Method for forming a black passivation layer on a zinc-iron alloy and black passivation composition

Abstract

The present invention refers to a method for forming a black passivation layer on a substrate zinc-iron alloy, to a black passivation composition for depositing a black passivation layer on such an alloy, the composition comprising one or more blackening agents selected from the group consisting of formula (I) and formula (II) as described herein, and to the use of each of said blackening agents for blackening zinc-iron alloys.

Description

[Technical Field]

[0001] The present invention refers to a method for forming a black passivation layer on a zinc-iron alloy and to a black passivation composition for depositing a black passivation layer on such an alloy, the composition comprising one or more blackening agents selected from the group consisting of formula (I) and formula (II) as described herein. [Background technology]

[0002] Various methods are available in the prior art for protecting metal substrates from the effects of corrosive environments. Applying a protective coating / layer of a metal or metal alloy to the metal substrate is a widely used and well-established method. A well-known principle is the deposition of a zinc or zinc-nickel coating / layer on a metal substrate, e.g., an iron metal substrate. Such coatings / layers are often called conversion coatings / layers. Such conversion coatings / layers typically comprise a reaction product (insoluble in aqueous media over a wide pH range) between the metal substrate and the respective conversion treatment solution. To further enhance corrosion resistance, such conversion coatings / layers are further passivated by contacting them with a passivation composition. Such passivation compositions and respective methods are known in the art.

[0003] In addition to zinc and zinc-nickel coatings / layers, other alloys, such as zinc-iron, are becoming more important. Nickel is becoming increasingly suspect in terms of environmental and health issues, and less problematic alternatives are desired.

[0004] In many cases, the passivation composition also changes the color of the conversion coating / layer, for example to a bluish black or even a deep black. In some applications, such color modification is often highly desirable for visual reasons, especially in the automotive field.

[0005] However, for some conversion coatings / layers, the appropriate color modification caused by passivation compositions is either not available at all, results in insufficient color modification, compromises corrosion resistance during color modification, or requires complex passivation compositions that are difficult to handle. This is particularly true for substrates protected with zinc-iron conversion coatings / layers, such as zinc-iron layers. There remains a need to darken them without compromising corrosion resistance.

[0006] EP1816234B1 refers to an aqueous passivating coating composition for zinc or zinc alloys and a method for using the same.

[0007] CN104651823A mentions a cobalt-free, environmentally friendly trivalent chromium black passivation liquid containing tungsten disulfide particles as a blackening agent. CN'823 does not mention zinc-iron alloys.

[0008] WO 97 / 13888 A1 refers to chromate-free corrosion-inhibiting coating compositions that are capable of protecting a wide variety of metal surfaces.

[0009] WO 02 / 49960 A2 refers to certain tripolyphosphates, mixtures thereof and their use as corrosion inhibitors, biocides (antibacterial agents) and, where applicable, encrustation inhibitors.

[0010] EP3360989A1 refers to a method for electrolytically passivating the outermost chromium or chromium alloy layer to increase its corrosion resistance.

[0011] US 2004 / 0170848 A1 mentions that a corrosion-inhibiting composition for coating an article or substrate, such as a metal, a metal coating, a chromate metal coating, etc., contains a film-forming compound, such as a wax or a polymer, and a sulfide salt or a thio compound or a derivative of a thio compound. US '848 does not mention blackening.

[0012] Although black passivation layers have been described in the art, there is a continuing need to improve the blackening of zinc-iron conversion coatings / layers. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] EP1816234B1 [Patent Document 2] CN104651823A [Patent Document 3] WO97 / 13888A1 [Patent Document 4] WO02 / 49960A2 [Patent Document 5] EP3360989A1 [Patent Document 6] US2004 / 0170848A1 Summary of the Invention [Problem to be solved by the invention]

[0014] It was therefore an object of the present invention to provide a method for producing a black passivation layer, in particular on zinc-iron alloys, with improved blackening properties without compromising corrosion resistance. Furthermore, a respective black passivation composition is also needed.

[0015] It is further an object to overcome the above-mentioned drawbacks and to provide a method (together with the respective composition) that is substantially free of particles, thereby making it easy to handle and preventing settling. [Means for solving the problem]

[0016] The object of the above is to provide a method for forming a black passivation layer on a zinc-iron alloy, comprising: (a) providing a substrate comprising the zinc-iron alloy; (b) providing a black passivation composition for depositing the black passivation layer on the zinc-iron alloy, the composition comprising: (i) one or more blackening agents selected from the group consisting of formula (I) and formula (II):

[0017] [ka]

[0018] (In the formula, R 1 and R 2 are independently selected from the group consisting of hydrogen and C1-C5 alkyl; R 3 is selected from the group consisting of sulfonic acids, carboxylic acids, alkylcarboxylic acids, phosphonic acids, salts and esters thereof; n is 1, 2, 3, 4, or 5

[0019] [ka]

[0020] (In the formula, R 4 is selected from the group consisting of sulfonic acids, carboxylic acids, alkylcarboxylic acids, phosphonic acids, salts and esters thereof; m is 1, 2, 3, 4, or 5, and (ii) one or more metal ion species selected from the group consisting of trivalent chromium, titanium, and zirconium; and (c) contacting the substrate with the black passivation composition so that the black passivation layer is formed on the zinc-iron alloy.

[0021] By using one or more of the above blackening agents, very good blackening of zinc-iron alloys can be achieved together with good corrosion resistance. Moreover, the method of the present invention is simple and easy to implement. The inventors' experiments have also shown that the blackening obtained by the method of the present invention and each black passivation composition of the present invention is highly specific to zinc-iron alloys. The inventors' experiments have confirmed that zinc alone and zinc-nickel alloys are not blackened. Further details are provided in the Examples section below.

[0022] The present invention also relates to each of the black passivation compositions described further herein below, and to each of the uses of one or more of the above blackening agents for blackening zinc-iron alloys. Generally, the features described with respect to the method of the present invention, particularly the features described as preferred, apply equally to the black passivation compositions of the present invention, most preferably the black passivation compositions described as preferred, and also apply equally to the uses of the present invention, most preferably the uses described as preferred. DETAILED DESCRIPTION OF THE INVENTION

[0023] In the context of the present invention, the term "trivalent chromium ion" refers to the chromium ion in the oxidation state +3 (also called trivalent chromium ion), including both the free and complex forms. This also applies mutatis mutandis to the metal ions of titanium and zirconium, respectively.

[0024] In the context of the present invention, the term "black passivation layer" also means a black conversion layer.

[0025] Base material Preferably, the black passivation layer has a darkness value L based on the definition of the CIELAB color space. * is 40 or less, preferably 33 or less, and most preferably 25 or less.

[0026] As mentioned above, the method of the present invention is highly specific to zinc-iron alloys. In the zinc-iron alloy, the amount of iron is preferably in the range of 0.1% by mass to 30% by mass, preferably 0.6% by mass to 28% by mass, more preferably 2.1% by mass to 25% by mass, even more preferably 3.5% by mass to 22% by mass, most preferably 4.9% by mass to 18% by mass, and even most preferably 6.1% by mass to 15% by mass, based on the total mass of the zinc-iron alloy. A highly preferred amount of iron is in the range of 4.9% by mass to 30% by mass. Within this highly preferred range, excellent blackening can be easily achieved.

[0027] The method of the present invention is typically applied to zinc-iron alloys. In a preferred embodiment, the zinc-iron alloy is present on a substrate as a layer, preferably as a layer resulting from a galvanizing process, and most preferably as a layer resulting from a zinc-iron plating process. Therefore, in a most preferred embodiment, the zinc-iron alloy is distinguishable from the rest of the substrate. In such a method, the substrate is typically protected from corrosion.

[0028] The method of the present invention is preferred, wherein the substrate contains iron. This means that the substrate preferably comprises a matrix, preferably an iron matrix, more preferably steel, onto which the zinc-iron alloy has been deposited. The zinc-iron alloy is therefore distinguishable from the rest of the substrate (i.e., represented by the matrix).

[0029] However, in some cases, it is preferred that the substrate contains the zinc-iron alloy in the sense that the substrate itself consists of the zinc-iron alloy, in other words, preferably the base material is already the zinc-iron alloy and therefore the base material is the substrate.

[0030] Preferred is a method of the present invention wherein said substrate is a metal or metal alloy substrate, preferably said substrate contains iron, most preferably said substrate contains iron and is different from said zinc-iron alloy.

[0031] Preferred is the method of the present invention wherein the substrate is a workpiece requiring resistance to anodic corrosion, most preferably resistance required for environmentally induced corrosion.

[0032] Typically, preferred substrates are selected from the group consisting of screws, bolts, nuts, and automotive parts.

[0033] The method of the present invention is preferred, wherein one or more substrates are provided in step (a), preferably a plurality of substrates are provided in step (a), this applies in particular when said substrates refer to screws, bolts and nuts.

[0034] The method of the present invention is preferred in which the substrate (preferably a plurality of said substrates) is provided in a barrel or fixed on a rack, and therefore the method of the present invention is applicable to both types.

[0035] Black passivation composition In the method of the present invention, a black passivation composition is used, preferably the black passivation composition of the present invention (see further herein below).

[0036] Preferably, the black passivation composition is also referred to as a conversion composition.

[0037] The method of the present invention is preferred, wherein the black passivation composition is aqueous (i.e., contains water), preferably with a concentration of water greater than 50% by volume, more preferably 75% by volume or more, and most preferably 90% by volume or more, based on the total volume of the black passivation composition. Highly preferably, water is the only solvent.

[0038] Preferably, the black passivation composition is a solution.Thus, a method of the present invention is preferred, wherein the black passivation composition is substantially free, preferably free, of particles (including colloids).

[0039] The method of the present invention is preferred, wherein said black passivation composition is acidic and preferably has a pH of 1.0 to 4.5, preferably 1.2 to 4.0, more preferably 1.4 to 3.3, even more preferably 1.5 to 2.8, most preferably 1.6 to 2.2.

[0040] As mentioned above, the black passivation composition comprises one or more blackening agents as defined above.

[0041] As shown by formula (I) and formula (II), the one or more blackening agents used in the black passivation composition are organic blackening agents. In the method of the present invention, the black passivation composition is preferably substantially free of inorganic blackening agents, preferably free of inorganic blackening agents. Inorganic blackening agents are disclosed, for example, in CN104651823A.

[0042] The method of the present invention is preferred, wherein the black passivation composition comprises at least one or more (preferably one) blackening agent of formula (I). According to the inventors' experiments, the blackening agent of formula (I) provides excellent results (see the examples below).

[0043] Only in some cases is the method of the present invention preferred, in which the black passivation composition is substantially free of, and preferably free of, the blackening agent of formula (II), which is most preferably applied when the black passivation composition already contains the blackening agent of formula (I).

[0044] Generally, the method of the present invention is preferred in which, in the black passivation composition, the one or more blackening agents selected from the group consisting of formula (I) and formula (II) are the only blackening agents in the black passivation composition.

[0045] The method of the present invention is preferred, wherein the total concentration of the one or more blackening agents in the black passivation composition is in the range of 0.2 mmol / L to 100 mmol / L, preferably 0.3 mmol / L to 80 mmol / L, more preferably 0.4 mmol / L to 60 mmol / L, even more preferably 0.8 mmol / L to 45 mmol / L, and most preferably 1.6 mmol / L to 38 mmol / L, based on the total volume of the black passivation composition.

[0046] In particular, the method of the present invention is preferred, in which the black passivation composition contains one or more (preferably one) blackening agents of formula (I) in a total concentration ranging from 0.4 mmol / L to 25.0 mmol / L, preferably 0.6 mmol / L to 20.0 mmol / L, more preferably 0.8 mmol / L to 12.0 mmol / L, even more preferably 1.0 mmol / L to 10.0 mmol / L, and most preferably 1.2 mmol / L to 8.0 mmol / L, based on the total volume of the black passivation composition. Most preferably, in conjunction with such total concentration, the compound of formula (I) is the only blackening agent in the black passivation composition used in the method of the present invention. Surprisingly, excellent blackening was obtained even at relatively low total concentrations of the compound of formula (I), including a total concentration of 0.4 mmol / L. It is highly desirable to maintain a relatively low concentration of the blackening agent so that the shelf life of each black passivation composition is as long as possible. A highly preferred total concentration is in the range of 0.4 mmol / L to 8.0 mmol / L.

[0047] R 1 and R 2 is independently selected from branched and unbranched C1-C5 alkyl, preferably unbranched C1-C5 alkyl.

[0048] R 3 and R 4 The method of the present invention is preferred, wherein said salts are independently selected from the group consisting of ammonium salts and alkali salts, preferably from the group consisting of ammonium, sodium, and potassium.

[0049] R 1 and R 2 are independently selected from the group consisting of hydrogen, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, and tert-butyl, preferably from the group consisting of hydrogen, methyl, ethyl, 1-propyl, and 2-propyl, most preferably from the group consisting of hydrogen and methyl.

[0050] R 1 and R 2 is an alkyl group, preferably one of those listed as preferred above.

[0051] The process according to the invention, wherein n is 2, 3 or 4, preferably 3, is preferred.

[0052] In the method of the present invention, R 3 is selected from the group consisting of sulfonic acids, carboxylic acids, alkylcarboxylic acids, phosphonic acids, salts and esters thereof.

[0053] Sulfonic acid preferably means ~SO3H, where "~" represents a covalent bond connecting this group to another part of the compound of formula (I) above. Carboxylic acid preferably means ~COOH, where "~" represents a covalent bond connecting this group to another part of the compound of formula (I) above. Alkylcarboxylic acid preferably means a saturated branched or unbranched alkyl having one or more (preferably two) carboxylic acid groups, more preferably a saturated branched or unbranched C1-C6 alkyl (preferably C2-C4 alkyl) having one or more (preferably two) carboxylic acid groups, and even more preferably an alkylcarboxylic acid is ~C(COOH)(CH2). kCOOH, where "~" represents a covalent bond connecting this group to other parts of the compound of formula (I) above, and k is an integer from 1 to 5, and most preferably, the alkyl carboxylic acid comprises ~C(COOH)CH2COOH. Phosphonic acid preferably means ~PO3H2, where "~" represents a covalent bond connecting this group to other parts of the compound of formula (I) above. Preferably, R 3 The above description of R in formula (II) 4 shall apply mutatis mutandis.

[0054] R 3 contains at least sulfonic acid, its salts and / or esters, preferably R 3 Preference is given to the process of the present invention, wherein n is 3 and n comprises at least a sulfonic acid, a salt and / or an ester thereof.

[0055] R 3 is selected from the group consisting of sulfonic acids, carboxylic acids, phosphonic acids, and salts thereof, most preferably R 3 contains at least a sulfonic acid and / or a salt thereof, and preferably R 3 More preferred is the method of the present invention, wherein n is 3 and n is at least a sulfonic acid and / or a salt thereof.

[0056] Most preferred is the process of the present invention, wherein formula (I) comprises the compound 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonic acid, its salts and / or esters, preferably 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonic acid and / or its salts.

[0057] A process according to the invention, wherein m is 2, 3 or 4, preferably 3, is preferred.

[0058] R 4 contains at least sulfonic acid, its salts and / or esters, preferably R 4 Preference is given to the process according to the invention, wherein m is 3 and n is at least a sulfonic acid, its salts and / or esters.

[0059] R 4is selected from the group consisting of sulfonic acids, carboxylic acids, phosphonic acids, and salts thereof, most preferably R 4 contains at least a sulfonic acid and / or a salt thereof, and preferably R 4 More preferred is the process of the present invention, wherein comprises at least a sulfonic acid and / or a salt thereof and m is 3.

[0060] Most preferred is the process of the present invention wherein formula (II) comprises the compound 3-(2-benzothiazolylthio)-1-propanesulfonic acid, its salts and / or esters, preferably 3-(2-benzothiazolylthio)-1-propanesulfonic acid and / or its salts.

[0061] The black passivation composition used in the method of the present invention contains one or more metal ion species selected from the group consisting of trivalent chromium, titanium, and zirconium. Although significant darkening of zinc-iron alloys can already be observed without the presence of these metal ions (i.e., in the complete absence of these and other transition metal ions), the metal ions are particularly beneficial for obtaining significant corrosion resistance in addition to the darkening effect. While some corrosion resistance may be present, the corrosion resistance can be significantly further enhanced thereby.

[0062] Preferred is a method of the present invention wherein said one or more metal ion species are selected from the group consisting of trivalent chromium and titanium.

[0063] More preferred is a method of the present invention wherein the one or more metal ion species comprises at least trivalent chromium, and most preferably the one or more metal ion species is trivalent chromium. Experiments by the inventors have shown that trivalent chromium ions have produced superior corrosion resistance results.

[0064] In the method of the present invention, the trivalent chromium metal ions are preferably derived from organic and / or inorganic trivalent chromium ion sources, preferably inorganic trivalent chromium ion sources. Highly preferred trivalent chromium ion sources are organic and / or inorganic trivalent chromium ion sources. A preferred organic trivalent chromium ion source is trivalent chromium citrate. A preferred inorganic trivalent chromium ion source is trivalent chromium chloride hexahydrate.

[0065] In a preferred embodiment of the present invention, the total concentration of the one or more metal ion species is in the range of 0.1 g / L to 30 g / L, preferably 0.2 g / L to 20 g / L, more preferably 0.5 g / L to 14 g / L, even more preferably 0.8 g / L to 10 g / L, and most preferably 1.3 g / L to 6.0 g / L, based on the total volume of the black passivation composition and based on the free ion mass. A highly preferred total concentration is in the range of 0.1 g / L to 4.0 g / L. If the total concentration is significantly below 0.1 g / L, the particularly desirable corrosion resistance is often not achieved. In contrast, if the total concentration is significantly above 30 g / L, no additional benefit is obtained and the cost is typically unacceptable.

[0066] Since trivalent chromium ions are preferred, the method of the present invention is preferred in which the total concentration of the trivalent chromium metal ions is in the range of 0.1 g / L to 8.0 g / L, preferably 0.2 g / L to 7.1 g / L, more preferably 0.5 g / L to 6.1 g / L, even more preferably 0.8 g / L to 5.0 g / L, and most preferably 1.0 g / L to 3.5 g / L, based on the total volume of the black passivation composition. Most preferably, the total concentration of the trivalent chromium metal ions mentioned above is applied with the proviso that these ions are the only type of transition metal in the black passivation composition.

[0067] Below, we will list a number of compounds and ions that are preferably not included in the black passivation composition used in the method of the present invention. Such compounds / ions are either not useful for solving the objectives described in the summary above or even have harmful effects, and are therefore avoided. In some cases, the presence of additional compounds / ions is unavoidable when using the black passivation composition. Usually, it is preferable to use a relatively simple black passivation composition.

[0068] The method of the present invention is preferred in that the black passivation composition is substantially free of, and preferably free of, hexavalent chromium. This includes any compounds and ions containing chromium in the (+VI) oxidation state. It is an important objective of the method of the present invention to avoid any use of hexavalent chromium due to its environmental and health concerns.

[0069] The method of the present invention is preferred in which the black passivation composition is substantially free of thioglycolic acid and its salts, preferably free of thioglycolic acid and its salts. However, the method of the present invention may also be preferred in which the black passivation composition contains thioglycolic acid and / or its salts in addition to one or more blackening agents selected from the group consisting of formula (I) and formula (II) defined above. Experiments by the inventors (data not shown) have shown that the mere presence of thioglycolic acid and / or its salts also often causes significant blackening, although the results obtained are inferior to those obtained with the blackening agents of formula (I) and formula (II) above.

[0070] Preferred is a method of the present invention wherein said black passivation composition is substantially free of nickel ions, preferably free of nickel ions, preferably substantially free of nickel, preferably free of nickel.

[0071] The method of the present invention is preferred in which the black passivation composition is substantially free of intentionally added zinc ions, preferably free of intentionally added zinc ions. If zinc ions are present in the black passivation composition, they are released / dissolved from the zinc-iron alloy during use of the black passivation composition. Therefore, the method of the present invention is preferred in which, if zinc ions are present in the black passivation composition, they are released from the zinc-iron alloy. In other words, if zinc ions are present, their source is the zinc-iron alloy. After preparation of each black passivation composition, zinc ions are typically absent. After initiation of the method of the present invention, the total concentration is very low. As the black passivation composition is used, the total concentration typically increases. Therefore, preferably, after step (c) is performed multiple times, zinc ions are present at a total concentration of 10 g / L or less, preferably 8 g / L or less, and most preferably 5 g / L or less, based on the total volume of the black passivation composition.

[0072] Preferred is the method of the present invention, wherein said black passivation composition is substantially free of silver ions, preferably free of silver ions, preferably substantially free of silver, preferably free of silver.

[0073] Preferred is a method of the present invention wherein said black passivation composition is substantially free of nicotinic acid and its salts, preferably free of nicotinic acid and its salts.

[0074] Preferred is a method of the present invention wherein said black passivation composition is substantially free of phytic acid and its salts, preferably free of phytic acid and its salts.

[0075] In many cases, the method of the present invention is preferred in that the black passivation composition is substantially free of intentionally added disulfides, preferably free of intentionally added disulfides. This preferably means that the black passivation composition is substantially free of, preferably free of, intentionally added ionic disulfides and compounds containing covalent disulfides. Then, only in very rare cases is the method of the present invention preferred in that the black passivation composition contains disulfides, preferably ionic disulfides and / or compounds containing covalent disulfides. However, in general, the absence of such compounds is usually preferred.

[0076] In a preferred embodiment of the present invention, the black passivation composition is substantially free of intentionally added iron ions, preferably free of intentionally added iron ions. If iron ions are present in the black passivation composition, they are released / dissolved from the zinc-iron alloy during use of the black passivation composition. After preparation of each black passivation composition, iron ions are typically absent. After initiation of the present invention, the total concentration is very low. As the black passivation composition is used, the total concentration typically increases. Therefore, preferably, after step (c) is performed multiple times, iron ions are present at a total concentration of 1 g / L or less, preferably 0.8 g / L or less, and most preferably 0.5 g / L or less, based on the total volume of the black passivation composition.

[0077] Preferred is the method of the present invention, wherein said black passivation composition is substantially free of tungsten ions, preferably free of tungsten ions.

[0078] More preferred is the method of the present invention, wherein said black passivation composition is substantially free of tungsten, preferably free of tungsten.

[0079] More preferred is a method of the present invention wherein said black passivation composition is substantially free of tungsten disulfide particles, preferably free of tungsten disulfide particles, preferably substantially free of tungsten disulfide, preferably free of tungsten disulfide.

[0080] Preferred is a method of the present invention wherein said black passivation composition is substantially free of thiodiglycol, preferably free of thiodiglycol.

[0081] The method of the present invention is preferred in that the black passivation composition is substantially free of, and preferably free of, silicon dioxide, silicates, silanes, and silane-containing compounds. Only in very rare cases is the method of the present invention preferred in that the black passivation composition contains silanes and / or silane-containing compounds. It is suspected that the presence of silanes and / or silane-containing compounds may have a positive effect on the corrosion resistance of the black passivation layer. However, in many cases, excellent corrosion resistance is already achieved without the presence of silanes and / or silane-containing compounds.

[0082] More preferred are methods of the present invention in which the black passivation composition is substantially free of cobalt ions, preferably free of cobalt ions, preferably substantially free of cobalt, preferably free of cobalt. The presence of cobalt is becoming an increasing environmental concern. Only in very rare cases are methods of the present invention preferred in which the black passivation composition contains cobalt ions and / or cobalt-containing compounds. The presence of cobalt typically enhances the corrosion resistance of heat-treated substrates having a black passivation layer obtained by the methods of the present invention.

[0083] The black passivation composition comprises: (iii) one or more halide ion species; and / or (iv) one or more carboxylic acids and / or salts thereof Preferably, the method of the present invention further comprises:

[0084] The halide ion is typically a counterion to one or more of the metal ion species selected from the group consisting of trivalent chromium, titanium, and zirconium.

[0085] The method of the present invention is preferred, wherein the total concentration of the one or more halide ion species is in the range of 1 g / L to 18 g / L, preferably 2 g / L to 15 g / L, even more preferably 3 g / L to 12 g / L, most preferably 4 g / L to 10 g / L, and even most preferably 6 g / L to 9 g / L, based on the total volume of the black passivation composition.

[0086] The method of the present invention is preferred, wherein the one or more halide ion species include chloride ions and / or fluoride ions. Most preferably, when the one or more metal ion species are selected from the group consisting of titanium and zirconium, fluoride may also preferably act as a complexing agent for the metal ions. Bromide ions are preferably not included in the black passivation composition.

[0087] More preferably, the total concentration of the chloride ions is 1 g / L to 18 g / L, preferably 2 g / L to 15 g / L, even more preferably 3 g / L to 12 g / L, most preferably 4 g / L to 10 g / L, and even most preferably 6 g / L to 9 g / L, based on the total volume of the black passivation composition. Most preferably, chloride ions are the only type of halogen ions in the black passivation composition.

[0088] The one or more carboxylic acids and / or salts thereof typically act as complexing agents for the one or more metal ion species selected from the group consisting of trivalent chromium, titanium, and zirconium, most preferably trivalent chromium metal ions.

[0089] Preferred is a method of the present invention wherein the one or more of said compounds comprises a dicarboxylic acid, a tricarboxylic acid, and / or a salt thereof.

[0090] Preferred dicarboxylic acids and / or salts thereof include C2 to C6 dicarboxylic acids and / or salts thereof, preferably oxalic acid, malonic acid, and / or salts thereof, most preferably oxalic acid and / or salts thereof.

[0091] Preferred tricarboxylic acids and / or salts thereof include citric acid and / or salts thereof.

[0092] The method of the present invention is preferred, wherein the total concentration of the one or more carboxylic acids and salts thereof is 0.5 mmol / L to 120 mmol / L, preferably 8 mmol / L to 105 mmol / L, even more preferably 15 mmol / L to 90 mmol / L, most preferably 30 mmol / L to 80 mmol / L, and even most preferably 45 mmol / L to 70 mmol / L, based on the total volume of the black passivation composition. More preferably, the total concentration is applied with the proviso that the black passivation composition contains at least one or more dicarboxylic acids and / or salts thereof.

[0093] Even more preferably, the total concentration of the oxalic acid and its salts is 0.5 mmol / L to 120 mmol / L, preferably 8 mmol / L to 105 mmol / L, even more preferably 15 mmol / L to 90 mmol / L, most preferably 30 mmol / L to 80 mmol / L, and even most preferably 45 mmol / L to 70 mmol / L, based on the total volume of the black passivation composition. Most preferably, oxalic acid and its salts are the only dicarboxylic acid and its salts in the black passivation composition, and preferably the only carboxylic acid and its salts in the black passivation composition.

[0094] In some preferred embodiments, the black passivation composition comprises citric acid and / or its salts at a total concentration of 0.5 mmol / L to 120 mmol / L, preferably 8 mmol / L to 105 mmol / L, even more preferably 15 mmol / L to 90 mmol / L, most preferably 30 mmol / L to 80 mmol / L, and even most preferably 45 mmol / L to 70 mmol / L, based on the total volume of the black passivation composition. In such cases, citric acid and its salts are preferably the only tricarboxylic acid and its salt in the black passivation composition, and most preferably the only carboxylic acid and its salt in the black passivation composition.

[0095] The black passivation composition (v) nitrate ion Preferably, the method of the present invention further comprises:

[0096] Nitrate ions preferably act as an oxidizing agent in the black passivation composition.

[0097] The method of the present invention is preferred, wherein the total concentration of the nitrate ions is in the range of 0.1 g / L to 20 g / L, preferably 0.4 g / L to 15 g / L, even more preferably 0.8 g / L to 11 g / L, most preferably 1.2 g / L to 7 g / L, and even most preferably 1.7 g / L to 4.5 g / L, based on the total volume of the black passivation composition.

[0098] Contact with black passivation composition (step (c)) In step (c), the substrate is contacted with the black passivation composition, preferably as described above, more preferably as described above.

[0099] In step (c), the method of the present invention is preferred, wherein the black passivation composition has a temperature in the range of 10°C to 80°C, preferably 15°C to 65°C, even more preferably 19°C to 45°C, and most preferably 22°C to 38°C. If the temperature significantly exceeds 80°C, undesirable rapid dissolution (exfoliation) of the zinc-iron alloy is often observed, impairing corrosion resistance. However, if the temperature is too low, the contact in step (c) often becomes unnecessarily long.

[0100] In step (c), the method of the present invention is preferably carried out for a time period of 10 to 200 seconds, preferably 20 to 160 seconds, even more preferably 40 to 130 seconds, and most preferably 60 to 100 seconds. If the time period significantly exceeds 200 seconds, undesirable rapid dissolution (flaking) of the zinc-iron alloy is often observed, impairing corrosion resistance. However, if the time period is too short, insufficient blackening typically occurs, thereby deteriorating and impairing the visual appearance.

[0101] A preferred method of the present invention is that step (c) is carried out without applying an electric current. Preferably, in step (c) the substrate is immersed in the black passivation composition.

[0102] Post-processing As will be shown in the examples below, if the substrate is further treated after step (c) to enhance its corrosion resistance, very good corrosion resistance is indeed obtained.

[0103] Generally, the method of the present invention is preferred, wherein the substrate obtained after step (c) of the method of the present invention is further treated with a post-dip composition and / or a sealing composition, preferably either in this order or in the reverse order as summarized below.

[0104] Preferably, the process of the present invention is carried out after step (c) in which step (d) is carried out of contacting the substrate obtained after step (c) with a post-dip composition so as to obtain a post-dipped substrate.

[0105] The method of the present invention is preferred, wherein the post-dip composition is acidic, preferably having a pH in the range of 3.0 to 6.8, more preferably 3.5 to 6.5, even more preferably 4.0 to 6.3, most preferably 4.3 to 6.0.

[0106] Preferred is the method of the present invention wherein the post-dip composition contains trivalent chromium ions.

[0107] Preferred is a method of the present invention wherein said sealing composition is substantially free of hexavalent chromium containing compounds and ions, preferably free of hexavalent chromium containing compounds and ions.

[0108] Preferred is the method of the present invention wherein the post-dip composition contains phosphate ions.

[0109] Preferred is a method of the present invention wherein the post-dip composition contains one or more wetting agents.

[0110] Preferred is the method of the present invention, wherein the post-dip composition contains one or more complexing agents, preferably for trivalent chromium ions.

[0111] The method of the present invention is preferred, wherein in step (d) said post-dip composition has a temperature in the range of 18°C ​​to 60°C, preferably 20°C to 58°C, more preferably 28°C to 56°C, even more preferably 33°C to 54°C, and most preferably 38°C to 50°C.

[0112] The method of the present invention is preferred, wherein in step (d) said contacting is carried out for a time period of 5 seconds to 200 seconds, preferably 10 seconds to 140 seconds, even more preferably 20 seconds to 100 seconds, most preferably 30 seconds to 70 seconds.

[0113] Preferably, after step (d) the method of the present invention is carried out in a step (e) of contacting the substrate obtained after step (d) with a sealing composition so as to obtain a sealed substrate.

[0114] The method of the present invention is preferred, wherein said sealing composition is alkaline, preferably having a pH of 9 or more, more preferably 9.1 to 12, even more preferably 9.3 to 11, most preferably in the range of 9.5 to 10.5.

[0115] A method according to the invention is preferred, wherein said sealing composition contains two or more organic compounds.

[0116] Preferred is a method of the present invention wherein said sealing composition is substantially free of trivalent chromium ions, preferably free of trivalent chromium.

[0117] Preferred is a method according to the invention, wherein said sealing composition comprises at least one organic polymer, preferably comprising polyurethane, polyalkylene (preferably polyethylene), polyfluoroalkylene (preferably polytetrafluoroethylene) and / or polyacrylate.

[0118] A method according to the invention is preferred, wherein said sealing composition contains one or more waxes.

[0119] The method of the present invention is preferred, wherein the sealing composition contains one or more silicon-containing compounds, preferably at least one silane and / or at least one inorganic silicate. Preferably, the at least one inorganic silicate is a colloid.

[0120] The method of the present invention is preferred, wherein in step (e), the sealing composition has a temperature in the range of 15°C to 35°C, preferably 17°C to 30°C, more preferably 19°C to 27°C, and most preferably 21°C to 25°C.

[0121] The method of the present invention is preferred, wherein in step (e), the contacting is carried out for a time period of 5 seconds to 200 seconds, preferably 10 seconds to 140 seconds, even more preferably 20 seconds to 100 seconds, and most preferably 30 seconds to 70 seconds.

[0122] When steps (d) and (e) are carried out in this order as summarized above, not only is a very good black passivation layer obtained, but excellent corrosion resistance, most preferably up to 480 hours, and the 5% white rust limit according to ISO 9227, is also obtained.

[0123] Preferred is a method according to the invention, wherein step (e) is followed by a step (f) of drying the substrate obtained after step (e).

[0124] Preferred is a process according to the invention, wherein step (f) is carried out at a temperature in the range of 55°C to 95°C, preferably 58°C to 90°C, more preferably 58°C to 85°C, most preferably 60°C to 80°C.

[0125] Preferred is a method according to the invention, wherein step (f) is carried out for a time period of 2 minutes to 20 minutes, preferably 3 minutes to 16 minutes, even more preferably 4 minutes to 13 minutes, most preferably 6 minutes to 10 minutes.

[0126] Preferably, a drying step, preferably the drying step described above, is also carried out after one or more previous steps, for example after step (c), after step (d), etc. Highly preferred is the method of the present invention, wherein a drying step, preferably a drying step defined in step (f), is carried out after step (d) and before step (e). This is highly preferred since in step (d) the post-dip composition is acidic and in step (e) the sealing composition is alkaline.

[0127] The present invention further provides a black passivation composition for depositing a black passivation layer on a zinc-iron alloy, the composition comprising: (i) one or more blackening agents selected from the group consisting of formula (I) and formula (II):

[0128] [ka]

[0129] (In the formula, R 1 and R 2are independently selected from the group consisting of hydrogen and C1-C5 alkyl; R 3 is selected from the group consisting of sulfonic acids, carboxylic acids, alkylcarboxylic acids, phosphonic acids, salts and esters thereof; n is 1, 2, 3, 4, or 5

[0130] [ka]

[0131] (In the formula, R 4 is selected from the group consisting of sulfonic acids, carboxylic acids, alkylcarboxylic acids, phosphonic acids, salts and esters thereof; m is 1, 2, 3, 4, or 5, and (ii) one or more metal ion species selected from the group consisting of trivalent chromium, titanium, and zirconium; Including, However, reference is also made to black passivation compositions, provided that they are substantially free, and preferably free, of nickel ions, cobalt ions, and tungsten ions.

[0132] In particular, the black passivation composition of the present invention is preferred, wherein said black passivation composition is substantially free of intentionally added zinc ions, preferably free of intentionally added zinc ions. Most preferably, the above remarks regarding zinc ions equally apply to the black passivation composition of the present invention, especially in view of the method of the present invention.

[0133] Preferably, the above-mentioned points regarding the black passivation composition used in the method of the present invention (especially those described as being preferred) also apply to the black passivation composition of the present invention, and this applies in particular to compounds and ions not included in the black passivation composition used in the method of the present invention.

[0134] The present invention further relates to the use of one or more blackening agents selected from the group consisting of formula (I) and formula (II) for blackening zinc-iron alloys.

[0135] [ka]

[0136] (In the formula, R 1 and R 2 are independently selected from the group consisting of hydrogen and C1-C5 alkyl; R 3 is selected from the group consisting of sulfonic acids, carboxylic acids, alkylcarboxylic acids, phosphonic acids, salts and esters thereof; n is 1, 2, 3, 4, or 5

[0137] [ka]

[0138] (In the formula, R 4 is selected from the group consisting of sulfonic acids, carboxylic acids, alkylcarboxylic acids, phosphonic acids, salts and esters thereof; m is 1, 2, 3, 4, or 5 Also mentioned is:

[0139] Preferably, the remarks made above regarding one or more blackening agents of formula (I) and formula (II) used in the black passivation composition used in the method of the present invention (especially those described as preferred) apply equally to the use of the present invention.

[0140] The present invention is described in more detail by the following non-limiting examples. [Example]

[0141] In the examples, various test passivation compositions were prepared and numbered as shown in Table 1 below. Each composition was aqueous and typically contained a metal ion species, 6 g / L to 8 g / L of chloride ion when chromium ion was used, 50 mmol / L to 70 mmol / L of oxalic acid when chromium ion was used or 10 mmol / L to 300 mmol / L of fluoride ion when titanium ion or zirconium ion was used, respectively, as a complexing agent, approximately 1 g / L to 7 g / L of nitrate ion, and one of the following compounds, abbreviated as follows:

[0142] DPS: 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonic acid sodium salt, also known as Raluplate DPS (CAS 18880-36-9, Raschig), R 1 and R 2 is methyl and R 3 is the sodium salt of a sulfonic acid and n is 3

[0143] ZPS: 3-(2-benzothiazolylthio)-1-propanesulfonic acid sodium salt, also known as Raluplate ZPS (CAS 49625-94-7, Raschig), R 4 is the sodium salt of a sulfonic acid and m is 3

[0144] SPS: Bis-(3-sulfopropyl)-disulfide disodium salt, also known as Raluplate SPS (CAS 27206-35-5, Raschig), for comparison

[0145] SPV: 1-(3-sulfopropyl)-2-vinylpyridinium betaine, also known as Raluplate SPV (CAS 90552-35-5, Raschig), for comparison

[0146] MPS: 3-mercaptopropanesulfonic acid sodium salt, also known as Raluplate MPS (CAS 17636-10-1, Raschig), for comparison

[0147] DTO: Dithiooxamide, for comparison

[0148] The specific compounds and their respective total concentrations are summarized below in Table 1. Each test passivation composition has a pH of about 2.

[0149] In each example, a number of u-shaped steel plate samples (base material) as substrates, galvanized with a silvery zinc-iron layer (Hiron-Zn / Fe with a high iron content and Protedur Plus with a low iron content, both manufactured by Atotech, see Table 1 below for iron content) were immersed for about 90 seconds in each test passivation composition at a temperature of about 22° C. In the examples according to the invention, blackening was immediately observed.

[0150] The treated samples were then dried and subjected to a post-dip composition (acidic, containing trivalent chromium phosphate) and a sealing composition (alkaline, containing wax and silicon-containing compounds).The blackening properties were then visually evaluated, and the corrosion resistance was assessed according to ISO 9227.

[0151] [Table 1]

[0152] All of the examples according to the present invention (i.e., Examples I-1, I-2, I-3, I-4, and II-1) resulted in blackening of zinc-iron alloys. Examples I-3 and I-4 gave very good results, and Example I-4 gave such good results over a relatively wide range of concentrations of DPS and chromium ions.

[0153] In contrast, the alternative compounds (Comparative Examples C1-C3) showed little or no blackening of the zinc-iron alloy. Example C4 revealed that DTO did not dissolve at all and was therefore found to be unsuitable for testing. In cases where no blackening was obtained, corrosion resistance was not further tested, as blackening is a fundamental requirement.

[0154] In further comparative examples, the above test passivation compositions (particularly those according to the present invention) were tested on the above substrates, but with a zinc (but not zinc alloy) or zinc-nickel alloy layer thereon. In each further example, no darkening was obtained (i.e., a "-" rating was given). In conclusion, the test passivation compositions used in the method of the present invention darken zinc-iron alloys very specifically.

Claims

1. 1. A method for forming a black passivation layer on a zinc-iron alloy, comprising: (a) providing a substrate comprising the zinc-iron alloy; (b) providing a black passivation composition for depositing the black passivation layer on the zinc-iron alloy, the composition comprising: (i) one or more blackening agents selected from the group consisting of formula (I) and formula (II): 【Chemical 1】 (In the formula, R 1 and R 2 are independently selected from the group consisting of hydrogen and C1-C5 alkyl; R 3 is selected from the group consisting of sulfonic acids, carboxylic acids, alkylcarboxylic acids, phosphonic acids, salts and esters thereof; n is 1, 2, 3, 4, or 5 【Chemistry 2】 (In the formula, R 4 is selected from the group consisting of sulfonic acids, carboxylic acids, alkylcarboxylic acids, phosphonic acids, salts and esters thereof; m is 1, 2, 3, 4, or 5, and (ii) one or more metal ion species selected from the group consisting of trivalent chromium, titanium, and zirconium; and (c) contacting the substrate with the black passivation composition so as to form the black passivation layer on the zinc-iron alloy; The method of claim 1, wherein the amount of iron in the zinc-iron alloy is in the range of 0.1% to 30% by weight, based on the total weight of the zinc-iron alloy.

2. 2. The method according to claim 1, wherein the amount of iron in the zinc-iron alloy is in the range of 0.6% to 28%, preferably 2.1% to 25%, more preferably 3.5% to 22%, even more preferably 4.9% to 18%, and most preferably 6.1% to 15%, by weight, relative to the total weight of the zinc-iron alloy.

3. 3. The method according to claim 1 or 2, wherein the black passivation composition is acidic and preferably has a pH of 1.0 to 4.5, preferably 1.2 to 4.0, more preferably 1.4 to 3.3, even more preferably 1.5 to 2.8, and most preferably 1.6 to 2.

2.

4. 4. The method according to any one of claims 1 to 3, wherein the total concentration of the one or more blackening agents in the black passivation composition ranges from 0.2 mmol / L to 100 mmol / L, preferably from 0.3 mmol / L to 80 mmol / L, more preferably from 0.4 mmol / L to 60 mmol / L, even more preferably from 0.8 mmol / L to 45 mmol / L, and most preferably from 1.6 mmol / L to 38 mmol / L, based on the total volume of the black passivation composition.

5. 5. The method according to any one of claims 1 to 4, wherein the black passivation composition comprises one or more blackening agents of formula (I) in a total concentration ranging from 0.4 mmol / L to 25.0 mmol / L, preferably from 0.6 mmol / L to 20.0 mmol / L, more preferably from 0.8 mmol / L to 12.0 mmol / L, even more preferably from 1.0 mmol / L to 10.0 mmol / L, and most preferably from 1.2 mmol / L to 8.0 mmol / L, based on the total volume of the black passivation composition.

6. R 1 and R 2 are independently selected from the group consisting of hydrogen, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, and tert-butyl, preferably from the group consisting of hydrogen, methyl, ethyl, 1-propyl, and 2-propyl, and most preferably from the group consisting of hydrogen and methyl.

7. R 3 contains at least sulfonic acid, its salts and / or esters, preferably R 3 The method according to any one of claims 1 to 6, wherein n is 3 and n is at least a sulfonic acid, a salt and / or an ester thereof.

8. R 4 contains at least sulfonic acid, its salts and / or esters, preferably R 4 The method according to any one of claims 1 to 7, wherein comprises at least a sulfonic acid, a salt and / or an ester thereof, and m is 3.

9. 9. The method according to any one of claims 1 to 8, wherein the total concentration of the one or more metal ion species is in the range of 0.1 g / L to 30 g / L, preferably 0.2 g / L to 20 g / L, more preferably 0.5 g / L to 14 g / L, even more preferably 0.8 g / L to 10 g / L, and most preferably 1.3 g / L to 6.0 g / L, based on the total volume of the black passivation composition and based on the free ion mass.

10. The method according to any one of claims 1 to 9, wherein the black passivation composition is substantially free of tungsten, preferably free of tungsten.

11. The black passivation composition comprises: (iii) one or more halide ion species; and / or (iv) one or more carboxylic acids and / or salts thereof The method of any one of claims 1 to 10, further comprising:

12. 12. The method according to any one of claims 1 to 11, wherein in step (c), the black passivation composition has a temperature in the range of 10°C to 80°C, preferably 15°C to 65°C, even more preferably 19°C to 45°C, and most preferably 22°C to 38°C.

13. 13. The method according to any one of claims 1 to 12, wherein in step (c), the contacting is carried out for a time period of from 10 seconds to 200 seconds, preferably from 20 seconds to 160 seconds, even more preferably from 40 seconds to 130 seconds, and most preferably from 60 seconds to 100 seconds.

14. 1. A black passivation composition for depositing a black passivation layer on a zinc-iron alloy, comprising: (i) one or more blackening agents selected from the group consisting of formula (I) and formula (II): 【Chemistry 3】 (In the formula, R 1 and R 2 are independently selected from the group consisting of hydrogen and C1-C5 alkyl; R 3 is selected from the group consisting of sulfonic acids, carboxylic acids, alkylcarboxylic acids, phosphonic acids, salts and esters thereof; n is 1, 2, 3, 4, or 5 【Chemistry 4】 (In the formula, R 4 is selected from the group consisting of sulfonic acids, carboxylic acids, alkylcarboxylic acids, phosphonic acids, salts and esters thereof; m is 1, 2, 3, 4, or 5, and (ii) one or more metal ion species selected from the group consisting of trivalent chromium, titanium, and zirconium; Including, provided that it is substantially free, preferably free of nickel ions, cobalt ions, and tungsten ions; The black passivation composition, wherein the amount of iron in the zinc-iron alloy is in the range of 0.1% by weight to 30% by weight, based on the total weight of the zinc-iron alloy.

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