersion according to claim 8, wherein the dispersing agent is a non-ionic surfactant and the thickening agent is a water-soluble organic polymer.

Description

EXAMPLES

[0059] Four aqueous polyurethane dispersions having the compositions listed in Table 1 below were prepared as follows:

[0060] Example 1: An Aqueous Dispersion of an Anionic Polyurethane prepared from a polyether-polyol, aromatic diisocyanate, dimethylol propionic acid and ethylene-diamine as a chain extender was prepared. The resulting polyurethane dispersion (PUD) had a dry matter content of 42%, and an acid value of 16.1 mg KOH/g. 0.5% by weight 3-glycidyloxypropyl-triethoxysilane, with respect to the dry weight of PUD, was added drop-by-drop over a period of one hour to the PUD. The container was closed and the mixture was left to react for 72 hours without agitation. After 72-hour reaction, the dispersant and defoamer were added under agitation. After 5 minutes of agitation, the ZnO and fillers (barium sulfate, calcium carbonate) were added at once and dispersed by high speed mixing during 30 minutes. At the end, the viscosity was adjusted with a mixture of the remaining water, propyleneglycol and thickener (nonionic polyurethane associative thickeners).

[0061] The granulometric parameters of the ZnO particles are as follows: D.sub.90: 9.83 μm; D.sub.50: 3.35 μm, D.sub.10: 0.72 μm and D.sub.mean: 4.64 μm.

[0062] Comparative Example 2 was prepared as Example 1 except that the PUD was not reacted with 3-glycidyloxypropyl-triethoxysilane and no ZnO particles were incorporated into the dispersion.

[0063] Comparative Example 3 was prepared as Example 1 with the only difference that the PUD was not reacted with 3-glycidyloxypropyl-triethoxysilane.

[0064] Comparative Example was prepared as Example 1 with the only difference that no ZnO particles were incorporated into the composition.

TABLE-US-00001 TABLE 1 Example 1 Comparative Comparative Comparative (invention) Example 2 Example 3 Example 4 PUD 60 60 Epoxysilane- 60 60 PUD ZnO 3 3 Dispersant 0.1 0.1 0.1 0.1 Defoamer 0.5 0.5 0.5 0.5 Barium sulfate 10 10 10 10 Calcium 15 18 15 18 carbonate Talcum 5 5 5 5 Monopropyl- 1 1 1 1 eneglycol Thickener 2 2 2 2 Water 3.4 3.4 3.4 3.4

[0065] The polyurethane dispersions were then coated onto a polyethylene film in a wet thickness of 1 mm and were let to dry/cure for 7 or 28 days at room temperature. The coatings were then peeled off the polyethylene substrate and the membranes were cut into samples. The membranes dried for 7 days were then weighed, immersed in distilled water at room temperature for 24 hours or 14 days, weighed again and the weight increase (water uptake) was calculated and expressed with respect to the initial dry weight of the sample. The mechanical properties, i.e. elongation at break (EaB) and tensile strength (TS), before and after water immersion were measured according to ASTM D412.

[0066] The results are depicted in Table 2

TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 EaB after 7 372% 340% 350% 360% days of curing EaB after 28 305% 285% 320% 335% days of curing TS after 7 5.40 MPa 3.20 MPa 3.70 MPa 3.90 MPa days of curing TS after 28 5.45 MPa 3.95 MPa 4.10 MPa 4.30 MPa days of curing Water uptake  0.5% 7.61%  7.25%  6.43%  after 24 h immersion Water uptake  2.0% 18.0%  12.0%   9.0% after 14 days immersion EaB after 48 h 410% 810% 620% 600% immersion TS after 48 h 4.91 MPa 2.70 MPa 3.40 MPa 4.05 MPa immersion EaB after 14 546% 950% 750% 710% days of immersion TS after 14 4.52 MPa 2.40 Mpa 3.20 Mpa 3.90 MPa days of immersion

[0067] It can be seen that the polyurethane membrane of Example 1 cures much faster than those of the Comparative Examples 2-4. Its tensile strength hardly increases after only 7 days of curing.

[0068] The membrane of Example 1 further takes up much less water. Its water uptake after 24 h of immersion is nearly identical to the water uptake of a one-component solvent-based polyurethane resin (Mariseal® 250 from Maris Polymers) tested under same conditions.

[0069] Most importantly the mechanical performances of the polyurethane membrane of the invention (Example 1) deteriorate far less during immersion than those of the membranes of Comparative Examples 2-4.

[0070] These experimental examples thus show that the combined use of an epoxysilane and of crosslinking particles of transition metal compound particles results in a non-toxic, solvent free, non-flammable, stable film-forming polyurethane dispersion which, when coated onto a substrate, forms water-resistant coatings that display good maintenance of their mechanical performances.