Chromium-free coating composition with anti-corrosive effect for metallic substrates

Abstract

The present disclosure relates to a chromium-free coating composition including at least one binder and at least one iron(III)-tris(N,N-dithiocarbamate) complex, where the binder includes at least one synthetic resin and at least one crosslinker. The present disclosure also relates to the use of such a coating composition for the protection against corrosion of metallic substrates, a process for at least partially coating a metallic substrate with such a priming coat, a substrate at least partially coated therewith and an article or a component made of such a substrate.

Claims

1. An aqueous chromium-free coating composition comprising at least one binder comprising at least one synthetic resin and at least one crosslinker, at least one iron(III)-tris(N,N-dithiocarbamate) complex of the general formula (I) [R.sup.1—N(—R.sup.2)—C(═S)—S].sub.3Fe.sup.+III wherein (i) R.sup.1 and R.sup.2, independently comprise a univalent linear, branched or cyclic aliphatic hydrocarbon radical with 1 to 10 carbon atoms; or (ii) R.sup.1 comprises a divalent linear or branched aliphatic hydrocarbon radical with 1 to 10 carbon atoms, R.sup.2 represents a covalent bond and R.sup.1 is linked by the covalent bond with the nitrogen atom of formula (I); and wherein the water content in the coating composition is at least 50.0 wt. % based on the total content of liquid diluents present in the coating composition; and wherein the binder comprises at least one epoxide resin and at least one crosslinker having at least one functional amino group.

2. The coating composition of claim 1, wherein the iron(III)-tris(N,N-dithiocarbamate) complex has a solubility in water at 20° C. of less than 0.1 mol/L.

3. The coating composition of claim 1, wherein the iron(III)-tris(N,N-dithiocarbamate) complex is present in an amount in the range of 0.01 to 25 wt. %, based on the non-volatile content of the coating composition as determined according to DIN EN ISO 3251 dated June 2008.

4. The coating composition of claim 1, wherein the at least one iron(III)-tris(N,N-dithiocarbamate) complex is selected from the group consisting of: iron(III)-tris(dimethyl dithiocarbamate), iron(III)-tris(diethyl dithiocarbamate) and iron(III)-tris(pyrrolidine dithiocarbamate).

5. The coating composition of claim 1, wherein the at least one epoxide resin has an epoxide equivalent weight in a range of 100 to 300, as determined according to DIN EN ISO 3001 dated November 1999.

6. The coating composition of claim 1, wherein the coating compositing is configured for protection against corrosion of metallic substrates.

7. The coating composition of claim 6, wherein the metallic substrates comprise metallic substrates within the area of aircraft manufacturing.

8. A process for at least partially coating a metallic substrate with a priming coat comprising, at least partially contacting the metallic substrate with the coating composition comprising at least one binder comprising at least one crosslinker; at least one iron(III)-tris(N,N-dithiocarbamate) complex of the general formula (I) comprising [R.sup.1—N(—R.sup.2)—C(═S)—S].sub.3Fe.sup.+III wherein (i) R.sup.1 and R.sup.2, independently comprise a univalent linear, branched or cyclic aliphatic hydrocarbon radical with 1 to 10 carbon atoms; or (ii) R.sup.1 comprises a divalent linear or branched aliphatic hydrocarbon radical with 1 to 10 carbon atoms, R.sup.2 represents a covalent bond and R.sup.1 is linked the covalent bond with the nitrogen atom of formula (I); and wherein the water content in the coating composition is at least 50.0 wt. % based on the total content of liquid diluents present in the coating composition.

9. The process of claim 8 wherein at least partially contacting the metallic substrate with the coating composition comprises at least partially applying a priming coat on the substrate; and applying at least one further layer, comprising a top coat layer or a clear coat layer, on the priming coat.

10. The process of claim 8, wherein before at least partially contacting the metallic substrate with the coating composition, the metallic substrate is pretreated with a tartaric acid-sulfuric acid-anodization (TSA) according to DIN EN 4704.

11. The process of claim 8, wherein the metallic substrate is an aluminium alloy of the group 2XXX or 7XXX.

12. A metallic substrate coated at least partially with a coating composition the coating composition comprising: at least one binder comprising at least one crosslinker; at least one iron(III)-tris(N,N-dithiocarbamate) complex of the general formula (I) comprising [R.sup.1—N(—R.sup.2)—C(═S)—S].sub.3Fe.sup.+III wherein (i) R.sup.1 and R.sup.2, independently comprise a univalent linear, branched or cyclic aliphatic hydrocarbon radical with 1 to 10 carbon atoms; or (ii) R.sup.1 comprises a divalent linear or branched aliphatic hydrocarbon radical with 1 to 10 carbon atoms, R.sup.2 represents a covalent bond and R.sup.1 is linked by means of the covalent bond with the nitrogen atom of formula (I); and wherein the water content in the coating composition is at least 50.0 wt. % based on the total content of liquid diluents present in the coating composition.

Description

EXAMPLES

Example 1

Testing Methods

(1) 1.1 Determination of the Non-Volatile Content

(2) The determination of the non-volatile content takes place according to DIN EN ISO 3251 (date: June 2008). In this process 1 g sample is weighed into a previously dried aluminium dish and dried for 60 minutes at 130° C. in a drying cabinet, cooled in a desiccator and then recovered. The residue based on the total amount of the used sample corresponds to the non-volatile content.

(3) 1.2 Neutral Salt Spray Mist Test

(4) The determination of the anti-corrosive effect of coats on a sample plate takes place with the neutral salt spray mist test (also known as salt spray test) following DIN EN ISO 9227:2012 DE. To this end two scratches are made with a cutter in cross-section on the metallic substrate coated with a coating composition or a comparative coating composition through the coat down to the substrate. In the test over a period of 3,000 h a 5% aqueous sodium chloride solution with a pH-value of the deposit of 6.5 to 7.2 (at 25±2° C.) at a test room temperature of 35±2° C. acts on the incised sample table. The dry film thickness of the coat is to be given in [μm]. Evaluated is the anti-corrosive effect according to the length of the penetration under the coat at the scratch.

(5) 1.3 Filiform Corrosion Test

(6) The determination of the filiform corrosion serves to establish the resistance to corrosion of a coat on a substrate. This determination is carried out following DIN EN ISO 4623-2:2004-06 DE for the metallic substrate coated with a coating composition according to the various embodiments herein or comparative coating composition over a duration of 504 h and 1,008 h. In that process the coat in question, starting from linear damage to the coat, is penetrated in the form of a linear or filiform under-surface corrosion. The length of the longest thread and the average thread length in [mm] in that case are measured out according to ISO 4628-10. The length of the longest thread and the average thread length are a measure of the coat's resistance to corrosion.

Example 2

Preparation of iron(III)-tris(N,N-dithiocarbamate) Complexes (B)

(7) For the preparation of iron(III)-tris(N,N-dimethyl dithiocarbamate) 200 mL of a 0.86 molar aqueous iron(III)nitrate nonahydrate solution in 300 mL of a 1.9 molar aqueous solution of sodium-dimethyl dithiocarbamate hydrate (CAS: 207233-95-2) was added dropwise and vigorously stirred for at least 6 h at a temperature of 15-25° C. After filtration over a traditional paper filter and drying at 40° C. a yield of >95% was obtained.

(8) Iron(III)-tris(N,N-diethyl dithiocarbamate) was prepared corresponding to the above procedure, but instead of an aqueous solution of sodium-dimethyl dithiocarbamate hydrate an aqueous solution of sodium-diethyl dithiocarbamate trihydrate (CAS: 20624-25-3) was used. A yield of >90% was obtained.

(9) Iron(III)-tris(N,N-pyrolidine dithiocarbamate) was prepared corresponding to the above procedure, but instead of an aqueous solution of sodium-dimethyl dithiocarbamate hydrate an aqueous solution of ammonium-pyrolidine dithiocarbamate (CAS: 5108-96-3) was used. A yield of >90% was obtained.

(10) The molar ratio of iron(III) to the appropriate sodium or ammonium salt of the dithiocarbamate complex in that case was set at 1 to 3.3.

Example 3.1

Preparation of Coating Compositions V1 to V5 Not According to the Various Embodiments Herein

(11) The two components of the coating compositions V1 to V5 not according to the various embodiments herein were prepared as follows (Table 1): positions 1-5 were presented and predispersed 15 min, after which positions 6-12, where applicable, were added with stirring. After that, the mixture was dispersed for 30 min at maximum 50° C. to a granularity of less than 20 μm, measured with a Grindometer according to Hegman (ISO 1524), by means of a pearl mill. Positions 13 and 14 of component 1 were stirred in after the dispersion. The ingredients of component 2 were added together in the specified sequence and intimately mixed, after which the two components of the coating composition were mixed shortly before use.

(12) TABLE-US-00001 TABLE 1 preparation of coating compositions V1 to V5 not according to the various embodiments herein Pos. Ingredient V1 V2 V3 V4 V5 component 1  1 Waterpoxy ® 751 17.75 17.75 17.75 17.75 17.75  2 TMDD ® BG 52 1.90 1.90 1.90 1.90 1.90  3 Butyl glycol 0.63 0.63 0.63 0.63 0.63  4 AMP-90 ® 0.13 0.13 0.13 0.13 0.13  5 VE-water 13.79 13.79 13.79 13.79 13.79  6 Lucenac ® 10MO 9.83 9.02 8.21 8.90 7.97  7 Aluminium silicate ASP 600 8.77 8.04 7.32 7.94 7.11  8 Titanium rutile 2310 12.84 11.78 10.72 11.62 10.40  9 Novacite ® L-207 A 2.56 2.35 2.14 2.32 2.07 10 Sillitin ® N 85 3.95 3.62 3.30 3.58 3.20 11a Sodium-dimethyl 3.14 6.27 dithiocarbamate 11b Ammonium-pyrrolidine 3.60 7.20 dithiocarbamate 12 Che ® Coat DF 0682 0.19 0.19 0.19 0.19 0.19 13 VE-water 5.69 5.69 5.69 5.69 5.69 14 Byk ® 346 0.63 0.63 0.63 0.63 0.63 component 2 15 Bisphenol-A-diglycidyl ether. 13.34 13.34 13.34 13.34 13.34 M.sub.w < 700 g/mol 16 Silquest ® A-187 1.86 1.86 1.86 1.86 1.86 17 Butyl acetate 5.07 5.07 5.07 5.07 5.07 18 water 25.0 25.0 25.0 25.0 25.0

(13) Waterpoxy® 751 is a commercially available amine adduct dissolved in water ex BASF. It has a solids content of 59 wt. %, based on its total weight.

(14) TMDD® BG 52 is the trade designation for 2,4,7,9-tetramethyl-5-decin-4,7-diol, a commercially available surfactant ex BASF which acts as foam inhibitor or rather as wetting agent.

(15) AMP-90® is the trade designation for 2-amino-2-methyl-1-propanol with 10% water ex Angus-Chemie GmbH, which serves as dispersion aid.

(16) Lucenac® 10MO is a commercially available talcum ex Luzenac Europe SAS.

(17) Novacite® L-207 A is a commercially available filler ex Malvern Minerals Co.

(18) Sillitin® N 85 is a filler on silica-kaolinite basis, commercially available ex Hoffmann Mineral.

(19) Che® Coat DF 0682 is a commercially available defoaming agent ex Erbslöh.

(20) Byk® 346 is a commercially available wetting agent ex BYK with a solids content of 52 wt. %.

(21) Silquest® A-187 is based on glycidoxypropyl trimethoxysilane and is commercially available ex Momentive with a solids content of 52 wt. %.

(22) The coating composition V1 thus is free of any dithiocarbamate, while V2-V3 and V4-V5, respectively, contain readily soluble dithiocarbamates not to be used in the embodiments herein.

(23) 3.2 Preparation of Substrates Coated with Coating Compositions V1 to V5 Not According to the Various Embodiments Herein

(24) Each time one of the coating compositions V1 to V5 not according to the various embodiments herein is applied as primer coating on a table of a commercially available aluminium alloy (EN AW 2024, substrate T3 clad, where the clad layer is a cladding of purest aluminium) as substrate.

(25) The sheets used in each case have a total surface of about 70 cm.sup.2. Each sheet was pretreated by means of a tartaric acid-sulfuric acid-anodization (TSA) according to DIN EN 4704 (date: May 2012).

(26) On each substrate (T3) is applied on one side one of the coating compositions V1 to V5 not according to the various embodiments herein by means of spraying with a spray gun.

(27) The dry film thickness in each case is 14-20 μm.

(28) 3.3. Investigation of the Anti-Corrosive Effect of Substrates Coated with Coating Compositions V1 to V5 Not According to the Various Embodiments Herein

(29) The previously described substrates T3V1, T3V2, T3V3, T3V4 and T3V5 coated with one of the coating compositions V1 to V5 were examined for their corrosion inhibition.

(30) To prepare for the neutral salt spray mist test the thus coated tables were stored 7 days at 15-25° C., after which a cross cut with a width of 1 mm in a depth of 300 μm was scored.

(31) To prepare for the filiform corrosion test the thus coated tables were stored 24 h at 15-25° C., whereupon a top coat layer (D1) was applied in a dry film thickness of 50 to 70 μm to obtain the coated sheets T3V1D1, T3V2D1, T3V3D1, T3V4D1 and T3V5D1. For application of the top coat layer in each case the commercial product Glasurit® of series 68 (RAL 9010), a 2K-polyurethane-based top coat, was used. The subsequent drying or rather curing took place by means of a storing of the coated sheets for a duration of 7 days at 15-25° C.

(32) The neutral salt spray mist test and the filiform corrosion test were carried out in a test sequence corresponding to the above-indicated determination methods. The results are given in Tables 2 and 3, wherein each value is the average value of a dual determination, standardized to the result of T3V1.

(33) TABLE-US-00002 TABLE 2 Results of the neutral salt spray mist test on 2024-T3-clad substrates coated with one of the coating compositions V1 to V5 not according to the various embodiments herein Substrate Penetration in the neutral salt spray mist test, composition after 3,000 h T3V1 1.0 T3V2 1.6 T3V3 1.1 T3V4 1.7 T3V5 1.0

(34) TABLE-US-00003 TABLE 3 Results of the filiform corrosion test on 2024-T3-clad substrates coated with one of the coating compositions V1 to V5 not according to the various embodiments herein and a top coat D1. Substrate Penetration in filiform corrosion test composition 504 h 1,008 h T3V1D1 1.0 1.0 T3V2D1 2.35 2.87 T3V3D1 2.39 3.08 T3V4D1 2.02 2.82 T3V5D1 1.67 2.57

(35) The results of Tables 2 and 3 show unequivocally that in comparison with coating composition V1, which is free of dithiocarbamates, adding readily water-soluble sodium-dimethyl dithiocarbamate (V2-V3) and moderately soluble ammonium-pyrrolidine dithiocarbamate (V4-V5), respectively, to the coating compositions leads to a clearly worse anti-corrosive effect, at best to one comparable to V1. The interaction of the readily or moderately water-soluble dithiocarbamates with the binder matrix of the coating composition thus appears to be unfavorable.

Example 4.1

Preparation of Coating Compositions E1 to E3 According to the Various Embodiments Herein and Comparative Coating Composition V6

(36) The two components of the coating compositions E1 to E3 according to the various embodiments herein and the comparative coating composition V6 were prepared by adding the respective ingredients together in the specified sequence and intimately mixing them in a dissolver (Table 4).

(37) The two components of the coating compositions E1 to E3 according to the various embodiments herein and the comparative coating composition V6 were prepared as follows (Table 4): positions 1-5 were presented and predispersed for 15 min, after which positions 6-12, where applicable, were added with stirring. After that, the mixture was dispersed for 30 min at maximum 50° C. to a granularity of less than 20 μm, measured with a Grindometer according to Hegman (ISO 1524), by means of a pearl mill. Positions 13 and 14 of component 1 were stirred in after the dispersion. The ingredients of component 2 were added together in the specified sequence and intimately mixed, after which the two components of the coating composition were mixed shortly before use.

(38) TABLE-US-00004 TABLE 4 Preparation of coating compositions E1-E3 according to the various embodiments herein and comparative coating composition V6. Pos. Ingredient V6 E1 E2 E3 component 1  1 Waterpoxy ® 751 14.59 14.59 14.59 14.59  2 TMDD ® BG 52 1.54 1.54 1.54 1.54  3 Butyl glycol 0.51 0.51 0.51 0.51  4 AMP ®-90 0.10 0.10 0.10 0.10  5 VE-water 11.18 11.18 11.18 11.18  6 Lucenac ® 10MO 7.97 7.33 7.33 7.33  7 Aluminium silicate ASP 600 7.11 6.54 6.54 6.54  8 Titanium rutile 2310 10.41 9.58 9.58 9.58  9 Novacite ® L-207 A 2.07 1.91 1.91 1.91 10 Sillitin ® N 85 3.20 2.95 2.95 2.95 11a iron(III)-tris(N,N-diethyl 2.46 dithiocarbamate) 11b iron(III)-tris(N,N-dimethyl 2.46 dithiocarbamate) 11c iron(III)-tris(N,N-pyrrolidine 2.46 dithiocarbamate) 12 Che ® Coat DF 0682 0.15 0.15 0.15 0.15 13 VE-water 4.62 4.62 4.62 4.62 14 Byk ®-346 0.51 0.51 0.51 0.51 component 2 15 Bisphenol-A-diglycidyl ether. 11.82 11.82 11.82 11.82 M.sub.w < 700 g/mol 16 Butylglycol acetate 3.94 3.94 3.94 3.94 17 water 20.27 20.27 20.27 20.27

(39) The coating compositions E1 to E3 according to the various embodiments herein thus contain an iron(III)-tris(N,N-dithiocarbamate) complex while the comparative coating composition V6 is free of any dithiocarbamates.

(40) The amount of water added in the last step in the preparation of the coating compositions E1 to E3 and V6 serves to control the viscosity.

(41) 4.2 Preparation of Coated Substrates with the Coating Compositions E1 to E3 According to the Various Embodiments Herein and Comparative Coating Composition V6

(42) One of the coating compositions E1 to E3 according to the various embodiments herein or the comparative coating composition V6 is in each case applied as primer coating to a table made of a commercially available aluminium alloy (EN AW 2024, substrate T3 clad, where the clad layer is a plating of purest aluminium) as substrate.

(43) The sheets used in each case have a total surface of about 70 cm.sup.2. Each sheet was pretreated by means of a tartaric acid-sulfuric acid-anodization (TSA) according to DIN EN 4704 (date: May 2012).

(44) On each substrate (T3) is applied on one side one of the coating compositions E1 to E3 according to the various embodiments herein or the comparative coating composition V6 by means of spraying with a spray gun. The dry film thickness in each case is 20-35 μm.

(45) 4.3 Investigation of the Anti-Corrosive Effect of Substrates Coated with the Coating Compositions E1 to E3 According to the Various Embodiments Herein and the Comparative Coating Composition V6

(46) The previously described substrates T3E1, T3E2, T3E3 and T3V6 coated with one of the coating compositions E1 to E3 and V6, respectively, were examined for their corrosion inhibition.

(47) To prepare for the neutral salt spray mist test the thus coated tables were stored 7 days at 15-25° C., after which a cross cut with a width of 1 mm was scored in a depth of 300 μm.

(48) To prepare for the filiform corrosion test the thus coated tables were stored 24 h at 15-25° C., whereupon a top coat layer (D1) was applied in a dry film thickness of 50 to 70 μm to obtain the coated sheets T3E1D1, T3E2D1, T3E3D1 and T3V6D1. For application of the top coat layer in each case the commercial product Glasurit® of series 68 (RAL 9010), a 2K polyurethane-based top coat, was used. The subsequent drying or rather curing took place by means of a storing of the coated sheets for a duration of 7 days at 15-25° C.

(49) The neutral salt spray mist test and the filiform corrosion test were carried out in a test sequence corresponding to the above-indicated determination methods. The results are given in Tables 5 and 6, wherein each value is the average value of a dual determination, standardized to the result of T3V6.

(50) TABLE-US-00005 TABLE 5 Results of the neutral salt spray mist test on 2024-T3-clad substrates coated with one of the coating compositions E1 to E3 according to the various embodiments herein or the comparative coating composition V6. Substrate Penetration in the neutral salt spray mist test, composition after 3,000 h T3V6 1.0 T3E1 0.9 T3E2 1.0 T3E3 0.6

(51) TABLE-US-00006 TABLE 6 Results of the filiform corrosion test on 2024-T3-clad substrates coated with one of the coating compositions E1 to E3 according to the various embodiments herein or the comparative coating composition V6 and a top coat D1. Penetration following the Substrate filiform corrosion test composition 504 h 1,008 h T3V6D1 1.00 1.00 T3E1D1 1.00 0.96 T3E2D1 0.74 0.77 T3E3D1 0.82 0.70

(52) The results of Tables 5 and 6 substantiate the improved anti-corrosive effect of coats prepared from one of the coating compositions E1 to E3 according to the various embodiments herein in comparison with a coat prepared from the comparative coating composition V6 on aluminium substrates (2024-T3 clad).

(53) The neutral salt spray mist test (Table 5) shows that after 3,000 h the penetration of substrates T3E1 to T3E3 coated according to the various embodiments herein was at least comparable or clearly improved in comparison with the substrate T3V6 coated with comparative coating composition V6. The best result in the neutral salt spray mist test was obtained with iron(III)-tris(N,N-pyrrolidine dithiocarbamate).

(54) The penetration as a result of filiform corrosion (Table 6) was likewise clearly improved. Already after 504 h a visible reduction of the penetration of T3E2D1 and T3E3D1 in comparison with T3V6D1 is shown. At a total test duration of 1,008 h all substrates T3E1D1 to T3E3D1 coated according to the various embodiments herein perform clearly better in part following filiform corrosion in comparison with substrate T3V6D1 coated with comparative coating composition V6.

(55) The combination of the results of the two protection-against-corrosion tests of Tables 5 and 6 shows unequivocally that the substrates coated with a coating composition according to the various embodiments herein perform better in at least one of the two tests in comparison with the comparative example. While for example T3E2 after 3,000 h of neutral salt spray mist test shows only a comparable penetration, the penetration as a result of filiform corrosion on T3E2D1 is clearly improved vis-à-vis comparative example T3V6D1.

Example 5.1

Preparation of Coating Compositions E4 to E6 According to the Various Embodiments Herein and Comparative Coating Composition V7

(56) In a further investigation the effect of the weight content of the dithiocarbamate complex on the coating composition, e.g. on iron(III)-tris(N,N-dimethyl dithiocarbamate) was examined. To this end further coating compositions E4 to E6 according to the various embodiments herein and a further comparative coating composition V7 were prepared (Table 7).

(57) The two components of the coating compositions E4 to E6 according to the various embodiments herein and the comparative coating composition V7 were prepared in the following way (Table 7): positions 1-5 were presented and predispersed 15 min, after which positions 6-12, where applicable, were added with stirring. After that, the mixture was dispersed for 30 min at maximum 50° C. to a granularity of less than 20 μm, measured with a Grindometer according to Hegman (ISO 1524), by means of a pearl mill. Positions 13 and 14 of component 1 were stirred in after the dispersion. The ingredients of component 2 were added together in the specified sequence and intimately mixed, after which the two components of the coating composition were mixed shortly before use.

(58) TABLE-US-00007 TABLE 7 Preparation of coating compositions E4-E6 according to the various embodiments herein and comparative coating composition V7. Pos. Ingredient V7 E4 E5 E6 component 1 1 Waterpoxy 751 17.75 17.75 17.75 17.75 2 TMDD BG 52 1.90 1.90 1.90 1.90 3 Butyl glycol 0.63 0.63 0.63 0.63 4 AMP-90 0.13 0.13 0.13 0.13 5 VE-water 13.79 13.79 13.79 13.79 6 Lucenac 10MO 9.83 9.04 8.26 7.47 7 Aluminium silicate ASP 600 8.77 8.07 7.37 6.67 8 Titanium rutile 2310 12.84 11.81 10.79 9.76 9 Novacite L-207 A 2.56 2.36 2.15 1.95 10 Sillitin N 85 3.95 3.63 3.32 3.00 11 iron(III)dimethyl dithiocarbamate 3.04 6.07 9.11 12 Che Coat DF 0682 0.19 0.19 0.19 0.19 13 VE-water 5.69 5.69 5.69 5.69 14 Byk-346 0.63 0.63 0.63 0.63 component 2 15 Bisphenol-A-diglycidylether, 13.34 13.34 13.34 13.34 M.sub.w < 700 g/mol 16 Silquest ® A-187, adhesion 1.86 1.86 1.86 1.86 promoter, Momentive 17 Butyl acetate 5.07 5.07 5.07 5.07 18 water 20.00 20.00 20.00 20.00 19 Butyl glycol 2.75 2.75 2.75 2.75
5.2 Preparation of Coated Substrates with Coating Compositions E4 to E6 According to the Various Embodiments Herein and Comparative Coating Composition V7

(59) One of the coating compositions E4 to E6 according to the various embodiments herein or the comparative coating composition V7 is in each case applied as a primer coating to a table made of a commercially available aluminium alloy (EN AW 2024, substrate T3 clad, where the clad layer is a plating of purest aluminium) as substrate.

(60) The sheets used in each case have a total surface of about 70 cm.sup.2. Each sheet was pretreated by means of a tartaric acid-sulfuric acid-anodization (TSA) according to DIN EN 4704 (date: May 2012).

(61) On each substrate (T3) is applied on one side one of the coating compositions E1 to E3 according to the various embodiments herein or the comparative coating composition V6 by means of spraying with a spray gun. The dry film thickness in each case is 13-30 μm.

(62) 5.3 Investigation of the Anti-Corrosive Effect Substrates Coated with Coating Compositions E4 to E6 According to the Various Embodiments Herein and Comparative Coating Composition V7

(63) The previously described substrates T3E4, T3E5, T3E6 and T3V7 coated with one of the coating compositions E4 to E6 and V7, respectively, were examined for their corrosion inhibition.

(64) To prepare for the neutral salt spray mist test the thus coated tables were stored 7 days at 15-25° C., after which a cross cut with a width of 1 mm was scored in a depth of 300 μm.

(65) To prepare for the filiform corrosion test the thus coated tables were stored 24 h at 15-25° C., whereupon a top coat layer (D1) was applied in a dry film thickness of 50 to 70 μm to obtain the coated sheets T3E4D1, T3E5D1, T3E6D1 and T3V7D1. For application of the top coat layer in each case the commercial product Glasurit® of series 68 (RAL 9010), a 2K polyurethane-based top coat, was used. The subsequent drying or rather curing took place by means of a storing of the coated sheets for a duration of 7 days at 15-25° C.

(66) The neutral salt spray mist test and the filiform corrosion test were carried out in a test sequence corresponding to the above-indicated determination methods. The results are given in Tables 8 and 9, wherein each value is the average value of a dual determination, standardized to the result of T3V7.

(67) TABLE-US-00008 TABLE 8 Results of the neutral salt spray mist test on 2024-T3-clad substrates coated with one of the coating compositions E4 to E6 according to the various embodiments herein or comparative coating composition V7. Substrate composition Penetration, 3,000 h T3V7 1.0 T3E4 0.83 T3E5 0.64 T3E6 0.93

(68) TABLE-US-00009 TABLE 9 Results of the filiform corrosion test on 2024-T3-clad substrates coated with one of the coating compositions E4 to E6 according to the various embodiments herein or comparative coating composition V7 and a top coat D1. Substrate Penetration composition 504 h 1008 h T3V7D1 1.00 1.00 T3E4D1 0.69 1.02 T3E5D1 0.61 0.89 T3E6D1 0.64 0.93

(69) The results from Tables 8 and 9 once again substantiate the clearly improved anti-corrosive effect of coats prepared from coating compositions E4 to E6 according to the various embodiments herein in comparison with a coating prepared from comparative coating composition V7 on aluminium substrates (2024-T3 clad).

(70) In this test series the penetration following the neutral salt spray mist test after 3,000 h (Table 8) of the substrates coated with a coating composition E4 to E6 according to the various embodiments herein is clearly improved in comparison with the substrate coated with comparative coating composition V7. Moreover, it is made clear that a further increase of the weight content of iron(III)-tris(N,N-dimethyl dithiocarbamate) complexes probably will not lead to a further improvement of the anti-corrosive effect.

(71) The penetration as a result of filiform corrosion (Table 9) is comparable or was likewise improved. After 504 h, all examples according to the various embodiments herein exhibit a visible reduction of the penetration in comparison with T3V7D1. At a total test duration of 1,008 h, all substrates T3E4D1 to T3E6D1 coated according to the various embodiments herein following filiform corrosion score the same or better in comparison with the substrate T3V7D1 coated with comparative coating composition V7.

(72) With the tests carried out as an example for the present various embodiments herein it could be shown that a chromium-free coating composition was found which after application on a substrate, in particular an aluminium substrate from the area of aircraft manufacturing, has a surprisingly good or clearly improved anti-corrosive effect in comparison with prior art coatings.

(73) The good anti-corrosive effect of coatings according to the various embodiments herein containing poorly water-soluble dithiocarbamate complexes (B) (E1 to E6) is unexpected inasmuch as coatings containing easily water-soluble dithiocarbamates (V2 to V5), such as described in the prior art, lead to a clearly worse protection against corrosion of coatings (compare Tables 5-6 with Tables 8-9). Coatings containing easily water-soluble dithiocarbamates are actually inferior to coatings which are free of dithiocarbamates (V1, V6, V7) (cf. Tables 2-3).