ES2943158T3 - Method for Forming a Black Passivation Layer on a Zinc-Iron Alloy and Black Passivation Composition - Google Patents

Abstract

The present invention relates to a method of forming a black passivation layer on a zinc-iron alloy of a substrate, a black passivation composition for depositing a black passivation layer thereon, wherein the black passivation composition comprises one or more of a blackening agent selected from the group consisting of formula (I) and formula (II) as described below, and a respective use of said blackening agents for blackening a zinc-iron alloy. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Method for Forming a Black Passivation Layer on a Zinc-Iron Alloy and Black Passivation Composition

field of invention

The present invention relates 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 thereon, wherein the black passivation composition comprises one or more of a blackening agent selected from the group consisting of compounds of formula (I) and formula (II) as described below.

Background of the invention

In order to protect metal substrates from corrosive environmental influences different methods are available according to the prior art. Applying a protective layer/coating of a metal or metal alloy onto a metal substrate is a widely used and established method. A well-known principle is the deposition of a zinc or zinc-nickel coating/layer on metal substrates, such as iron metal substrates. Such coatings/layers are often referred to as conversion coatings/layers. Said conversion coatings/layers typically comprise reaction products (which are insoluble in aqueous media over a wide pH range) of the metal substrate with a respective conversion treatment solution. To further increase corrosion resistance, such conversion coatings/layers are further passivated with a passivation layer by contacting them with a passivation composition. Such passivation compositions and the respective methods are known in the art.

In addition to a zinc and zinc-nickel coating/layer other alloys are becoming more prominent, such as zinc-iron. With nickel becoming increasingly questionable with respect to environmental and health issues, less critical alternatives are desired.

In many cases, the passivation composition further modifies the color of the coating/conversion layer, for example to a bluish or even dark black color. Depending on the application, such a color change is often highly desired for optical reasons, in particular in the automotive field.

However, for certain coatings/conversion layers, adequate color modification caused by means of passivation compositions is not available at all, provides insufficient color modification, deteriorates corrosion resistance after color modification, or requires compositions sophisticated passivation methods, which are difficult to handle. This is especially true for zinc-iron conversion coatings/layers, e.g. g., substrates protected with a zinc-iron layer. Blackening them without compromising corrosion resistance is still in demand.

EP 1816234 B1 relates to an aqueous passivating coating composition for zinc or zinc alloys and a method of using the same.

CN 104651823 A refers to an environmentally friendly, cobalt-free trivalent black chromium passivation liquid comprising tungsten disulfide particles as blackening agent. Document CN'823 is silent with respect to iron and zinc alloys.

WO 97/13888 A1 relates to a chromate-free corrosion-inhibiting coating composition capable of protecting a wide variety of metal surfaces.

WO 02/49960 A2 is concerned with specific tripolyphosphates, mixtures thereof, and their use as anticorrosion agents and as biocides (antimicrobial agents) and, where applicable, as scale inhibitors.

Document EP 3360989 A1 refers to a method for electrolytically passivating an outer layer of chromium or chromium alloy to increase the corrosion resistance thereof.

US 2004/0170848 A1 relates to a corrosion inhibitor composition for coating an article or substrate, such as metal, metal coating, chrome metal coating and the like, comprising a film-forming compound, such as such as a wax or a polymer, and a sulfide salt or a thio-compound or a derivative of a thio-compound. US'848 is silent with regard to blackening.

Although black passivation compositions are described in the art, there is a continuing demand to improve the blackening of zinc-iron conversion coatings/layers.

Objective of the present invention

Therefore, the object of the present invention is to provide a method for forming a black passivation layer particularly on a zinc-iron alloy with improved blackening quality and without compromising corrosion resistance. In addition, a respective black passivation composition is also needed.

Furthermore, the aim is to overcome the aforementioned drawbacks and in particular to provide a method (together with a respective composition), which is easy to handle and prevents sedimentation by being substantially free of particles.

Summary of the invention

The aforementioned objectives are solved by a method for forming a black passivation layer on a zinc-iron alloy, a method that comprises the steps:

(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, which composition comprises

(i) One or more than one blackening agent selected from the group consisting of compounds of formula (I),

R1 and R2 are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, R3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid, salts and esters thereof, and n is 1,2 , 3, 4 or 5,

and formula (II),

where

R4 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid moieties, salts and esters thereof, and

m is 1,2, 3, 4, or 5, and

(ii) One or more species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium, and

(c) Contacting the substrate with said black passivation composition so that the black passivation layer is formed on the zinc-iron alloy.

Using said one or more than one blackening agent, a very good blackening of a zinc-iron alloy together with a good corrosion resistance is obtained. Furthermore, the method of the present invention is simple. and it can be done easily. ^{The present} Inventors' own experiments have also shown that the blackening obtained by means of the method of the present invention and the respective black passivation composition of the present invention is very specific for zinc-iron alloys. Own experiments confirm that zinc alone and zinc-nickel alloys do not blacken. More details are given in the examples section later in the text.

The present invention also relates to a respective black passivation composition as described later in the text, as well as to the respective use of said one or more than one blackening agent for blackening a zinc-iron alloy. In general, the features described with respect to the method of the present invention, in particular the features described as preferred, apply equally to the black passivation composition of the present invention, most preferably to a black passivation composition described as preferred, and apply equally to the use according to the present invention, most preferably to the use described as preferred.

Detailed description of the invention

In the context of the present invention, trivalent chromium ions refers to chromium ions with oxidation number 3 (also called trivalent chromium ions) including the free and complexed forms, respectively. This applies mutatis mutandis to the metal ions of titanium and zirconium, respectively.

In the context of the present invention, the expression "black passivation layer" also indicates a black conversion layer.

the substrate

Preferably, the black passivation layer has a darkness value L* of 40 or less, preferably 33 or less, most preferably 25 or less, based on the CIELAB color space definition.

As mentioned above, the method of the present invention is highly specific for a zinc-iron alloy. A method of the present invention is preferred, wherein in the zinc-iron alloy the amount of iron ranges from 0.1% by weight to 30% by weight, based on the total weight of the zinc-iron alloy, preferably 0.6% by weight to 28% by weight, more preferably 2.1% by weight to 25% by weight, even more preferably 3.5% by weight to 22% by weight, most preferably 4.9% by weight weight to 18% by weight, even most preferably from 6.1% by weight to 15% by weight. A highly preferred amount of iron ranges from 4.9% by weight to 30% by weight. Excellent blackening is easily obtained in this highly preferred range.

The method of the present invention is generally applied to a zinc-iron alloy. A method of the present invention is preferred in which the zinc-iron alloy is present on the substrate as a layer, preferably as a layer resulting from a galvanizing process, most preferably from a zinc-iron galvanizing process. Therefore, most preferred is a method of the present invention in which the zinc-iron alloy is distinct from the remainder of the substrate. In this way, the substrate is normally protected from corrosion.

A method of the present invention is preferred in which the substrate comprises iron. This means that the substrate preferably comprises a base material, preferably a ferrous base material, more preferably steel, on which the zinc-iron alloy is deposited. Therefore, the zinc-iron alloy is distinct from the rest of the substrate (ie, it is represented by the base material).

However, in a few cases, a method of the present invention is preferred in which the substrate comprises the zinc-iron alloy in the sense that the substrate itself is made of a zinc-iron alloy. In other words, preferably the base material is already the zinc-iron alloy and therefore the base material is the substrate.

A method of the present invention is preferred in which the substrate is a metal or metal alloy substrate, preferably the substrate comprises iron, most preferably the substrate comprises iron and is other than zinc-iron alloy.

A method of the present invention is preferred, in which the substrate is a workpiece that requires resistance to anodic corrosion, most preferably required due to corrosion caused by the environment.

Typically, a preferred substrate is selected from the group consisting of screws, bolts, nuts, and auto parts.

A method of the present invention in which more than one substrate is provided in step (a) is preferred, preferably a plurality of substrates is provided in step (a). This applies in particular if the substrate refers to screws, bolts and nuts.

A method of the present invention is preferred in which the substrate (preferably the substrates) is provided in a barrel or fixed in a frame. Thus, the method of the present invention is applicable to both types.

The 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 text below).

Preferably, the black passivation composition is also called a conversion composition.

A method of the present invention is preferred, in which the black passivation composition is aqueous (ie, comprises water), preferably in which the water has a concentration of more than 50% by volume based on the total volume of the black passivation composition, more preferably 75% by volume or more, most preferably 90% by volume or more. Most preferably, water is the only solvent.

Preferably, the black passivation composition is a solution. Therefore, a method of the present invention is preferred in which the black passivation composition is substantially free of particles (including colloids) and preferably does not comprise them.

A method of the present invention is preferred, wherein the black passivation composition is acidic, preferably having 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.

As mentioned above, the black passivation composition comprises one or more than one blackening agent as defined above.

As indicated by formulas (I) and (II), respectively, the one or more of the blackening agents used in the blackened passivation composition is an organic blackening agent. A method of the present invention is preferred in which the black passivation composition is substantially free of, preferably does not comprise, an inorganic blackening agent. An inorganic blackening agent is described, for example, in CN 104651823 A.

A method of the present invention is preferred, wherein the black passivation composition comprises at least one or more than one (preferably one) blackening agent of formula (I). According to own experiments, a blackening agent of formula (I) gives excellent results (see examples below).

In only some cases, a method of the present invention is preferred in which the black passivation composition is substantially free of, preferably does not comprise, a blackening agent of formula (II). This applies most preferably if the black passivation composition already comprises a blackening agent of formula (I).

A method of the present invention is generally preferred, wherein in the black passivation composition one or more than one blackening agent selected from the group consisting of compounds of formula (I) and formula (II) are the sole blackening agents. in the black passivation composition.

A method of the present invention is preferred, wherein in the black passivation composition the one or more blackening agents have a total concentration ranging from 0.2 mmol/L to 100 mmol/L, based on the total volume of the black passivation composition, 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 , most preferably from 1.6 mmol/L to 38 mmol/L.

In particular, a method of the present invention is preferred in which the black passivation composition comprises one or more than one (preferably one) blackening agent of formula (I) in a total concentration ranging from 0.4 mmol/L and 25.0 mmol/L, based on the total volume of the black passivation composition, preferably 0.6 mmol/L to 20.0 mmol/L, more preferably 0.8 mmol/L to 12.0 mmol /L, even more preferably from 1.0 mmol/L to 10.0 mmol/L, most preferably from 1.2 mmol/L to 8.0 mmol/L. Most preferably, in combination with such total concentration, the compounds of formula (I) are the only blackening agents in the black passivation composition used in the method of the present invention. Surprisingly, excellent blackening was obtained even with a comparatively low total concentration of compounds of formula (I), including a total concentration of 0.4 mmol/L. It is highly desirable to maintain a comparatively low concentration of blackening agents so that the lifetime of a respective black passivating composition is as long as possible. A highly preferred total concentration is between 0.4 mmol/L and 8.0 mmol/L.

A method of the present invention is preferred, wherein R1 and R2 are independently selected from branched and unbranched C1 to C5 alkyl, preferably unbranched C1 to C5 alkyl.

A method of the present invention is preferred, wherein in R3 and R4 the salts are independently selected from the group consisting of ammonium salts and alkaline salts, preferably from the group consisting of ammonium, sodium and potassium.

A method of the present invention is preferred, wherein R1 and R2 are independently selected from the group consisting of hydrogen, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, and tert-butyl, preferably hydrogen, methyl, ethyl, 1-propyl and 2-propyl, most preferably hydrogen and methyl.

A method of the present invention is preferred, wherein at least one of R1 and R2 is an alkyl group, preferably as described above as preferred.

A method of the present invention is preferred, wherein n is 2, 3 or 4, preferably 3.

In the method of the present invention, R3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid, salts and esters thereof.

Sulphonic acid preferably means ~S03H, where indicates the covalent bond connecting this group to the remainder of the compound of formula (I). Carboxylic acid preferably means^ -C00H, where "~" indicates the covalent bond connecting this group to the rest of the compound of formula (I). Alkylcarboxylic acid preferably means a saturated, branched or unbranched alkyl comprising one or more than one (preferably two) carboxylic acid groups, more preferably it means a saturated, branched or unbranched C1 to C6 alkyl (preferably C2 to C4 alkyl) comprising one or more than one (preferably two) carboxylic acid groups, even more preferably comprising ~C(C00H)(CH2)kC00H, where "~" indicates the covalent bond connecting this group to the remainder of the compound of formula (I) and k is an integer ranging from 1 to 5, most preferably comprising ~C(C00H)CH2C00H. Phosphonic acid preferably means ~P03H2, where "~" indicates the covalent bond connecting this group to the remainder of the compound of formula (I). Preferably, what is mentioned above with respect to R3 applies mutatis mutandis to R4 in formula (II).

A method of the present invention is preferred, wherein R3 comprises at least sulfonic acid, salts and/or esters thereof, preferably R3 comprises at least sulfonic acid, salts and/or esters thereof, and n is 3.

More preferred is a method of the present invention, wherein R3 is selected from the group consisting of sulfonic acid, carboxylic acid, phosphonic acid, and salts thereof, most preferably R3 comprises at least sulfonic acid and/or salts thereof. , preferably R3 comprises at least sulfonic acid and/or salts thereof, and n is 3.

Most preferred is a method of the present invention, wherein formula (I) comprises the compound 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonic acid, salts and/or esters thereof, preferably 3-(N, N-dimethylthiocarbamoyl)-thiopropanesulfonic acid and/or salts thereof.

A method of the present invention is preferred, wherein m is 2, 3 or 4, preferably 3.

A method of the present invention is preferred wherein R4 comprises at least sulfonic acid, salts and/or esters thereof, preferably R4 comprises at least sulfonic acid, salts and/or esters thereof, and m is 3.

More preferred is a method of the present invention, wherein R4 is selected from the group consisting of sulfonic acid, carboxylic acid, phosphonic acid and salts thereof, more preferably R4 comprises at least sulfonic acid and/or salts thereof, preferably R4 comprises at least sulfonic acid and/or salts thereof, and m is 3.

Most preferred is a method of the present invention, wherein formula (II) comprises the compound 3-(2-benzthiazolylthio)-1-propanesulfonic acid, salts and/or esters thereof, preferably 3-(2-benzthiazolylthio )-1-propanesulfonic acid and/or salts thereof.

The black passivation composition used in the method of the present invention comprises one or more species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium. Although significant blackening of a zinc-iron alloy can already be observed even without the presence of these metal ions, i.e., in the complete absence of these and other transition metal ions, such metal ions are particularly beneficial for obtaining strength. to significant corrosion in addition to the blackening effect. Although some corrosion resistance is present in some cases, the corrosion resistance can be increased significantly further.

A method of the present invention is preferred, wherein the one or more metal ion species is selected from the group consisting of trivalent chromium and titanium. More preferred is a method of the present invention, wherein the one or more than one metal ion species comprises at least trivalent chromium, most preferably the one or more than one metal ion species is trivalent chromium. Own experiments have shown that excellent corrosion resistance results are obtained with trivalent chromium ions.

A method of the present invention is preferred, wherein the trivalent chromium metal ions are derived from an organic and/or inorganic trivalent chromium ion source, preferably from an inorganic trivalent chromium ion source. A highly preferred trivalent chromium ion source is an organic and/or inorganic trivalent chromium ion source. A preferred organic source of trivalent chromium ions is trivalent chromium citrate. A preferred inorganic source of trivalent chromium ions is trivalent chromium chloride hexahydrate.

A method of the present invention is preferred, wherein said one ^or more than one metal ion species has a total concentration ranging from 0.1 g/L to 30 g/L, based on the total volume of the composition of black passivation and in the mass of free ions, preferably from 0.2 g/L to 20 g/L, more preferably from 0.5 g/L to 14 g/L, even more preferably from 0.8 g/L to 10 g/L, most preferably from 1.3 g/L to 6.0 g/L. A highly preferred total concentration ranges from 0.1 g/L to 4.0 g/L. If the total concentration is significantly below 0.1 g/L, in many cases the particular desired corrosion resistance is not achieved. Conversely, if the total concentration is significantly above 30 g/L no additional benefit is identified and the costs are often unacceptable.

Since trivalent chromium ions are preferred, a method of the present invention is preferred, wherein the trivalent chromium metal ions have a total concentration ranging from 0.1 g/L to 8.0 g/L, based on in the total volume of the black passivation composition, preferably from 0.2 g/L to 7.1 g/L, more preferably from 0.5 g/L to 6.1 g/L, even more preferably from 0, 8 g/L to 5.0 g/L, most preferably 1.0 g/L to 3.5 g/L. Most preferably, the aforementioned total concentration for trivalent chromium metal ions is applied with the proviso that these ions are the only transition metal ion species in the black passivation composition.

Listed below are various compounds and ions which are preferably not contained in the black passivation composition used in the method of the present invention. Said compounds/ions are not useful for solving the objectives mentioned in the above scheme or even have a detrimental effect and are therefore avoided. In some cases, the presence of other compounds/ions is unavoidable when using the black passivating composition. Generally, it is preferred to use a comparatively simple black passivation composition.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of hexavalent chromium, preferably does not comprise it. This includes any chromium-containing compounds and ions with an oxidation number of (+VI). It is a very important objective that the method of the present invention avoid any use of hexavalent chromium due to its environmental and health problems.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of, preferably does not comprise, thioglycolic acid and salts thereof. However, in some cases a method of the present invention is preferred, wherein the black passivating composition comprises thioglycolic acid and/or salts thereof in addition to said one or more than one blackening agent selected from the group consisting of compounds of formula (I) and formula (II), as defined above. Although own experiments (data not shown) indicate that the mere presence of thioglycolic acid and/or salts thereof in many cases also cause significant blackening, the results obtained are less good compared to the effect obtained with the blackening agents of formula ( I) and (II).

A method of the present invention is preferred, wherein the black passivation composition is substantially free of, preferably does not comprise, nickel ions, preferably substantially free of, preferably does not comprise, nickel.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of, preferably does not comprise, intentionally added zinc ions. If zinc ions are present in the black passivation composition they are released/dissolved from the zinc-iron alloy when using the black passivation composition. Therefore, a method of the present invention is preferred, provided that, 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, the source is the zinc-iron alloy. After setting up a respective black passivation composition, zinc ions are normally not present. After starting the method of the present invention, the total concentration is very low. By using the black passivation composition, the total concentration is typically increased. Therefore, preferably, the zinc ions are present in a total concentration of 10 g/L or less, based on the total volume of the black passivating composition, preferably 8 g/L or less, most preferably 5 g/L or less, after step (C) is carried out multiple times.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of, preferably does not comprise, silver ions, preferably substantially free of, preferably does not comprise, silver.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of, preferably does not comprise, nicotinic acid and salts thereof.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of, preferably does not comprise, phytic acid and salts thereof.

In most cases, a method of the present invention is preferred, wherein the black passivation composition is substantially free of, preferably does not comprise, intentionally added disulfides. This preferably means that the black passivation composition is substantially free, preferably does not comprise, intentionally added ionic disulfides and covalent disulfide-comprising compounds. In turn, only in very rare cases is a method of the present invention preferred in which the passivating composition black comprises disulfides, preferably ionic disulfides and/or compounds comprising a covalent disulfide. However, in general, the absence of such compounds is usually preferred.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of, preferably does not comprise, intentionally added iron ions. If iron ions are present in the black passivation composition, they are released/dissolved from the zinc-iron alloy when using the black passivation composition. After establishing a respective black passivation composition, no iron ions are normally present. After starting the method of the present invention, the total concentration is very low. By using the black passivation composition, the total concentration is typically increased. Therefore, preferably, the iron ions are present in a total concentration of 1 g/L or less, based on the total volume of the black passivating composition, preferably 0.8 g/L or less, most preferably of 0.5 g/L or less, after step (C) is carried out multiple times.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of tungsten ions, preferably does not comprise them.

More preferred is a method of the present invention, wherein the black passivation composition is substantially free of tungsten, preferably does not comprise it.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of, preferably does not comprise, tungsten disulfide particles, preferably substantially free of, preferably does not comprise, tungsten disulfide.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of thiodiglycol, preferably does not comprise thiodiglycol.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of, preferably does not comprise, silicon dioxide, silicates, a silane and a silane-containing compound, is preferably substantially free of, preferably does not comprise , a compound containing silicon. Only in very rare cases is a method of the present invention preferred in which the black passivating composition comprises a silane and/or a silane-containing compound. It is assumed that in some cases the presence of the silane and/or the silane-containing compound positively affects the corrosion resistance of the black passivation layer. However, in many cases excellent corrosion resistance is already achieved even without the presence of a silane and/or a silane-containing compound.

A method of the present invention is preferred, wherein the black passivation composition is substantially free of, preferably does not comprise, cobalt ions, preferably substantially free of, preferably does not comprise, cobalt. The presence of cobalt is increasingly becoming an environmental problem. Only in very few cases is a method of the present invention preferred in which the black passivation composition comprises cobalt ions and/or cobalt-containing compounds. The presence of cobalt normally increases the corrosion resistance of a substrate heat treated with the black passivation layer obtained by the method of the present invention.

A method of the present invention is preferred, wherein the black passivation composition further comprises

(iii) One or more species of halogen ions, and/or

(iv) One or more than one carboxylic acid and/or its salts.

Said halogen ions are typically the counterions of one or more than one species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium.

A method of the present invention is preferred, wherein one or more halogen ion species have a total concentration of 1 g/L to 18 g/L, based on the total volume of the black passivation composition, 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, even most preferably 6 g/L to 9 g/L L.

A method of the present invention is preferred, wherein one or more halogen ion species comprise chloride ions and/or fluoride ions. In some cases, the fluoride also preferably serves as a complexing agent for metal ions, more preferably if one or more species of metal ions is selected from the group consisting of titanium and zirconium. Bromide ions are preferably not comprised in the black passivating composition.

More preferably, the chloride ions have a total concentration of 1 g/L to 18 g/L, based on the total volume of the black passivating composition, 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, even most preferably 6 g/L to 9 g/L. Most preferably, in the black passivation composition the chloride ions are the only halogen ion species.

Said one ^or more than one carboxylic acid and/or salts thereof normally serve as complexing agents for said one or more than one species of metal ions selected from the group consisting of trivalent chromium, titanium and zirconium, most preferably metal ions of trivalent chromium.

A method of the present invention is preferred, wherein one or more than one c comprises a dicarboxylic acid, a tricarboxylic acid and/or its salts.

A preferred dicarboxylic acid and/or its salts comprises a C2 to C6 dicarboxylic acid and/or its salts, preferably oxalic acid, malonic acid and/or its salts, most preferably oxalic acid and/or its salts.

A preferred tricarboxylic acid and/or salts thereof comprise citric acid and/or salts thereof.

A method of the present invention is preferred, wherein one or more of a carboxylic acid and its salts have a total concentration of 0.5 mmol/L to 120 mmol/L, based on the total volume of the black passivation composition. , preferably from 8 mmol/L to 105 mmol/L, even more preferably from 15 mmol/L to 90 mmol/L, most preferably from 30 mmol/L to 80 mmol/L, even most preferably from 45 mmol/L at 70 mmol/L. More preferably, the above total concentration is applied provided that the black passivating composition comprises at least one or more than one dicarboxylic acid and/or its salts.

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

In some cases, a method of the present invention is preferred, wherein the black passivation composition comprises citric acid and/or salts thereof, preferably in a total concentration of 0.5 mmol/L to 120 mmol/L, based on in the total volume of the black passivation composition, preferably from 8 mmol/L to 105 mmol/L, even more preferably from 15 mmol/L to 90 mmol/L, most preferably from 30 mmol/L to 80 mmol/L, even most preferably from 45 mmol/L to 70 mmol/L. In such cases, citric acid and salts thereof are preferably the only tricarboxylic acid and its salts in the black passivating composition, most preferably the only carboxylic acid and its salts in the black passivating composition.

A method of the present invention is preferred, wherein the black passivation composition further comprises

(v) Nitrate ions.

The nitrate ions preferably act as an oxidizing agent in the black passivating composition.

A method of the present invention is preferred, in which the nitrate ions have a total concentration ranging from 0.1 g/L to 20 g/L, based on the total volume of the black passivation composition, preferably between 0, 4 g/L and 15 g/L, even more preferably 0.8 g/L to 11 g/L, most preferably 1.2 g/L to 7 g/L, even most preferably 1.7 g/L to 4.5 g/L.

Contact with the black passivating composition (step (c))

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

A method of the present invention is preferred, 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 higher. preferably from 19°C to 45°C, most preferably from 22°C to 38°C. If the temperature significantly exceeds 80°C, undesired rapid dissolution (sloughing) of the zinc-iron alloy is observed in many cases which deteriorates corrosion resistance. However, if the temperature is too low, in many cases the contact in step (c) is undesirably long.

A method of the present invention is preferred, wherein in step (c) contact is made for a period of time from 10 seconds to 200 seconds, preferably from 20 seconds to 160 seconds, even more preferably from 40 seconds to 130 seconds. seconds, most preferably from 60 seconds to 100 seconds. If the time period significantly exceeds 200 seconds, undesired rapid dissolution (sloughing) of the zinc-iron alloy is observed in many cases which deteriorates corrosion resistance. However, if the period of time is too short, usually the blackening is insufficient and therefore the optical appearance is negatively deteriorated.

A method of the present invention is preferred, in which step (c) is performed without applying an electric current. Preferably, in step (c) the substrate is dipped into the black passivating composition.

aftercare

As shown in ^the examples below, very good corrosion resistance is actually obtained if after step (c) the substrate is further treated to increase corrosion resistance.

A method of the present invention is generally preferred, in which 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 as described below, either in this order or in reverse order. A method of the present invention is preferred, in which step (c) is followed by step (d) of contacting the substrate obtained after step (c) with a post-immersion composition so as to obtain a post-dip substrate.

A method of the present invention is preferred, wherein the post-dip composition is acidic, preferably has a pH ranging between 3.0 and 6.8, more preferably between 3.5 and 6.5, even more preferably between 4.0 and 6.3, most preferably between 4.3 and 6.0.

A method of the present invention is preferred, wherein the post-dip composition comprises trivalent chromium ions.

A method of the present invention is preferred, wherein the sealant composition is substantially free, preferably does not comprise, hexavalent chromium-comprising compounds and ions.

A method of the present invention is preferred, wherein the post-dip composition comprises phosphate ions.

A method of the present invention is preferred, wherein the post-dip composition comprises one or more than one wetting agent.

A method of the present invention is preferred, wherein the post-dip composition comprises one or more than one complexing agent, preferably trivalent chromium ions.

A method of the present invention is preferred, wherein in step (d) the post-immersion composition has a temperature in the range of 18°C to 60°C, preferably 20°C to 58°C, plus preferably from 28°C to 56°C, even more preferably from 33°C to 54°C, most preferably from 38°C to 50°C.

A method of the present invention is preferred, wherein in step (d) contact is made for a period of time from 5 seconds to 200 seconds, preferably from 10 seconds to 140 seconds, even more preferably from 20 seconds to 100 seconds. seconds, most preferably from 30 seconds to 70 seconds.

A method of the present invention is preferred, in which step (d) is followed by step (e) of contacting the substrate obtained after step (d) with a sealing composition so as to obtain a substrate sealed.

A method of the present invention is preferred, wherein the sealant composition is alkaline, preferably has a pH of 9 or higher, more preferably in the range of 9.1 to 12, even more preferably 9.3 to 11, which more preferably from 9.5 to 10.5.

A method of the present invention is preferred, wherein the sealant composition comprises two or more than two organic compounds.

A method of the present invention is preferred, wherein the sealant composition is substantially free of, preferably does not comprise, trivalent chromium ions.

A method of the present invention is preferred, wherein the sealant composition comprises at least one organic polymer, preferably comprising a polyurethane, a polyalkylene (preferably polyethylene), a polyfluoroalkylene (preferably polytetrafluoroethylene) and/or a polyacrylate.

A method of the present invention is preferred, wherein the sealant composition comprises one or more than one wax.

A method of the present invention is preferred, wherein the sealant composition comprises one or more than one silicon-containing compound, preferably at least one silane and/or at least one inorganic silicate. Preferably, the at least one inorganic silicate is a colloid.

A method of the present invention is preferred, wherein in step (e) the sealant 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, most preferably from 21 °C to 25 °C.

A method of the present invention is preferred, wherein in step (e) contact is made for a period of time from 5 seconds to 200 seconds, preferably from 10 seconds to 140 seconds, even more preferably from 20 seconds to 100 seconds. seconds, most preferably from 30 seconds to 70 seconds.

When steps (d) and (e) are performed as described above in this order, not only a very good black passivation layer is obtained, but also excellent corrosion resistance, most preferably up to 480 hours, depending on the ISO 9227 standard, to the white rust limit of 5%.

A method of the present invention is preferred, in which step (e) is followed by step (f) of drying the substrate obtained after step (e).

A method of the present invention is preferred, wherein step (f) is carried out at a temperature ranging from 55°C to 95°C, preferably 58°C to 90°C, more preferably 58°C. C to 85°C, most preferably 60°C to 80°C.

A method of the present invention is preferred, in which step (f) is carried out for a period of time from 2 minutes to 20 minutes, preferably from 3 minutes to 16 minutes, even more preferably from 4 minutes to 13 minutes. , most preferably from 6 minutes to 10 minutes.

Preferably, a drying step is also carried out, preferably as defined above, after one or more of the above steps, e.g. g., after step (c), step (d), etc. Highly preferred is a method of the present invention, in which a drying step is carried out, preferably as defined in step (f), after step (d) and before step (e). This is highly preferred because in step (d) the post-dip composition is acidic, while in step (e) the sealant composition is alkaline.

The present invention further relates to a black passivation composition for depositing a black passivation layer on a zinc-iron alloy, which composition comprises

(i) One or more than one blackening agent selected from the group consisting of compounds of formula (I)

R1 and R2 are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, R3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid, salts and esters thereof, and

n is 1,2, 3, 4 or 5,

and formula (II),

R4 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid, salts and esters thereof, and

m is 1,2, 3, 4, or 5, and

^{( í í )} One ^or more species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium, in a total concentration ranging from 0.1 g/L to 30 g/L, based on the total volume of the black passivation composition and in the mass of free ions,

with the condition of

- The black passivation composition is substantially free of nickel, cobalt and tungsten ions, and preferably does not comprise them.

In particular, a black passivation composition of the present invention is preferred, wherein the black passivation composition is substantially free of intentionally added zinc ions, preferably does not comprise intentionally added zinc ions. ^Most preferably, what has been mentioned above with respect to zinc ions in view of the method of the present invention in particular applies equally to the black passivation composition of the present invention. Preferably, what has been mentioned above with respect to the black passivation composition used in the method of the present invention (particularly what is defined as preferred) applies equally to the black passivation composition of the present invention. This applies in particular to compounds and ions not contained in the black passivation composition used in the method of the present invention.

The present invention further relates to the use of one ^or more than one blackening agent selected from the group consisting of compounds of formula (I),

R1 and R2 are independently selected from the group consisting of hydrogen and C1 to C5 alkyl,

R3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid, salts and esters thereof, and

n is 1,2, 3, 4 or 5,

and formula (II),

R4 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid, salts and esters thereof, and

m is 1,2, 3, 4 or 5,

to blacken a zinc-iron alloy.

Preferably, the aforementioned with respect to the one ^or more of the blackening agent of formula (I) and (II) (particularly what is defined as preferred) used in the black passivation composition that is used in the method of the present invention equally applies to the use of the present invention.

The present invention is described in more detail by means of the following non-limiting examples.

examples

In ^the examples, several test paslavation compositions were prepared with the numbering presented in Table 1 below, each composition is aqueous and generally comprises a species of metal ions; 6 g/L to 8 g/L of chloride ions if chromium ions were used; 50 mmol/L to 70 mmol/L oxalic acid if chromium ions were used ^or 10 mmol/L to 300 mmol/L fluoride ions if titanium and zirconium ions, respectively, were used as complexing agents; about 1 g/L to 7 g/L of nitrate ions; and one of ^the following abbreviated compounds as follows:

DPS: 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonate sodium salt; also known as Raluplate DPS (CAS 18880-36-9; Raschig Company); a compound of formula (I), wherein R1 and R2 are methyl, R3 is the sodium salt of sulfonic acid, and n is 3;

ZPS: 3-(2-benzthiazolylthio)-1-propanesulfonate sodium salt; also known as Raluplate ZPS (CAS 49625-94-7; Raschig Company); a compound of formula (II), wherein R4 is the sodium salt of sulfonic acid, and m is 3;

SPS: bis-(3-sulfopropyl)-disulfide disodium salt; also known as Raluplate SPS (CAS 27206-35-5; Raschig Company); comparative example;

SPV: 1-(3-Sulfopropyl)-2-vinylpyridinium betaine; also known as Raluplate SPV (CAS 90552-35-5; Raschig Company); comparative example;

MPS: 3-mercaptopropanesulfonate sodium salt; also known as Raluplate MPS (CAS 17636-10-1; Raschig Company); comparative example;

DTO: dithiooxamide; comparative example.

The specific compound and its respective total concentration are described in Table 1 below. Each test passivation composition has a pH of approximately 2.

In each example, as substrates a plurality of U-shaped iron plate specimens (base material) galvanized with a silver-colored zinc-iron layer (Hiron-Zn/Fe for high iron content and Protedur Plus for low iron content). respectively, each is a product of Atotech; for iron content, see Table 1 below) were immersed for approximately 90 seconds in the respective test passivation composition, the compositions having a temperature of approximately 22 2C . In ^the examples according to the invention, blackening was immediately observed.

Subsequently, the treated test pieces were dried and a post-immersion composition (acid, comprising trivalent chromium phosphate) as well as a sealant composition (alkaline, comprising a wax and a silicon-containing compound) were applied. Subsequently, the quality of the blackening was visually evaluated; Corrosion resistance was determined according to ISO 9227.

Table 1

"*" of note; time until the maximum value of 5% white rust was observed,

"#" was also tested on bolts in barrel applications,

"##" tested in compositions with various concentrations,

"n.d." denotes undetermined, typically because there is not (sufficient) blackening,

"+++" denotes excellent blackening; no visual defects are noticeable throughout the test piece,

"++" denotes still acceptable blackening with minor but still acceptable visual defects; the whole test tube is black enough,

"+" denotes no longer acceptable blackening with significant visual defects and areas of the iron-zinc layer,

"-" denotes no or almost no blackening, visual defects, and large areas of the zinc-iron layer.

In all the examples according to the invention (ie examples 1-1, 1-2, 1-3, 1-4 and 11-1) a blackening of a zinc-iron alloy was obtained. Very good results were obtained in examples 1-3 and 1-4, where example 1-4 gave these very good results even in a comparatively wide concentration range for DPS and chromium ions.

In contrast, the alternative compounds (comparative examples C1-C3) provide no or almost no blackening of the zinc-iron alloy. Example C4 revealed that DTO was not soluble at all and therefore could not be used for the assay and was considered unsuitable. If no blackening was obtained, the corrosion resistance was not tested further because blackening was a basic requirement.

In other comparative examples, the above test passivation compositions (particularly according to the present invention) were tested with such substrates but having a zinc (non-zinc alloy) layer or a zinc alloy layer thereon. -nickel. In each additional example no blackening was obtained (ie evaluated as "-"). In conclusion, the test passivation compositions used in the method of the present invention very specifically blacken zinc-iron alloys.

Claims (1)

1. A method for forming a black passivation layer on a zinc-iron alloy, the method comprising the steps: (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, which composition comprises (i) One or more than one blackening agent selected from the group consisting of compounds of formula (I),

R1 and R2 are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, R3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid, salts and esters thereof, and n is 1,2, 3, 4 or 5, and formula (II),

R4 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid, salts and esters thereof, and m is 1,2, 3, 4, or 5, and (ii) One or more species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium, and (c) Contacting the substrate with said black passivation composition so that the black passivation layer is formed on the zinc-iron alloy. The method according to claim 1, wherein in the zinc-iron alloy the amount of iron ranges from 0.1% by weight to 30% by weight, based on the total weight of the zinc-iron alloy, preferably from 0.6% by weight to 28% by weight, more preferably from 2.1% by weight to 25% by weight, even more preferably from 3.5% by weight to 22% by weight, most preferably from 4 0.9% by weight to 18% by weight, even most preferably from 6.1% by weight to 15% by weight. The method according to claim 1 or 2, wherein the black passivation composition is acidic, preferably pH 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. The method according to any of claims 1 to 3, wherein in the black passivation composition one ^or more blackening agents have a total concentration ranging from 0.2 mmol/L to 100 mmol/L, based on the total volume of the blackening passivation composition, 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, most preferably from 1.6 mmol/L to 38 mmol/L. The method according to any of claims 1 to 4, wherein the black passivation composition comprises one or more than one blackening agent of formula (I) in a total concentration ranging from 0.4 mmol/L to 25 0.0 mmol/L, based on the total volume of the black passivation composition, preferably 0.6 mmol/L to 20.0 mmol/L, more preferably 0.8 mmol/L to 12.0 mmol/L , even more preferably from 1.0 mmol/L to 10.0 mmol/L, most preferably from 1.2 mmol/L to 8.0 mmol/L. The method according to any of claims 1 to 5, wherein R1 and R2 are independently selected from the group consisting of hydrogen, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, and tert. -butyl, preferably hydrogen, methyl, ethyl, 1-propyl and 2-propyl, most preferably hydrogen and methyl. 7. The method according to any of claims 1 to 6, wherein R3 comprises at least sulfonic acid, salts and/or esters thereof, preferably R3 comprises at least sulfonic acid, salts and/or esters thereof, and n is 3 . 8. The method according to any of claims 1 to 7, wherein R4 comprises at least sulfonic acid, salts and/or esters thereof, preferably R4 comprises at least sulfonic acid, salts and/or esters thereof, and m is 3 . The method according to any of claims 1 to 8, wherein said one or more than one metal ion species has a total concentration ranging from 0.1 g/L to 30 g/L, based on the total volume of the black passivation composition and in the mass of free ions, preferably from 0.2 g/L to 20 g/L, more preferably from 0.5 g/L to 14 g/L, even more preferably from 0. 8 g/L to 10 g/L, most preferably 1.3 g/L to 6.0 g/L. The method according to any of claims 1 to 9, wherein the black passivation composition is substantially free of tungsten, preferably does not comprise tungsten. The method according to any of claims 1 to 10, wherein the black passivation composition further comprises (iii) One or more species of halogen ions, and/or (iv) One or more than one carboxylic acid and/or its salts. The method according to any of claims 1 to 11, wherein in step (c) the black passivation composition has a temperature in a range of 10°C to 80°C, preferably 15°C to 65°C. C, even more preferably from 19°C to 45°C, most preferably from 22°C to 38°C. The method according to any of claims 1 to 12, wherein in step (c) the contact is made for a period of time from 10 seconds to 200 seconds, preferably from 20 seconds to 160 seconds, even more preferably from 40 seconds. to 130 seconds, most preferably from 60 seconds to 100 seconds. 14. A black passivation composition for depositing a black passivation layer on a zinc-iron alloy, which composition comprises (i) One or more than one blackening agent selected from the group consisting of compounds of formula (I),

( YO ) , where R1 and R2 are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, R3 is selected from the group consisting of sulfonic acid, carbonic acid, carbonic acid, phosphonic acid, salts and esters thereof, and n is 1,2, 3, 4 or 5, and formula (II),

R4 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid, salts and esters thereof, and m is 1,2, 3, 4, or 5, and (ii) One or more species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium, in a total concentration ranging from 0.1 g/L to 30 g/L, based on the total volume of the composition of black passivation and in the mass of free ions, with the condition of - The black passivation composition is substantially free of nickel, cobalt and tungsten ions, and preferably does not comprise them. 15. Use of one or more than one blackening agent selected from the group consisting of compounds of formula (I),

R1 and R2 are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, R3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid, salts and esters thereof, and n is 1, 2, 3, 4 or 5, and from formula (II),

where R4 is selected from the group consisting of sulfonic acid, carboxylic acid, alkylcarboxylic acid, phosphonic acid, salts and esters thereof, and m is 1,2, 3, 4 or 5, to blacken a zinc-iron alloy.