Method for Coating Metal Surfaces, Substrates Coated in This Way, and Use Thereof

Abstract

The invention relates to a method for coating metal surfaces with an acidic aqueous conversion composition which contains: in total 0.01 to 1 g/l of TiF.sub.6.sup.2+, ZrF.sub.6.sup.2+ and/or HfF.sub.6.sup.2 calculated as ZrF.sub.6.sup.2+, 0 or 0.01 to 1 g/l in each case of Fe.sup.2+, Mn and/or Zn ions, of which at least one type of these ions is present in a content range from 0.01 to 1 g/l, 0 or 0.01 to 2 g/l of organic polymer and/or copolymer, 0 or 0.01 to 2 g/l of ultrafme particulate SiO.sub.2, approximately 0 or 0.01 to 10 g/l of at least one surfactant, approximately 0 or 0.05 to 10 g/l of anions of carbonate, nitrate and/or sulphate, and 0 or 0.001 to 2 g/l of carboxylate and/or sulphonate anions, wherein the content of molybdate and/or of P-containing oxy anions is in each case <0.1 g/l or is approximately 0 g/l, and wherein the composition has a pH value in the range from 2.5 to 6.5. The invention also relates to a corresponding coating and to the use of the substrates coated in this way.

Claims

1-22. (canceled)

23. A method of coating a substrate comprising the steps of: contacting a metallic surface of a substrate with an aqueous acidic conversion composition to produce a coating on the metallic surface, wherein the aqueous acidic conversion composition is a solution or a dispersion comprising: a total content of 0.01 to 1 g/L of TiF.sub.6.sup.2+, ZrF.sub.6.sup.2+ and/or HfF.sub.6.sup.2+ ions, calculated as ZrF.sub.6.sup.2+; 0 or 0.01 to 1 g/L of at least one type of ions selected from the group consisting of Mn and Zn ions; 0 or 0.01 to 2 g/L of an organic polymer and/or an organic copolymer which is stable at a pH of <6.5, based on the solids content; 0 or 0.01 to 2 g/L of particulate SiO.sub.2 with an average particle diameter <0.3 m, based on the solids content; about 0 or 0.01 to 10 g/L of at least one surfactant; about 0 or 0.05 to 10 g/L of anions selected from the group consisting of carbonate, nitrate and sulfate; 0 or 0.001 to 2 g/L of at least of type of anions selected from the group consisting of carboxylate and sulfonate, which cause little or no impairment of the layer-forming process, calculated as the corresponding anions; <0.1 .sub.g/L of at least one component selected from the group consisting of molybdate, calculated as MoO.sub.4.sup.2+, and a P-containing oxyanion, calculated as PO.sub.4.sup.3+; and wherein the aqueous acidic conversion composition has a pH in the range of 2.5 to 6.5.

24. The method according to claim 23, wherein the aqueous acidic conversion composition further comprises: a total content of 0.03 to 5 g/L of lithium, sodium and/or potassium ions; 0 or 0.05 to 5 g/L of ammonium ions; a total content of about. 0 or 0.05 to 0.3 g/L of Co and/or Ni ions; 0 or 0.01 to 0.8 g/L of chlorate, calculated as ClO.sub.3.sup., nitrite, calculated as NO.sub.2 and/or peroxide, calculated as H.sub.2O.sub.2; 0 or 0.01 to 0.5 g/L of free fluoride, calculated as F.sup.; and 0 or 0.01 to 0.2 g/L of vanadate ions, calculated as VO.sub.4.sup.3.

25. The method according to claim 23, wherein the coating has a layer thickness of 0.3 to 3 m.

26. The method according to claim 25, wherein the coating has a total application of elementary zirconium and/or titanium, measured as an element, in a range of 1 to 300 mg/m.sup.2 as measured by X-ray fluorescence analysis.

27. The method according to claim 23, wherein the coating is colored, iridescent or gray.

28. The method according to claim 23, wherein the coating is a replacement for an alkali phosphate coating.

29. The method according to claim 23 further comprising diluting one or two concentrates with water by a dilution factor in a range of 5:1 to 40:1 to prepare the aqueous acidic conversion composition used in the coating step.

30. The method according to claim 23, wherein the step of contacting the metallic surface of the substrate with the aqueous acidic conversion composition occurs for a period of time in a range of 1 second to 10 minutes.

31. The method according to claim 23, wherein the metallic surface is at a temperature in a range of 5 C. to 90 C. when brought into contact with the aqueous acidic conversion composition.

32. The method according to claim 23, wherein the aqueous acidic conversion composition is at a temperature in a range of 35 C. to 70 C., when brought into contact with the metallic surface of the substrate.

33. The method according to claim 23 further comprising cleaning the metallic surface of the substrate before the contacting step.

34. The method according to claim 23, wherein the aqueous acidic conversion composition further comprises at least one surfactant thereby enabling cleaning of the metallic surface of the substrate in the same step as the contacting step.

35. The method according to claim 23 further comprising (i) rinsing the coating with water or with an aqueous after-rinse solution comprising at least one component selected from the group consisting of silane, an organic polymer and an organic copolymer; and (ii) optionally enameling the coating.

36. The method according to claim 23 further comprising (i) drying the coating if the coating does not contain an organic polymer or an organic copolymer; and (ii) optionally enameling the coating without a subsequent rinsing with water or with an aqueous after-rinse solution comprising at least one component selected from the group consisting of silane, an organic polymer and an organic copolymer.

37. The method according to claim 23 wherein, if the coating does contain an organic polymer and/or an organic copolymer, then the coating is not further contacted with a primer, enamel or adhesive.

38. The method according to claim 23 further comprising (i) rinsing the coating with at least one of water and an aqueous after-rinse solution; and (ii) subsequently contacting the coating with at least one component selected from the group consisting of primer, enamel and adhesive.

39. The method according to claim 38, wherein the aqueous after-rinse solution comprises at least one of each: a) cation selected from alkaline earth metal, aluminum, titanium, yttrium and heavy metal cations, b) an organic polymer and/or an organic copolymer, c) silane, silanol, siloxane and/or polysiloxane and/or d) complex fluoride.

40. A method for coating a substrate comprising the steps of: contacting a metallic surface of the substrate with an aqueous acidic conversion composition to produce a coating on the metallic surface; optionally rinsing the coating with water, and/or optionally rinsing with an aqueous composition comprising an organic polymer and/or organic copolymer that is stable at a pH of <6.5, a zirconium complex fluoride and/or silane; and enameling the coating; wherein the aqueous acidic conversion composition is a solution or a dispersion consisting essentially of: a total content of 0.01 to 1 g/L of TiF.sub.6.sup.2+, ZrF.sub.6.sup.2+ and/or HfF.sub.6.sup.2+ ions, or only ZrF.sub.6.sup.2+ ions, calculated as ZrF.sub.6.sup.2+; 0 or 0.01 to 1 g/L of at least one type of ions selected from the group consisting of Mn and Zn ions; 0 or 0.01 to 2 g/L of an organic polymer and/or an organic copolymer which is stable at a pH of <6.5, based on the solids content; optionally 0.01 to 2 g/L of particulate SiO.sub.2 with an average particle diameter <0.3 m, based on the solids content; optionally 0.01 to 10 g/L of at least one surfactant that is essentially phosphate-free and essentially phosphonate-free.

41. A metallic surface of a substrate coated by the method of claim 1.

42. The method according to claim 23, wherein the method is a substitute for an alkali phosphating method or a zinc phosphating method.

Description

EXAMPLES AND COMPARATIVE EXAMPLES

[0113] The subject matter of the invention will now be explained in greater detail on the basis of exemplary embodiments. These examples were carried out using the substrates, process step, substances and mixtures discussed below.

[0114] The following standard sheet metal plates were used: Gardobond C of cold rolled steel, CRS, from St14 DCO5, Gardobond HDG/5 from the corresponding hot-dip galvanized steel or Gardobond F from AA 5005 from AlMg1 from Chemetall GmbH for coating. Unless otherwise indicated, standard Gardobond C plates were used.

[0115] Aqueous conversion compositions corresponding to those listed in Table 1 were prepared using as the surfactant a nonionic surfactant of the Gardobond additive H7438 which ensured an additional cleaning of the metal surface. The alkaline potassium hydroxide-stabilized SiO.sub.2 dispersion Gardobond additive H7157 from Chemetall GmbH had a solids content of 20% and an average particle size of 0.2 m. The polymer dispersion 1 AC 2773, based on acrylate from Alberdingk had a solids content of 53%. The copolymer dispersion 2 VA 294 VP containing acrylate from Alberdingk had a solids content of 47%. The acrylate-containing copolymer dispersion 3 AS 2084 VP from Alberdingk had a solids content of 53%. Copolymer, SiO.sub.2 particles and/or surfactant were added separately to the previously prepared aqueous conversion composition toward the end of the mixing process. In individual experiments ammonium molybdate was added.

[0116] The plates were conversion coated at 55 C. for 3 min utes with a cleaning effect. Then they were rinsed once with process water and then with deionized water before drying the coated plates at 120 C. in a drying cabinet for at least 10 minutes. When using a different temperature, no definite difference in quality was observed.

[0117] Next, one and only one enamel layer was applied to the conversion coated plates. Either an epoxy-polyester powder coating of Interpon 700 from Akzo Nobel Power Coatings GmbH was applied in a layer thickness of 60 to 80 m, or a wet coating of Alexit Monolayer, based on polyurethane and isocyanate from Mankiewicz, was applied in a layer thickness of 60 to 80 m or Cathoguard 350, a black cathodic dip coat from BASF, was applied in a layer thickness of 20 m.

[0118] The enamel adhesion of the enameled samples was determined in the cross-cut method according to DIN EN ISO 2409 before and after 240 hours of alternating climate test. The corrosion resistance of the enameled samples was determined in the salt spray test according to DIN 50021 over 500 hours in the neutral salt spray test NSS in which case a single enamel layer was appliedunlike what is customary in the Asian and North American markets.

[0119] The layer weight was measured in mg/m.sup.2 using X-ray fluorescence analysis for an application of elemental zirconium. The element zirconium is often the indicator element for the quality of the coating, wherein different applications of metal to zirconium were deposited using the same aqueous composition but different metal substrates.

[0120] In the Comparative Examples VB1 and VB2, the examples according to the invention were compared with high quality alkali phosphating, which is widely used internationally on Gardobond C plates made of cold rolled steel: the typical procedure in alkali phosphating, which is also known as iron phosphating, when used on iron and steel materials, was performed using Gardobond WH =Gardobond A 4976 on steel surfaces at 55 C. for 3 minutes, rinsing with deioni zed water and optionally with a subsequent after-rinse for 5 minutes with a Gardolene D 6800 after-rinse based on ZrF.sub.6 before drying for at least 10 minutes in a drying cabinet at 120 C.

TABLE-US-00001 TABLE 1 Overview of the compositions of the aqueous baths and the properties of the respective coated samples and the coatings Content in g/L VB1 VB2 VB3 VB4 VB5 VB6 B1 B2 B3 B4 Iron phosphating GB A 4976 A 4976 Zr as H.sub.2ZrF.sub.6 0.50 1.00 0.05 0.30 0.30 0.30 0.30 0.30 Mn 0.15 0.15 0.15 0.15 Zn 0.15 0.15 0.15 0.15 Surfactant: GBA H7438 4 4 3 3 3 3 3 3 3 3 pH 5.4 5.4 4.8 4.8 4.8 4.8 3.5 4.2 4.8 5.4 After-rinse with yes Gardolene D6800/6 Color of the layer blue blue lightly blue* light light light blue blue yellow purple purple golden golden golden blue purple yellow yellow yellow Layer weight of Zr 0 7 41 77 55 46 79 105 134 81 mg/m.sup.2 Enamel adhesion in the cross-cut test after 240 hours of condensate climate test according DIN EN ISO 2409: In wet paint 60-80 m GT 4 GT 1 GT 0 GT 0 GT 0-1 GT 0 GT 0 GT 0 GT 0 GT 0 In powder coating GT 3 GT 2 GT 0 60-80 m Corrosion resistance in a salt spray test according to DIN 50021 500 h NSS in mm: In wet paint 60-80 m 8.0 3.0 3.0-4.5 2.0-3.0 1.0-2.5 2.0 0.0-2.0 1.0 2.0-2.5 3.0 In powder coating 5.0 2.0 1.0-2.0 60-80 m In cathodic dip coating 1.0-2.0 *unevenly blue Content in g/L B9 B10 B11 B12 B13 B14 B15 VB16 B17 B18 Zr as H.sub.2ZrF.sub.6 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Mn 0.05 0.15 0.50 0.025 0.15 0.50 0.15 Zn 0.05 0.15 0.50 0.025 0.15 0.50 0.15 NH.sub.4 molybdate as MoO.sub.4 0.02 Surfactant: GBA H7438 3 3 3 3 3 3 3 3 3 3 pH 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 Color of the layer light light golden golden golden blue light golden golden golden golden golden yellow to yellow yellow purple golden yellow yellow to yellow to yellow yellow blue yellow blue blue Layer application Zr 44 59 96 55 60 112 46 63 88 112 mg/m.sup.2 Enamel adhesion in the cross-cut test after 240 hours in the condensate climate test according DIN EN ISO 2409: In wet paint 60-80 m GT 0 GT 0 GT 0 GT 0 GT 0 GT 0 GT 0 GT 0 GT 0 GT 0 Corrosion resistance in the salt spray test according to DIN 50021 500 h NSS in mm: In wet paint 60-80 m 2.5 1.0-2.0 2.5 2.0 2.0-2.5 2.5-3.0 2.0 0-3.0 4.0 0-2.5 Content in g/L B19 B20 B21 B22 B23 B24 B25 B26 B27 B28 Zr as H.sub.2ZrF.sub.6 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Ti as H.sub.2TiF.sub.6 0.02 0.20 0.50 Mn 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Zn 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 NH.sub.4 molybdate as MoO.sub.4 0.08 0.33 Polymer dispersion 1 0.10 0.50 1.00 3.00 Copolymer dispersion 2 0.10 Surfactant: GBA H7438 3 3 3 3 3 3 3 3 3 3 pH 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 Color of the layer golden golden golden yellow yellow to yellow to golden golden golden blue to yellow to yellow to yellow to purple blue yellow to yellow to yellow to purple purple purple purple purple purple purple Layer application Zr 76 29 68Zr, 10Ti 1Zr, 18Ti 1Zr, 23Ti 102 98 123 102 126 mg/m.sup.2 Enamel adhesion in the cross-cut test after 240 hours condensate climate test according DIN EN ISO 2409: In wet paint 60-80 m GT 0 GT 0 GT 0 GT 4-5 GT 0 GT 0 GT 0 GT 0 GT 0 GT 0 Corrosion resistance in the salt spray test according to DIN 50021 500 h NSS in mm: In wet paint 60-80 m 2.5 >10 1.0-2.0 1.5 1.0 0.5-1.5 0-0.5 1.5 0 0-1.5 Content in g/L B29 B30 B31 B32 B33 B34 B35 B36 B37 B38 Zr as H.sub.2ZrF.sub.6 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Mn 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Zn 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 SiO.sub.2 nanoparticles 0.20 1.00 5.00 Copolymer dispersion 2 0.50 1.00 3.00 Copolymer dispersion 3 0.10 0.50 1.00 3.00 Surfactant: GBA H7438 3 3 3 3 3 3 3 3 3 3 pH 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 Color of the layer blue to blue to yellow to yellow to yellow to yellow to yellow to purple yellow to golden purple purple purple purple purple purple purple purple yellow Layer application Zr 115 126 99 116 98 104 81 126 102 71 mg/m.sup.2 Enamel adhesion in the cross-cut test after 240 hours condensate climate test according DIN EN ISO 2409: In wet paint 60-80 m GT 0 GT 0 GT 0 GT 0 GT 0 GT 0 GT 0 GT 0 GT 0 GT 0 Corrosion resistance in the salt spray test according to DIN 50021 500 h NSS in mm: In wet paint 60-80 m 0-3.0 0-1.0 0-1.0 0-1.0 1.5 1.5 5.0 0-2.0 0-3.0 0-1.0 Content in g/L B39 B40 B41 B42 B43 Metallic substrate CRS CRS CRS CRS HDG/5 In comparison with example Zr as H.sub.2ZrF.sub.6 0.30 0.30 0.30 0.30 0.30 Mn 0.15 0.15 0 0 0.15 Zn 0.15 0.15 0 0 0.15 Fe.sup.2+ 0.20 ** 0.80 ** NO.sub.2 as NaNO.sub.2 0.10 1.00 Surfactant: GBA H7438 3 3 3 3 3 pH 4.8 4.8 4.9 4.9 4.8 After-rinse with Color of the layer purple invisible blue to blue to yellowish purple purple iridescent Layer application Zr 127 1 101 94 20 mg/m.sup.2 Enamel adhesion in the cross-cut test after 240 hours in the condensate climate test according DIN EN ISO 2409, optionally after an after-rinse at: Wet paint 60-80 m GT 0 GT 3 GT 0 GT 0 GT 0-1 Powder coating 60-80 m GT 0-1 KTL + automotive engineering Corrosion resistance in the salt spray test according to DIN 50021 500 h NSS in mm, optionally after an after-rinse with: Wet paint 60-80 m 0-1.0 4.5 2.5 3.0 Powder coating 60-80 m 2-10 KTL + automotive engineering Content in g/L B44 B45 B46 B47 B48 Metallic substrate AA 5005 CRS CRS CRS CRS In comparison with B3, VB2 B3 B3 B3 example Zr as H.sub.2ZrF.sub.6 0.30 0.30 0.30 0.30 0.30 Mn 0.15 0.15 0.15 0.15 0.15 Zn 0.15 0.15 0.15 0.15 0.15 Fe.sup.2+ NO.sub.2 as NaNO.sub.2 Surfactant: GBA H7438 3 pH 4.8 5.2 5.2 5.2 5.2 After-rinse with Gardolene Gardolene Oxsilan Polymer D6800/6 D6890 9810/3 dispersion 1: 0.1 g/L Color of the layer blue golden golden golden golden iridescent yellow yellow yellow yellow Layer application Zr 50 90 70 70 75 mg/m.sup.2 Enamel adhesion in the cross-cut test after 240 hours in the condensate climate test according DIN EN ISO 2409, optionally after an after-rinse at: Wet paint 60-80 m GT 0 Powder coating 60-80 m GT 0 KTL + automotive GT 0-1 GT 0-1 GT 0 GT 0-1 engineering Corrosion resistance in the salt spray test according to DIN 50021 500 h NSS in mm, optionally after an after-rinse with: Wet paint 60-80 m 0.0-2.0 Powder coating 60-80 m 0 * 1.0-2.0 KTL + automotive 4.0 3.5 2.5 2.5 engineering * same value also at 1000 h in the NSS salt spray test ** amounts added

[0121] These examples illustrate that excellent coatings which have an excellent corrosion resistance, an excellent paint adhesion and usually also a distinct color are obtained by using the aqueous conversion compositions according to the invention. The corrosion resistance on steel surfaces is almost as good as that of the high quality zinc phosphating and is therefore far superior to the corrosion resistance of a high quality alkali phosphating (e.g., B3 in comparison with VB1).

[0122] In the comparative example VB2, the coating properties were determined only after an additional second conversion treatmentunlike the examples according to the invention. The paint adhesion on steel surfaces is almost as good as that with a high quality zinc phosphating and is thus very definitely superior to a high quality alkali phosphating. In addition, the aqueous conversion compositions according to the invention have a very environmentally friendly composition, are advantageous from the standpoint of occupational health and are phosphate-free.

[0123] If an after-rinse solution was used, for example, such as solution with a silane content, an organic polymer content and/or an organic copolymer content after the corrosion conversion coating according to the invention and after at least one rinsing with water, then paint adhesion to steel surfaces achieved in this way is at least as good as that with a high quality zinc phosphating and a corrosion resistance at least as good as that of a high quality zinc phosphating was also achieved.

[0124] On the whole, it has been found that the aqueous acidic conversion compositions according to the invention are excellent for replacement of alkali phosphating on a variety of types of metallic substrate surfaces and not only for iron phosphating on iron and steel surfaces. A multimetal capability in the treatment has even been found so that a mix of different types of metallic surfaces can be treated either simultaneously or in succession in the same bath.

[0125] If ZrF.sub.6 is replaced by TiF.sub.6, there may optionally be a minor impairment in corrosion protection when used on steel in particular. When only zinc was used as the heavy metal cation, high quality coatings were obtained even when the zinc content of the coatings remained unexpectedly extremely low. When using only manganese as the heavy metal cation, high quality coatings were obtained although the manganese content of the coatings was also unexpectedly extremely low. If manganese and zinc were used at the same time, minor impairments were observed in some cases in comparison with the use of only one of these types of heavy metal cations.

[0126] When using only Fe.sup.2+ as a heavy metal cation or in addition to Mn and/or Zn ions, high quality coatings were also obtained. Fe.sup.2+ can be resupplied from the bath of substrate surfaces containing iron through a reaction-induced pickling process. However, the iron is then frequently oxidized to Fe.sup.3+ due to the circulation of the bath and is then withdrawn from the bath as a reactive constituent. Despite the addition of Fe.sup.2+, a steady-state Fe.sup.2+ concentration is often established in the range of 0.025 to 0.1 g/L Fe.sup.2+, as also occurs in Examples B41 and B42.

[0127] In the case of longer-lasting coatings with a plurality of substrates, for example, the main elements and some of the alloying elements are removed by pickling in the aqueous acidic conversion composition and can accumulate in the bath composition to some extent, so in that case there are frequently more cations in the bath at the same time and can have subordinate effects on their properties, in particular affecting the composition of the coating.

[0128] If no heavy metal cations at all were added in Comparative Examples VB3 and VB4, in most cases inferior coatings were obtained. Zn and Mn are deposited only in insignificant immeasurable quantities, based on measurements by X-ray fluorescence analysis, in contrast with Zr. However, Zr is the main component of the layer and may be present as Zr(OH).sub.xF.sub.y, for example. Zn often acts as a fluoride scavenger in the interface between the metal and the coating, so that less fluoride can be incorporated into the layer, which is understood to mean leads to better properties, based on the information available to the present applicant. Zn and Mn are components of the layer only in relatively small amounts and can therefore be detected analytically with some accuracy only by means of photoelectron spectroscopy XPS/ESCA.

[0129] The properties of the coatings to be produced are then the best when the Zr layer is the thickest in comparative tests. However, the Zr layer varies with different grades of steel and also in the case of the same grade of steel with different surface properties.

[0130] In the experiments, a nonionic surfactant that was added further improved the cleanliness of the metallic surface of the standard plates of CRS Gardobond C that were used. The prior cleaning step may therefore be omitted. If the addition of the surfactant was omitted by comparison with the former, the properties of the coating were fundamentally the same but the risk that the metallic surfaces would not be cleaned adequately was increased, and this may also have a negative influence on the properties of a layer.

[0131] In the case of larger amounts of molybdenum added, the possibility of a slight separation of the coating must be considered.

[0132] Addition of an organic polymer, an organic copolymer and SiO.sub.2 nanoparticles have proven to be particularly successful. It should be noted here that when amounts in excess of 0.5 g/L are added, there is no foaming and there are no encrustations on spray nozzles and walls to cause interference.