Aqueous dip-coating composition for electroconductive substrates, comprising bismuth and a phosphorus-containing, amine-blocked compound

Abstract

The present invention relates to an aqueous coating composition (A) comprising at least one cathodically depositable binder (A1) and optionally at least one crosslinking agent (A2), for at least partly coating an electrically conductive substrate with an electrocoat material, where (A) comprises a total amount of at least 30 ppm of bismuth, based on the total weight of (A), and additionally at least one phosphorus-containing compound (P) blocked with at least one amine of the general formula (I), to the use of (A) for at least partly coating an electrically conductive substrate with an electrocoat material, to a corresponding coating method, and to an at least partly coated substrate obtainable by this method.

Claims

1. An aqueous coating composition (A), comprising: (A1) at least one cathodically depositable binder; and (A2) optionally at least one crosslinking agent, for at least partly coating an electrically conductive substrate with an electrocoat material, wherein: the coating composition (A) comprises a total amount of at least 30 ppm of bismuth, based on a total weight of the coating composition (A); the coating composition (A) comprises at least one phosphorus-containing compound (P) blocked with at least one amine of the general formula (I): ##STR00004## R.sup.1 and R.sup.2 each independently of one another are a C.sub.1-18 aliphatic radical, are a C.sub.3-12 cycloaliphatic radical, are a C.sub.3-12 cycloaliphatic radical bridged via a C.sub.1-10 aliphatic group, or are an aryl or heteroaryl radical bridged via a C.sub.1-10 aliphatic group; and R.sup.3 is H, a C.sub.1-18 aliphatic radical, a C.sub.3-12 cycloaliphatic radical, a C.sub.3-12 cycloaliphatic radical bridged via a C.sub.1-10 aliphatic group, or an aryl or heteroaryl radical bridged via a C.sub.1-10 aliphatic group.

2. The coating composition (A) of claim 1, wherein the coating composition (A) has a pH ranging from 4.0 to 6.5.

3. The coating composition (A) of claim 1, comprising at least one phosphorus-containing compound (P), blocked with at least one amine of the general formula (I), in an amount of 0.05 to 5 wt %, based on the total weight of the coating composition (A).

4. The coating composition (A) of claim 1, wherein at least one of the radicals R.sup.1, R.sup.2, and R.sup.3 is a C.sub.1-18 aliphatic radical.

5. The coating composition (A) of claim 1, wherein at least one of the radicals R.sup.1, R.sup.2, and R.sup.3 is a C.sub.3-18 alkyl radical.

6. The coating composition (A) of claim 1, wherein R.sup.3 is a C.sub.1-18 aliphatic radical or is an aryl or heteroaryl radical bridged via a C.sub.1-10 aliphatic group.

7. The coating composition (A) of claim 1, wherein the phosphorus-containing compound (P) is selected from the group consisting of a phosphonic diester, a diphosphonic diester, a phosphoric monoester, a phosphoric diester, anions thereof and a mixture thereof.

8. The coating composition (A) of claim 1, wherein: the at least one phosphorus-containing compound (P) blocked with the at least one amine is obtained by reacting a phosphorus-containing compound (P) with an amine, and the phosphorus-containing compound (P) is a compound of the formula (II) or an anion thereof: ##STR00005## wherein R.sup.4 and R.sup.5 each independently of one another are selected from the group consisting of an unsubstituted (hetero)alkyl radical comprising 1 to 20 carbon atoms and optionally 1 to 4 heteroatoms selected from the group consisting of N, NH, N(C.sub.1-6 alkyl), O, and S, an unsubstituted (hetero)cycloalkyl radical comprising 3 to 20 carbon atoms and optionally 1 to 4 heteroatoms selected from the group consisting of N, NH, N(C.sub.1-6 alkyl), O, and S, and an unsubstituted (hetero)aryl radical comprising 5 to 20 carbon atoms and optionally 1 to 4 heteroatoms selected from the group consisting of N, NH, N(C.sub.1-6 alkyl), O, and S; and one of the radicals R.sup.4 and R.sup.5, or both radicals R.sup.4 and R.sup.5, may additionally be hydrogen.

9. The coating composition (A) of claim 1, wherein the bismuth in the coating composition (A) is present in a form in which it is in solution (A3) and/or not in solution (A4) in the coating composition (A).

10. The coating composition (A) of claim 1, wherein at least a part of the total amount of bismuth in the coating composition (A) is present in a form (A3) in which it is in solution in the coating composition (A).

11. The coating composition (A) of claim 1, wherein the total amount of bismuth present in the coating composition (A) is from 30 ppm to 20 000 ppm.

12. The coating composition (A) claim 1, wherein the coating composition (A) comprises the total amount of at least 130 ppm of bismuth, based on the total weight of the coating composition (A), including (A3) at least 100 ppm of bismuth, based on the total weight of the coating composition (A), in a form in which it is in solution in the coating composition (A), or (A3) at least 30 ppm of bismuth, based on the total weight of the coating composition (A), in a form in which it is in solution in the coating composition (A), and (A4) at least 100 ppm of bismuth, based on the total weight of the coating composition (A), in a form in which it is not in solution in the coating composition (A).

13. The coating composition (A) of claim 1, wherein the coating composition (A) further comprises (A5) at least one bidentate complexing agent suitable for complexing bismuth.

14. The coating composition (A) of claim 13, wherein the at least one complexing agent (A5) is present in the aqueous coating composition (A) in a fraction of at least 5 mol %, based on the total amount of bismuth present in the coating composition (A).

15. The coating composition (A) of claim 1, wherein the binder (A1) is a polymeric resin which has at least partly protonated tertiary amino groups, and the crosslinking agent (A2) present optionally is a blocked isocyanate.

16. The coating composition (A) of claim 15, wherein the tertiary amino groups each independently of one another have at least two C.sub.1-3 alkyl groups each at least singly substituted by a hydroxyl group.

17. A method, comprising at least partly coating an electrically conductive substrate with the aqueous coating composition (A) of claim 1 in the form of the electrocoat material.

18. A method for at least partly coating an electrically conductive substrate with an electrocoat material, the method comprising: (1) contacting the electrically conductive substrate, connected as cathode, with the aqueous coating composition (A) of claim 1.

19. The method of claim 18, wherein step (1) is carried out in at least two successive stages (1a) and (1b): (1a) at an applied voltage in a range from 1 to 50 V, which is applied for at least 5 seconds, and (1b) at an applied voltage in a range from 50 to 400 V, with the proviso that the voltage applied in (1b) is greater by at least 10 V than the voltage applied in (1a).

20. The method of claim 19, wherein the voltage applied in (1a) is applied for 5 to 300 seconds.

21. The method of claim 19, wherein the voltage in (1b) is applied for 0 to 300 seconds time intervals after implementation of (1a) and is maintained for 10 to 300 seconds at a value within the voltage range of 50 to 400 V.

22. An electrically conductive substrate coated at least partly with the aqueous coating composition (A) of claim 1.

23. The electrically conductive substrate of claim 22, wherein the substrate has at least one surface of aluminum.

24. An article or component produced from at least one electrically conductive substrate of claim 20.

Description

INVENTIVE AND COMPARATIVE EXAMPLES

(1) 1. Production of Inventive Aqueous Coating Compositions and of a Comparative Coating Composition

(2) The CathoGuard 520 pigment pastes from BASF that are used for producing the exemplary inventive coating compositions Z1 and Z2 below, and the comparative coating composition V1, contain bismuth subnitrate. The skilled person knows of the production of such pigment pastes from, for example, DE 10 2008 016 220 A1 (page 7, table 1, variant B).

(3) Comparative Coating Composition V1

(4) An aqueous dispersion of a binder and of a crosslinking agent (commercially available product CathoGuard 520 from BASF Coatings GmbH with a solids content of 37.5 wt %) (2130 parts) is mixed with fractions of deionized water (2497 parts) at room temperature (18-23 C.) to give a mixture M1. Added to this mixture M1 are a pigment paste (commercially available product CathoGuard 520 from BASF, with a solids content of 65.0 wt %) (306 parts) and a water-soluble compound containing bismuth(III) (67 parts), and the resulting mixture is mixed with stirring at room temperature (18-23 C.) to give a mixture M2. After further stirring over a time of 24 hours at room temperature (18-23 C.) the comparative coating composition (V1) is obtained accordingly. The water-soluble compound containing bismuth(III) that is used is bismuth L-(+)-lactate (Bi1), with a bismuth content of 11.9 wt %.

(5) The preparation of this Bi1 takes place as described hereinafter: a mixture of L-(+)-lactic acid (88 wt % strength) (613.64 g) and deionized water (1314.00 g) is introduced and heated to 70 C. with stirring. 155.30 g of bismuth(III) oxide is added to this mixture, during which the temperature of the resulting mixture may rise to up to 80 C. After an hour, a further 155.30 g of bismuth(III) oxide are added to this mixture, and again the temperature of the resulting mixture may rise to up to 80 C. After a further hour a further 155.30 g of bismuth(III) oxide are added to this mixture, and the resulting mixture is stirred for 3 hours more. This is followed by addition of 1003 g of deionized water with stirring. After this time, optionally, the resulting mixture is cooled to a temperature in the range from 30 to 40 C., if this temperature has not already been reached. The reaction mixture is subsequently filtered (T1000 depth filter) and the filtrate is used as Bi1. Parts in this context denote parts by weight in each case.

(6) Coating Composition Z1

(7) Inventive coating composition Z1 is prepared in analogy to the preparation of comparative coating composition V1, with the difference that, prior to the further stirring over a time of 24 hours at room temperature (18-23 C.), the mixture M2 is additionally admixed with 19.5 parts of a phosphorus-containing compound blocked with an amine, (P1). Parts here denote parts by weight in each case.

(8) P1 here is prepared by charging 49.75 parts of di-2-ethylhexyl phosphate (acid number 187.15 mg KOH/g) together with 119.17 parts of butyl di glycol to a three-neck flask fitted with stirrer, temperature probe, and dropping funnel, and stirring the resulting mixture at room temperature (18 to 23 C.) for an hour. Then 58.69 parts of tris(2-ethylhexyl)amine are added dropwise at a rate such that the temperature of the mixture does not exceed 60 C. After cooling of the mixture at room temperature (18 to 23 C.), stirring takes place for a further hour, and the resulting mixture is used as P1.

(9) Coating Composition Z2

(10) Inventive coating composition Z2 is prepared in analogy to the preparation of comparative coating composition V1, with the difference that, prior to the further stirring over a time of 24 hours at room temperature (18-23 C.), the mixture M2 is additionally admixed with 29 parts of a phosphorus-containing compound (P) blocked with an amine (blocked compound P1). Parts here denote parts by weight in each case.

(11) The preparation of P1 takes place as described in connection with coating composition Z1.

(12) Table 1 provides an overview of the resulting inventive aqueous coating compositions Z1 and Z2 and of the aqueous comparative coating composition V1:

(13) TABLE-US-00001 TABLE 1 Inventive examples Z1 and Z2 and comparative example V1 Z1 Z2 V1 CathoGuard 520/wt % 42.43 42.35 42.60 Bi1/wt % 1.33 1.33 1.34 Deionized water/wt % 49.75 49.65 49.94 Pigment paste CathoGuard 6.10 6.09 6.12 520/wt % P1/wt % 0.39 0.58

(14) 2. Production of Coated Electrically Conductive Substrates by Means of the Inventive Aqueous Coating Composition Z1 or Z2 or the Comparative Coating Composition V1

(15) The aqueous coating composition Z1 or Z2 or the comparative coating composition V1 is applied in each case as a dip coating to a metal test panel as substrate. Each of the compositions Z1 and V1 is applied after its preparation as described above to the respective substrate.

(16) The metal test panel (T1) used is aluminum (ALU), as an example of an electrically conductive substrate. Each of the two sides of the respective panel used has an area of 10.5 cm .Math.19 cm, giving an overall area of around 400 cm.sup.2.

(17) They are first of all cleaned in each case by immersion of the panels into a bath containing an aqueous solution comprising the commercially available products Ridoline 1565-1 (3.0 wt %) and Ridosol 1400-1 (0.3 wt %) from Henkel, and also water (96.7 wt %), for a time of 1.5 to 3 minutes at a temperature of 62 C. This is followed by mechanical cleaning (using fine brushes), after which the panels are again immersed into the bath for a time of 1.5 minutes.

(18) The substrates cleaned in this way are subsequently rinsed with water (for a time of 1 minute) and with deionized water (for a time of 1 minute).

(19) Immediately thereafter, an inventively employed aqueous coating composition Z1 or Z2 or the comparative coating composition V1 is applied to each panel T1, with the respective panel being immersed in each case into a corresponding dip-coating bath comprising one of the compositions Z1 or Z2 or V1. The dip-coating bath here has a respective temperature of 32 C.

(20) Coating in the dip-coating bath is carried out by means of a two-stage deposition step and coating step (1), which provides two stages (1a) and (1b), where first of all, potentiostatically, a voltage of 4 V is applied for a time of 120 seconds (corresponding to stage (1a)), to give a preliminary deposition of bismuth.

(21) Subsequently, for the substrates obtained after stage (1a), stage (1b) of step (1) of the method of the invention is carried out, with application of a voltage of 4 V potentiostatically, this being raised continuously and linearly to a voltage in the region of 160-200 V, in each case over a time of 30 seconds, by means of a voltage ramp. This respective voltage is then held for a time in the range from 60 to 180 seconds (hold time).

(22) In detail, for coating of the substrate T1 with one of the compositions V1 or Z1 or Z2, the following parameters are selected:

(23) V1:

(24) Stage (1a): 4 V over 120 seconds (potentiostatically) Stage (1b): voltage ramp: linear increase in voltage to 200 V over a time of 30 seconds and hold time of 180 seconds at this voltage

(25) Z1:

(26) Stage (1a): 4V over 120 seconds (potentiostatically) Stage (1b): voltage ramp: linear increase in voltage to 160 V over a time of 30 seconds and hold time of 60 seconds at this voltage

(27) Z2:

(28) Stage (1a): 4V over 120 seconds (potentiostatically) Stage (1b): voltage ramp: linear increase in voltage to 160 V over a time of 30 seconds and hold time of 60 seconds at this voltage

(29) The baking step that follows is accomplished by baking the resulting coatings in each case at 175 C. (oven temperature) for a time of 25 minutes. The dry film thicknesses of the aqueous coating compositions of the invention baked onto the respective substrates are in each case 20 m.

(30) 3. Investigation of the Anticorrosion Effect of the CSated substrates

(31) The substrate T1, coated with one of the coating compositions V1, Z1 or Z2, is investigated.

(32) All of the tests below were carried out in accordance with the aforementioned methods of determination and/or with the corresponding standard. Each value in table 3 is the average value (with standard deviation) from a double or triple determination.

(33) TABLE-US-00002 TABLE 3 Inv. Inv. Comp. Ex. Ex. ex. Substrate T1 T1 T1 (ALU) (ALU) (ALU) Coating composition Z1 Z2 V1 Maximum thread length 6.5 4.5 8.4 [mm] as per PAPP WT 3102 (Daimler) after filiform corrosion as per DIN EN 3365 after 1008 h Average thread, length 4.2 2.6 5.8 [mm] as per PAPP WT 3102 (Daimler) after filiform corrosion as per DIN EN 3365 after 1008 h

(34) As can be seen from table 3, the substrates coated by the method of the invention with an aqueous coating composition of the invention consistently exhibit an improved anticorrosion effect in comparison to the substrate coated with the comparative coating composition.