Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
  • C23C22/08—Orthophosphates
  • C23C22/10—Orthophosphates containing oxidants
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/46—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing oxalates
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/78—Pretreatment of the material to be coated
  • C23C22/80—Pretreatment of the material to be coated with solutions containing titanium or zirconium compounds
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/82—After-treatment
  • C23C22/83—Chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2222/00—Aspects relating to chemical surface treatment of metallic material by reaction of the surface with a reactive medium
  • C23C2222/10—Use of solutions containing trivalent chromium but free of hexavalent chromium

Definitions

• the present inventions refers to a method for forming a black-passivation layer on a zinc-iron alloy and a black-passivation composition for depositing a black-passivation layer on such, wherein the black-passivation composition comprises one or more than one blackening agent selected from the group consisting of formula (I) and formula (II) as described hereinafter.
• a protective coating/layer of a metal or metal alloy on the metallic substrate is a widely used and established method.
• a well know principle is the deposition of a zinc or zinc-nickel coating/layer on metallic substrates, such as iron metal substrates.
• Such coating/layers are often called conversion coatings/conversion layers.
• Such conversion coatings/conversion layers typically comprise reaction products (which are insoluble in aqueous media over a wide pH range) of the metallic substrate with a respective conversion treatment solution.
• conversion coatings/conversion layers are additionally passivated with a passivation layer by contacting it with a passivation composition.
• Such passivation compositions and respective methods are known in the art.
• the passivation composition furthermore modifies the color of the conversion coating/conversion layer, for example into a bluish or even dark black color.
• a color modification is often very much desired for optical reasons, in particular in the automotive field.
• EP 1 816 234 B1 refers to an aqueous passivating coating composition for zinc or zinc alloys and method for using same.
• CN 104651823 A refers to a cobalt-free, environmentally friendly trivalent chromium black passivation liquid, comprising tungsten disulfide particles as blackening agent.
• CN'823 is silent with respect to zinc iron alloys.
• WO 97/13888 A1 refers to a non-chromate containing, corrosion-inhibiting coating composition capable of protecting a wide variety of metal surfaces.
• WO 02/49960 A2 refers to specific tripolyphosphates, mixtures thereof, and their use as anti-corrosion agents and as biocides (anti-microbial agents) and, where applicable, as encrustation-inhibiting agents.
• EP 3 360 989 A1 refers to a method for electrolytically passivating an outermost chromium or outermost chromium alloy layer to increase corrosion resistance thereof.
• US 2004/0170848 A1 refers to a corrosion inhibiting composition for coating an article or substrate such as a metal, metal coating, chromated metal coating, and the like comprises a film-forming compound such as a wax or a polymer, and a sulfide salt or thio compound or a derivative of a thio compound. US'848 is silent with respect to blackening.
• the present invention also concerns a respective black-passivation composition as further described below in the text as well as a respective use of said one or more than one blackening agent for blackening a zinc-iron alloy.
• a respective black-passivation composition as further described below in the text as well as a respective use of said one or more than one blackening agent for blackening a zinc-iron alloy.
• features described in regard to the method of the present invention in particular features described as being preferred, apply likewise to the black-passivation composition of the present invention, most preferably to a black-passivation composition described as being preferred, and apply likewise to the use according to the present invention, most preferably to the use described as being preferred.
• ions of trivalent chromium refers to chromium ions with the oxidation number +3 (also called trivalent chromium ions) including the free and complexed form, respectively.
• oxidation number +3 also called trivalent chromium ions
• black-passivation layer also denotes a black-conversion layer.
• the black-passivation layer has a darkness value L* of 40 or below, preferably of 33 or below, most preferably of 25 or below, based on the CIELAB color space definition.
• the method of the present invention is highly specific for a zinc-iron alloy.
• Preferred is a method of the present invention, wherein in the zinc-iron alloy the amount of iron ranges from 0.1 wt.-% to 30 wt.-%, based on the total weight of the zinc-iron alloy, preferably 0.6 wt.-% to 28 wt.-%, more preferably 2.1 wt.-% to 25 wt.-%, even more preferably 3.5 wt.-% to 22 wt.-%, most preferably 4.9 wt.-% to 18 wt.-%, even most preferably 6.1 wt.-% to 15 wt.-%.
• a very preferred amount of iron ranges from 4.9 wt.-% to 30 wt.-%. In this very preferred range, an excellent blackening is easily obtained.
• the method of the present invention generally applies to a zinc-iron alloy.
• Preferred is a method of the present invention, wherein the zinc-iron alloy is present on the substrate as a layer, preferably as a layer resulting from a galvanization process, most preferably from a zinc-iron galvanization process.
• the zinc-iron alloy is distinct from the rest of the substrate. In such a way, the substrate is typically protected from corrosion.
• the substrate comprises iron.
• the substrate preferably comprises a base material, preferably a ferrous base material, more preferably steel, on which the zinc-iron alloy is deposited.
• the zinc-iron alloy is distinct from the rest of the substrate (i.e. is represented by the base material).
• the substrate comprises the zinc-iron alloy in a sense that the substrate itself is made of a zinc-iron alloy.
• the base material is already the zinc-iron alloy and thus, the base material is the substrate.
• the substrate is a metal or metal alloy substrate, preferably the substrate comprises iron, most preferably the substrate comprises iron and is different from the zinc-iron alloy.
• a preferred substrate is selected from the group consisting of screws, bolts, nuts, and automotive parts.
• the substrate is (preferably the substrates are) provided in a barrel or fixed on a rack.
• the method of the present invention is applicable to both kinds.
• a black-passivation composition is utilized, preferably the black-passivation composition of the present invention (see text further below).
• the black-passivation composition is also called a conversion composition.
• the black-passivation composition is aqueous (i.e. comprises water), wherein preferably water has a concentration of more than 50 vol.-% based on the total volume of the black-passivation composition, more preferably of 75 vol.-% or more, most preferably of 90 vol.-% or more.
• water is the only solvent.
• the black-passivation composition is a solution.
• the black-passivation composition is substantially free of, preferably does not comprise, particles (including colloids).
• the black-passivation composition is acidic, preferably having a pH from 1.0 to 4.5, preferably from 1.2 to 4.0, more preferably from 1.4 to 3.3, even more preferably from 1.5 to 2.8, most preferably from 1.6 to 2.2.
• the black-passivation composition comprises one or more than one blackening agent as defined above.
• the one or more than one blackening agent utilized in the black-passivation composition is an organic blackening agent.
• Preferred is a method of the present invention, wherein the black-passivation composition is substantially free of, preferably does not comprise, an inorganic blackening agent.
• An inorganic blackening agent is for example disclosed in CN 104651823 A .
• the black-passivation composition comprises at least one or more than one (preferably one) blackening agent of formula (I).
• a blackening agent of formula (I) provides excellent results (see examples below).
• the black-passivation composition is substantially free of, preferably does not comprise, a blackening agent of formula (II). This most preferably applies if the black-passivation composition comprises already a blackening agent of formula (I).
• the one or more than one blackening agent selected from the group consisting of formula (I) and formula (II) are the only blackening agents in the black-passivation composition.
• the one or more than one blackening agent has 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.
• 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 to 25.0 mmol/L, based on the total volume of the black-passivation composition, 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, most preferably from 1.2 mmol/L to 8.0 mmol/L.
• compounds of formula (I) are the only blackening agents in the black-passivation composition utilized in the method of the present invention. Surprisingly, an 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 very desired to maintain a comparatively low concentration of blackening agents such that the life-time of a respective black-passivation composition is as long as possible. A very preferred total concentration ranges from 0.4 mmol/L to 8.0 mmol/L.
• R 1 and R 2 are independently selected from branched and unbranched C1 to C5 alkyl, preferably unbranched C1 to C5 alkyl.
• R 3 and R 4 are independently selected from the group consisting of ammonium salts and alkaline salts, preferably from the group consisting of ammonium, sodium, and potassium.
• 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 hydrogen, methyl, ethyl, 1-propyl, and 2-propyl, most preferably hydrogen and methyl.
• R 1 and R 2 are alkyl groups, preferably as described above as being preferred.
• n 2, 3, or 4, preferably 3.
• R 3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof.
• Sulfonic acid preferably means ⁇ SO 3 H, wherein " ⁇ ” denotes the covalent bond connecting this group with the rest of the compound of formula (I).
• Carboxylic acid preferably means -COOH, wherein " ⁇ ” denotes the covalent bond connecting this group with the rest of the compound of formula (I).
• Alkyl carboxylic acid preferably means a saturated, branched or unbranched alkyl comprising one or more than one (preferably two) carboxylic acid groups, more preferably 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 it comprises ⁇ C(COOH)(CH 2 ) k COOH, wherein " ⁇ " denotes the covalent bond connecting this group with the rest of the compound of formula (I) and k is an integer ranging from 1 to 5, most preferably it comprises ⁇ C(COOH)CH 2 COOH.
• Phosphonic acid preferably means ⁇ PO 3 H 2 , wherein " ⁇ " denotes the covalent bond connecting this group with the rest of the compound of formula (I).
• ⁇ denotes the covalent bond connecting this group with the rest of the compound of formula (I).
• R 3 applies mutatis mutandis to R 4 in formula (II).
• R 3 comprises at least sulfonic acid, salts and/or esters thereof, preferably R 3 comprises at least sulfonic acid, salts and/or esters thereof, and n is 3.
• R 3 is selected from the group consisting of sulfonic acid, carboxylic acid, phosphonic acid, and salts thereof, most preferably R 3 comprises at least sulfonic acid and/or salts thereof, preferably R 3 comprises at least sulfonic acid and/or salts thereof, and n is 3.
• 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.
• R 4 comprises at least sulfonic acid, salts and/or esters thereof, preferably R 4 comprises at least sulfonic acid, salts and/or esters thereof, and m is 3.
• R 4 is selected from the group consisting of sulfonic acid, carboxylic acid, phosphonic acid, and salts thereof, most preferably R 4 comprises at least sulfonic acid and/or salts thereof, preferably R 4 comprises at least sulfonic acid and/or salts thereof, and m is 3.
• 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 utilized in the method of the present invention comprises one or more than one species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium.
• a very preferred trivalent chromium ion source is an organic and/or inorganic trivalent chromium ion source.
• a preferred organic trivalent chromium ion source is trivalent chromium citrate.
• a preferred inorganic trivalent chromium ion source is trivalent chromium chloride hexahydrate.
• a very preferred total concentration is ranging from 0.1 g/L to 4.0 g/L. If the total concentration is significantly below 0.1 g/L, in many cases a particular desired corrosion resistance is not achieved. In contrast, if the total concentration is significantly above 30 g/L, no further benefit is identified and costs are typically inacceptable.
• the metal ions of trivalent chromium have a total concentration ranging from 0.1 g/L to 8.0 g/L, based on 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 from 1.0 g/L to 3.5 g/L.
• the above mentioned total concentration for metal ions of trivalent chromium applies with the proviso that these ions are the only species of transition metal ions in the black-passivation composition.
• the black-passivation composition is substantially free of, preferably does not comprise, thioglycolic acid and salts thereof.
• a method of the present invention is preferred, wherein the black-passivation 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 formula (I) and formula (II), as defined above.
• the black-passivation composition is substantially free of, preferably does not comprise, nickel ions, preferably is substantially free of, preferably does not comprise, nickel.
• 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 upon utilizing the black-passivation composition. Thus, preferred is a method of the present invention, with the proviso that, if zinc ions are present in the black-passivation composition, they are released from the zinc-iron alloy. In other word, if zinc ions are present, the source is the zinc-iron alloy. After setting up a respective black-passivation composition no zinc ions are typically present. After starting the method of the present invention, the total concentration is very low. Upon utilizing the black-passivation composition the total concentration typically increases.
• zinc ions are present in a total concentration of 10 g/L or below, based on the total volume of the black-passivation composition, preferably of 8 g/L or below, most preferably of 5 g/L or below, after step (C) is carried out multiple times.
• the black-passivation composition is substantially free of, preferably does not comprise, silver ions, preferably is substantially free of, preferably does not comprise, silver.
• the black-passivation composition is substantially free of, preferably does not comprise, intentionally added disulfides.
• the black-passivation composition is substantially free of, preferably does not comprise, intentionally added ionic disulfides and compounds comprising a covalent disulfide.
• the black-passivation composition comprises disulfides, preferably ionic disulfides and/or compounds comprising a covalent disulfide.
• the absence of such compounds is generally preferred.
• 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 upon utilizing the black-passivation composition. After setting up a respective black-passivation composition no iron ions are typically present. After starting the method of the present invention, the total concentration is very low. Upon utilizing the black-passivation composition the total concentration typically increases.
• iron ions are present in a total concentration of 1 g/L or below, based on the total volume of the black-passivation composition, preferably of 0.8 g/L or below, most preferably of 0.5 g/L or below, after step (C) is carried out multiple times.
• the black-passivation composition is substantially free of, preferably does not comprise, tungsten.
• the black-passivation composition is substantially free of, preferably does not comprise, tungsten disulfide particles, preferably is substantially free of, preferably does not comprise, tungsten disulfide.
• the black-passivation composition is substantially free of, preferably does not comprise, silicon dioxide, silicates, a silane, and a silane containing compound, preferably is substantially free of, preferably does not comprise, a silicon-containing compound.
• the black-passivation 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 an excellent corrosion resistance is already achieved even without the presence of a silane and/or a silane containing compound.
• the black-passivation composition is substantially free of, preferably does not comprise, cobalt ions, preferably is substantially free of, preferably does not comprise, cobalt.
• cobalt becomes more and more an environmental issue. Only in very few cases, a method of the present invention is preferred, wherein the black-passivation composition comprises cobalt ions and/or cobalt containing compounds. The presence of cobalt typically increases corrosion resistance of a heat-treated substrate with the black-passivation layer obtained by the method of the present invention.
• Said halogen ions are typically the counter ions of the one or more than one species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium.
• the one or more than one species of halogen ions have a total concentration from 1 g/L to 18 g/L, based on the total volume of the black-passivation composition, preferably from 2 g/L to 15 g/L, even more preferably from 3 g/L to 12 g/L, most preferably from 4 g/L to 10 g/L, even most preferably from 6 g/L to 9 g/L.
• the one or more than one species of halogen ions comprises chloride ions and/or fluoride ions.
• fluoride preferably also serves as complexing agent for the metal ions, most preferably if the one or more than one species of metal ions is selected from the group consisting of titanium and zirconium. Bromide ions are preferably not comprised in the black-passivation composition.
• the chloride ions have a total concentration from 1 g/L to 18 g/L, based on the total volume of the black-passivation composition, preferably from 2 g/L to 15 g/L, even more preferably from 3 g/L to 12 g/L, most preferably from 4 g/L to 10 g/L, even most preferably from 6 g/L to 9 g/L.
• chloride ions are the only species of halogen ions.
• Said one or more than one carboxylic acid and/or salts thereof typically 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 for metal ions of trivalent chromium.
• a preferred dicarboxylic acid and/or salts thereof comprises a C2 to C6 dicarboxylic acid and/or salts thereof, preferably oxalic acid, malonic acid, and/or salts thereof, most preferably oxalic acid and/or salts thereof.
• a preferred tricarboxylic acid and/or salts thereof comprises citric acid and/or salts thereof.
• the one or more than one carboxylic acid and salts thereof have a total concentration from 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 to 70 mmol/L. More preferably, the above total concentration applies with the proviso that the black-passivation composition comprises at least one or more than one dicarboxylic acid and/or salts thereof.
• the oxalic acid and salts thereof have a total concentration from 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 to 70 mmol/L.
• oxalic acid and salts thereof are the only dicarboxylic acids and salts thereof in the black-passivation composition, preferably the only carboxylic acids and salts thereof in the black-passivation composition.
• the black-passivation composition comprises citric acid and/or salts thereof, preferably in a total concentration from 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 to 70 mmol/L.
• citric acid and salts thereof are preferably the only tricarboxylic acid and salts thereof in the black-passivation composition, most preferably the only carboxylic acid and salts thereof in the black-passivation composition.
• Nitrate ions preferably act as oxidizing agent in the black-passivation composition.
• 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 from 0.4 g/L to 15 g/L, even more preferably from 0.8 g/L to 11 g/L, most preferably from 1.2 g/L to 7 g/L, even most preferably from 1.7 g/L to 4.5 g/L.
• step (c) the substrate is contacted with the black-passivation composition, preferably as described above, more preferably as described above as being preferred.
• step (c) the black-passivation composition has a temperature in a range from 10°C to 80°C, preferably from 15°C to 65°C, even more preferably from 19°C to 45°C, most preferably from 22°C to 38°C. If the temperature is significantly exceeding 80°C, in many cases an undesired rapid dissolution (stripping) of the zinc-iron alloy is observed impairing the corrosion resistance. However, if the temperature is too low, in many cases the contacting in step (c) is undesirably long.
• step (c) the contacting is performed for a time period 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. If the time period is significantly exceeding 200 seconds, in many cases an undesired rapid dissolution (stripping) of the zinc-iron alloy is observed impairing the corrosion resistance. However, if the time period is too low, typically the blackening is insufficient and thus, the optical appearance is negatively impaired.
• step (c) is performed without applying an electrical current.
• the substrate is dipped into the black-passivation composition.
• step (c) an indeed very good corrosion resistance is obtained if after step (c) the substrate is further treated in order to increase corrosion resistance.
• step (c) of the method of the present invention is additionally treated with a post-dip composition and/or a sealer composition, preferably as outlined below, either in this order or in reversed order.
• step (c) is followed by step (d) contacting the substrate obtained after step (c) with a post-dip composition such that a post-dipped substrate is obtained.
• the post-dip composition is acidic, preferably has a pH ranging from 3.0 to 6.8, more preferably from 3.5 to 6.5, even more preferably from 4.0 to 6.3, most preferably from 4.3 to 6.0.
• the post-dip composition comprises trivalent chromium ions.
• sealer composition is substantially free of, preferably does not comprise, compounds and ions comprising hexavalent chromium.
• the post-dip composition comprises one or more than one wetting agent.
• the post-dip composition comprises one or more than one complexing agent, preferably for the trivalent chromium ions.
• step (d) the post-dip composition has a temperature in a range from 18°C to 60°C, preferably 20°C to 58°C, more preferably from 28°C to 56°C, even more preferably from 33°C to 54°C, most preferably from 38°C to 50°C.
• step (d) is a method of the present invention, wherein in step (d) the contacting is performed for a time period from 5 seconds to 200 seconds, preferably from 10 seconds to 140 seconds, even more preferably from 20 seconds to 100 seconds, most preferably from 30 seconds to 70 seconds.
• step (d) is followed by step (e) contacting the substrate obtained after step (d) with a sealer composition such that a sealed substrate is obtained.
• the sealer composition is alkaline, preferably has a pH of 9 or higher, more preferably in a range from 9.1 to 12, even more preferably from 9.3 to 11, most preferably from 9.5 to 10.5.
• sealer composition comprises two or more than two organic compounds.
• sealer composition is substantially free of, preferably does not comprise, trivalent chromium ions.
• the sealer composition comprises at least one organic polymer, preferably comprising a polyurethane, a polyalkylene (preferably polyethylene), a polyfluoroalkylene (preferably polytetrafluoroethylene) and/or a polyacrylate.
• sealer composition comprises one or more than one wax.
• the sealer composition comprises one or more than one silicon-containing compound, preferably at least one silane and/or at least one inorganic silicate.
• the at least one inorganic silicate is a colloid.
• step (e) the sealer composition has a temperature in a range from 15°C to 35°C, preferably 17°C to 30°C, more preferably from 19°C to 27°C, most preferably from 21°C to 25°C.
• step (e) is a method of the present invention, wherein in step (e) the contacting is performed for a time period from 5 seconds to 200 seconds, preferably from 10 seconds to 140 seconds, even more preferably from 20 seconds to 100 seconds, most preferably from 30 seconds to 70 seconds.
• step (e) is followed by step (f) drying the substrate obtained after step (e).
• step (f) is carried out at a temperature ranging from 55°C to 95°C, preferably 58°C to 90°C, more preferably from 58°C to 85°C, most preferably from 60°C to 80°C.
• step (f) is carried out for a time period 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.
• a drying step is also carried out after one or more than one of the previous steps, e.g. after step (c), step (d), etc.
• a drying step preferably as defined in step (f) is carried out after step (d) and prior to step (e). This is very preferred because in step (d) the post-dip composition is acidic, wherein in step (e) the sealer composition is alkaline.
• the present invention furthermore refers to a black-passivation composition for depositing a black-passivation layer on a zinc-iron alloy, the composition comprising
• a black-passivation composition of the present invention wherein the black-passivation composition is substantially free of intentionally added zinc ions, preferably does not comprise intentionally added zinc ions.
• zinc ions in view of the method of the present invention in particular applies likewise to the black-passivating composition of the present invention.
• the aforementioned regarding the black-passivation composition utilized in the method of the present invention applies likewise to the black-passivation composition of the present invention. This applies in particular to compounds and ions not contained in the black-passivation composition utilized in the method of the present invention.
• the present invention furthermore refers to the use of one or more than one blackening agent selected from the group consisting of
• the aforementioned regarding the one or more than one blackening agent of formula (I) and (II) (in particular what is defined as being preferred) used in the black-passivation composition which is utilized in the method of the present invention applies likewise to the use of the present invention.
• test passivation compositions were prepared with the numbering as introduced in Table 1 below, each composition is aqueous and generally comprises a species of metal ions; 6 g/L to 8 g/L chloride ions if chromium ions were utilized; 50 mmol/L to 70 mmol/L oxalic acid if chromium ions were utilized or 10 mmol/L to 300 mmol/L fluoride ions if titanium ions and zirconium ions were utilized, respectively, as complexing agents; approximately 1 g/L to 7 g/L nitrate ions; and one of the following compounds abbreviated as below:
• test passivation composition has a pH of approximately 2.
• a plurality of u-shaped iron plate specimens (base material) galvanized with a silver-like 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) was dipped for approximately 90 seconds in the respective test passivation composition, the compositions having a temperature of approximately 22°C.
• a blackening was immediately observed.
• Example C4 revealed that DTO was not soluble at all and, thus, could not be used for testing and is found unsuitable. If no blackening was obtained, corrosion resistance was not further tested because blackening was a basic requirement.
• test passivation compositions in particular according to the present invention were tested with said substrates but having a zinc (no zinc alloy) or a zinc-nickel alloy layer thereon.
• no blackening was obtained (i.e. evaluated as "-").
• the test passivation compositions utilized in the method of the present invention very specifically blacken zinc-iron alloys.

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