Coating agent compositions that are suitable for dip coating and that cure at low temperature

Abstract

Aqueous coating compositions are provided. The aqueous compositions include at least one type of organic polymer particles having an average particle size of 10 to 1000 nm, including isocyanate-reactive polymers (A), one or more ketoxime- and/or pyrazole-blocked polyisocyanates (B) including at least one aromatic hydrocarbyl radical or at least one cycloaliphatic hydrocarbyl radical, at least one polyanionic polymer (C), at least one complex fluoride (D) selected from the group consisting of hexa- or tetrafluorides of metallic elements of groups IVb, Vb and VIb of the Periodic Table of the Elements, and at least one aminosilane (E), wherein the aqueous coating compositions have a pH of 3 to 5, and have a total solids content of 5% to 35% by weight. Also provided are processes for producing these aqueous coating compositions, processes for coating metal ion-releasing surfaces with the aqueous coating compositions, and coatings obtained therefrom.

Claims

1. An aqueous coating composition comprising at least one type of organic polymer particles having a Z-average particle size of 10 to 1000 nm, measured by means of dynamic light scattering, comprising isocyanate-reactive polymers (A), one or more ketoxime- and/or pyrazole-blocked polyisocyanates (B), comprising at least one aromatic hydrocarbyl group or at least one cycloaliphatic hydrocarbyl group, at least one polyanionic polymer (C), at least one complex fluoride (D) selected from the group consisting of hexa- or tetrafluorides of the metallic elements of groups IVb, Vb and VIb of the Periodic Table of the Elements, and at least one aminosilane (E) comprising a silyl group of the formula Si(OR.sup.7).sub.3-i(R.sup.8).sub.i in which R.sup.7 is an alkyl group having 1 to 4 carbon atoms or is an O═C—CH.sub.3 group, R.sup.8 is an alkyl group having 1 to 4 carbon atoms and i is 0 or 1, wherein the aqueous coating composition has a pH of 3 to 5, and has a total solids content (1 g sample, 60 min, 125° C.) of 5% to 35% by weight.

2. The aqueous coating composition according to claim 1, wherein the ketoxime- and/or pyrazole-blocked polyisocyanate(s) (B) is/are based on tolylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate and/or dicyclohexylmethane diisocyanate.

3. The aqueous coating composition according to claim 1, wherein the ketoxime- and/or pyrazole-blocked polyisocyanate(s) (B) comprise(s) polyethylene oxide chains and/or poly(ethylene oxide-propylene oxide) chains and/or an organic group comprising one or more sulfo groups, sulfonate groups, carboxyl groups and/or carboxylate groups.

4. The aqueous coating composition according to claim 1, wherein the polyanionic polymer (C) is selected from the group consisting of (C.i) naturally occurring anionic polysaccharides, naturally occurring polymers comprising acidic amino acids, (C.ii) semisynthetic polyanionic polysaccharides and lignosulfonates and (C.iii) fully synthetic polyanionic polymers.

5. The aqueous coating composition according to claim 1, wherein the polyanionic polymer (C) is selected from the group consisting of pectins, gellans, alginates and polyacrylic acids.

6. The aqueous coating composition according to claim 1, wherein the complex fluoride(s) (D) is/are selected from the group consisting of hexa- or tetrafluorides of titanium, zirconium or hafnium.

7. The aqueous coating composition according to claim 1, wherein the aminosilane (E) is an aminosilane of the general formula (VII)
H.sub.2N-L-Si(OR.sup.7).sub.3-i(R.sup.8).sub.i   (VII) in which L is a divalent organic connecting group; R.sup.7 is an alkyl group having 1 to 4 carbon atoms or is an O═C—CH.sub.3 group; R.sup.8 is an alkyl group having 1 to 4 carbon atoms; and i is 0 or 1.

8. The aqueous coating composition according to claim 1, wherein a content of the organic polymer particles comprising isocyanate-reactive polymers (A) is 3% to 25% by weight, based on a total weight of the aqueous coating composition; and/or a content of polyanionic polymers (C) is 0.01% to 5.0% by weight, based on the total weight of the aqueous coating composition; and/or an amount of the complex fluorides (D), based on a metal ion therein, is 1.1.Math.10.sup.−6 mol to 0.30 mol, in each case per liter of the aqueous coating composition; and/or a content of the aminosilanes (E) is 0.0005% to 1.0% by weight, based on the total weight of the aqueous coating composition.

9. The aqueous coating composition according to claim 1, wherein a molar ratio of blocked NCO groups of the ketoxime- and/or pyrazole-blocked polyisocyanates (B) to the isocyanate-reactive groups of the polymers (A) is between 0.5:1 and 2.0:1.

10. The aqueous coating composition according to claim 1, wherein a content of organic solvents is 0% to 15% by weight, based on the total weight of the aqueous coating composition.

11. A process for producing an aqueous coating composition as defined in claim 1, which comprises: either (i) mixing the ketoxime- and/or pyrazole-blocked polyisocyanate(s) (B), with or without use of an external emulsifier, with a dispersion of the organic polymer particles that have a Z-average particle size of 10 to 1000 nm, measured by means of dynamic light scattering, and comprise one or more isocyanate-reactive polymers (A); or (ii) preparing a dispersion of the organic polymer particles that have a Z-average particle size of 10 to 1000 nm, measured by means of dynamic light scattering, and comprise one or more isocyanate-reactive polymers (A) in the presence of the ketoxime- and/or pyrazole-blocked polyisocyanate(s) (B); and which further comprises (iii) mixing the polyanionic polymer(s) (C), the complex fluoride(s) (D) and the aminosilane(s) (E) into the mixture prepared in step (i) or the dispersion prepared in step (ii), either during or after preparation of the mixture in step (i) or during or after preparation of the dispersion in step (ii); and (iv) subsequently adjusting the pH of the mixture formed in step (iii) to a value of 3 to 5.

12. A process for coating a metal ion-releasing surface of a substrate, comprising the steps of: I. providing a substrate having a metal ion-releasing surface, II. contacting the metal ion-releasing surface with an aqueous coating composition according to claim 1 to form an organic coating, III. optionally rinsing the organic coating and IV. optionally drying the organic coating at a temperature of 10 to 120° C. within a period of 1 to 40 min; and curing the organic coating at a peak metal temperature of 120 to 200° C. within a period of 5 to 50 min; or V. optionally drying the organic coating and coating with a further aqueous coating composition according to claim 1 and then drying the coating formed in step V or both coatings; and curing the two coatings together at a peak metal temperature of 120 to 200° C. within a period of 5 to 50 min.

13. The process for coating a metal ion-releasing surface of a substrate according to claim 12, wherein the substrate is selected from a. metallic substrates, comprising metals and/or alloys, and metals and/or alloys and/or nonmetallic substrates that have been coated with metals and/or alloys; and b. nonmetallic substrates, comprising an underlying substrate coated with organic coatings and/or nonmetallic inorganic coatings, where metal ions have been incorporated into the coatings or metal ions released by the underlying substrate can diffuse through the coatings to the surface.

14. The process for coating a metal ion-releasing surface of a substrate according to claim 12, wherein said substrate, prior to performance of step II, is subjected to a surface pretreatment comprising one or more of the following measures: removing surface impurities; activating the surface for the coating in step II; and/or applying one or more corrosion-inhibiting and/or adhesion-promoting and/or metal ion-releasing layers.

15. A coating obtainable by the process according to claim 12.

Description

EXAMPLES

(1) Dip coating baths were filled with aqueous coating compositions according to the constituents specified in tables 1 to 4. The figures in the tables relate to parts by weight (of solids) in 100 parts by weight of the coating composition. All baths had a pH of 4.0±0.2 and a total solids content of 20.7±0.5% by weight (1 g of sample, 60 min, 125° C.).

(2) At room temperature (23° C.), alkali-cleaned Bonder sheets of cold-rolled steel were dipped into the corresponding baths for 1 min in order to coat the sheets.

(3) Subsequently, the coatings were rinsed with water and dried. The dry layer thickness after drying at 80° C. for 10 minutes was about 20 μm for all samples.

(4) On completion of drying, the sheets coated in accordance with the invention were baked at an object temperature (peak metal temperature; PMT) of 170 or 180° C. for 15 or 20 min.

(5) The samples were tested in the neutral salt spray test (NSS; according to DIN EN ISO 9227:2012-09). Undermining was averaged from multiple measurements in each case and classified into groups from “excellent” (+++) to “poor” (−) (see tables).

(6) The examples identified by an asterisk “*” in the tables are comparative examples.

Constituents of the Examples and Comparative Examples*

(7) A1 Organic polymer particles composed of a hydroxy-functional and hence isocyanate-reactive epoxy resin having an epoxy equivalent weight (VLN 305) of 485-550 g/mol and an average particle size of about 600 nm B1 DMP-blocked cycloaliphatic polyisocyanate having an NCO content of 14.2% by weight B2 DMP-blocked cycloaliphatic polyisocyanate having an NCO content of 20.3% by weight B3 MEKO-blocked cycloaliphatic polyisocyanate having an NCO content of 14.7% by weight B4 MEKO-blocked aromatic polyisocyanate based on MDI and having an NCO content of 19.0% by weight B5 DMP-blocked cycloaliphatic polyisocyanate containing a polyethylene oxide chain and having an NCO content of 10.5% by weight B6 MEKO-blocked cycloaliphatic polyisocyanate containing a polyethylene oxide chain and having an NCO content of 9.7% by weight C1 pectin (ammonium salt; pH of a 2.5% by weight aqueous solution at 20° C.: 2.5-4.5); having a number-average molecular weight M.sub.n of about 80 000 g/mol D1 hexafluorozirconic acid E1 aminopropyltriethoxysilane (AMEO) F1 preservative

(8) The results in table 1 show that it is possible using both hydrophobic and hydrophilic, cycloaliphatic and aromatic, pyrazole- and ketoxime-blocked polyisocyanates to form homogeneous coatings usable for simple applications from aqueous coating compositions that, after predrying at 80° C. for 10 min, show good to acceptable undermining resistance under baking conditions (15 min at 180° C.) at least under brief stress in the neutral salt spray test (168 h). No clear differences exist between hydrophilic and hydrophobic blocked polyisocyanates, and so both types can be employed in principle.

(9) TABLE-US-00001 TABLE 1 Example Example Example Example Example Example Constituents 1* 2* 3* 4* 5* 6* Organic polymer particles, comprising A1 13.57 15.01 13.71 14.76 12.17 11.78 isocyanate-reactive polymers (A) Blocked hydro- cyclo- DMP 14.2% NCO B1 6.43 polyiso- phobic aliphatic 20.3% NCO B2 4.99 cyanate MEKO 14.7% NCO B3 6.29 (B) aromatic MEKO 19.0% NCO B4 5.24 hydro- cyclo- DMP 10.5% NCO B5 7.83 philic aliphatic MEKO 9.7% NCO B6 8.22 Polyanionic polymer (C) C1 0.5 0.5 0.5 0.5 0.5 0.5 Complex fluorides (D) D1 0.05 0.05 0.05 0.05 0.05 0.05 Additive (F) F1 0.1 0.1 0.1 0.1 0.1 0.1 Predrying (10 min; 80° C.; on CRS) NCO.sup.(B)/ + + + + ∘ + Baking (15 min; 180° C. (PMT)) OH.sup.(A) ratio = 0.75 Undermining (NSS, 168 h) [mm] Under the above drying, baking and test conditions, undermining [in mm] of 5.0 to 8.5 is rated as “good” (+) and undermining [in mm] of 8.6 to 12.0 as “acceptable” (∘). The above formulations comprise: 0.9-1.4% by weight of methoxypropanol, 1.6-3.4% by weight of methoxypropyl acetate and 2.9-4.4% by weight of total solvents. MEKO: methyl ethyl ketoxime; DMP: 3,5-dimethylpyrazole; NCO.sup.(B): NCO group content in (B) in [mol]; OH.sup.(A): OH group content in (A) in [mol]

(10) By comparison with table 1, table 2 shows that good to acceptable undermining results are obtained even at a molar ratio of the blocked NCO groups of the blocked polyisocyanate (B) to the isocyanate-reactive OH groups of the polymer (A) of 1.0.

(11) TABLE-US-00002 TABLE 2 Example Example Example Example Constituents 7* 8* 9* 10* Organic polymer particles, comprising A1 12.26 13.85 12.41 13.57 isocyanate-reactive polymers (A) Blocked hydro- cyclo- DMP 14.2% NCO B1 7.74 polyiso- phobic aliphatic 20.3% NCO B2 6.15 cyanate aromatic MEKO 14.7% NCO B3 7.59 (B) MEKO 19.0% NCO B4 6.43 Polyanionic polymer (C) C1 0.5 0.5 0.5 0.5 Complex fluorides (D) D1 0.05 0.05 0.05 0.05 Additive (F) F1 0.1 0.1 0.1 0.1 Predrying (10 min; 80° C.) NCO.sup.(B)/OH.sup.(A) + + ∘ + Baking (15 min; 180° C. (PMT)) ratio = 1.0 Undermining (NSS, 168 h) [mm] Under the above drying, baking and test conditions, undermining [in mm] of 5.0 to 8.5 is rated as “good” (+) and undermining [in mm] of 8.6 to 12.0 as “acceptable” (∘).

(12) In table 3, at the same molar ratio of the blocked NCO groups of the blocked polyisocyanate (B) to the isocyanate-reactive OH groups of the polymer (A) of 1.0 as established in table 2, the baking conditions are varied to the effect that the baking operation is effected under underbaking conditions, i.e. at temperatures of 170° C. that typically, i.e. without addition of the silane (E), do not permit complete crosslinking within the given baking period (20 min) for the systems examined. Surprisingly, the inventive coatings of examples 12 and 14 obtained using the silane (E) nevertheless show good to acceptable, and in any case better, undermining results compared to the noninventive coatings of examples 11* and 13*.

(13) TABLE-US-00003 TABLE 3 (underbaking conditions) Example Example Example Example Constituents 11* 12 13* 14 Organic polymer particles, comprising A1 12.26 12.26 13.57 13.57 isocyanate-reactive polymers (A) Blocked hydro- cycloaliphatic DMP 14.2% NCO B1 7.74 7.74 polyisocyanate phobic aromatic MEKO 19.0% NCO B4 6.43 6.43 (B) Polyanionic polymer (C) C1 0.5 0.5 0.5 0.5 Complex fluorides (D) D1 0.05 0.05 0.05 0.05 Silane (E) E1 0.0 0.002 0.0 0.002 Additive (F) F1 0.1 0.1 0.1 0.1 Baking (20 min; 170° C. (PMT)) NCO.sup.(B)/OH.sup.(A) − ∘ ∘ + Undermining (NSS, 240 h) [mm] ratio = 1.0 Under the above drying, baking and test conditions, undermining [in mm] of 5.0 to 8.5 is rated as “good” (+), undermining [in mm] of 8.6 to 12.0 as “acceptable” (∘) and undermining [in mm] of greater than 12.0 as “poor” (−).

(14) By comparison with the experiments in table 3, the baking temperature in table 4 was increased again by 10° C. to 180° C. with the same baking time. Predrying was dispensed with. The undermining results after performance of the neutral salt spray test for 240 hours demonstrate that inventive examples 15 and 16 give very good to excellent results in the undermining test. The aqueous coating compositions of the invention are thus distinctly superior to the noninventive compositions even in the case of prolonged exposure in the neutral salt spray test.

(15) TABLE-US-00004 TABLE 4 Constituents Example 15 Example 16 Organic polymer particles, comprising isocyanate-reactive polymers (A) A1 13.57 10.20 Blocked hydrophobic aromatic MEKO 19.0% NCO B4 6.43 9.80 polyisocyanate (B) Polyanionic polymer (C) C1 0.5 0.5 Complex fluorides (D) D1 0.05 0.05 Silane (E) E1 0.002 0.002 Additive (F) F1 0.1 0.1 Baking (20 min; 180° C. (PMT)) NCO.sup.(B)/OH.sup.(A) ratio = ++ Undermining (NSS, 240 h) [mm] 1.0 NCO.sup.(B)/OH.sup.(A) ratio = +++ 1.5 Under the above drying, baking and test conditions, undermining [in mm] of less than 2.0 is rated as “excellent” (+++) and undermining [in mm] of 2.1 to less than 5.0 is rated as “very good” (++).