US20190145009A1 - Conversion coatings for metal surfaces - Google Patents

Conversion coatings for metal surfaces Download PDF

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US20190145009A1
US20190145009A1 US16/300,069 US201716300069A US2019145009A1 US 20190145009 A1 US20190145009 A1 US 20190145009A1 US 201716300069 A US201716300069 A US 201716300069A US 2019145009 A1 US2019145009 A1 US 2019145009A1
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treatment solution
ions
zinc
conversion coating
acid
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Peter Volk
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Carl Freudenberg KG
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Surtec International GmbH
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    • 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
    • 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
    • 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
    • C23C2222/20—Use of solutions containing silanes

Definitions

  • the invention relates to a treatment solution and a process for producing conversion coatings on metal surfaces, particularly zinc or zinc alloy surfaces, using this treatment solution.
  • the invention further relates to a concentrate for manufacturing the treatment solution and conversion coatings, which can be produced by means of the process in accordance with the invention.
  • the treatment solution in accordance with the invention allows metal materials to obtain a high level of corrosion protection, with the decorative and functional properties of the surfaces simultaneously being achieved or improved. Additionally, it is also possible to avoid known problems when using heavy metal ions, particularly cobalt and chromium(VI) ions.
  • the invention relates to the corrosion protection of metal materials, particularly of zinc-containing surfaces.
  • a widely used and established method in prior art is the application of a metal coating to the metal material to be protected.
  • materials made of iron and steel are for example often galvanized or cadmium-plated, to protect them from corrosive environmental influences.
  • the coating metal may behave in the corrosive medium in an electrochemically more noble or less noble way than the base metal of the material on its own. If the coating metal behaves in a less noble way, it acts in the corrosive medium in line with a cathodic corrosion protection against the base metal as a sacrificial anode.
  • the corrosion protection of the zinc is based on the fact that it is even less precious than the base metal and therefore it initially exclusively attracts the corrosive attack. Although this protective function is desirable, the corrosion products of the coating often lead to undesirable impairments of the decorative and often also the functional properties of the material.
  • so-called conversion coatings especially on cathodically-protecting base coating metals, such as zinc and its alloys.
  • base coating metals such as zinc and its alloys.
  • These are reaction products of the base coating metal with a so-called treatment solution, which are insoluble in aqueous media in a wide pH range.
  • so-called conversion coatings are so-called phosphatings and chromatings.
  • phosphatings the layer to be protected is immersed in an acidic solution containing phosphate ions. The acidic medium results in a partial dissolution of zinc from the coating.
  • the released Zn2+ cations form together with the phosphate ions of the reaction solution form a sparingly soluble zinc phosphate layer on the surface. Since zinc phosphate layers themselves only provide comparatively poor corrosion protection but are an excellent adhesion base for paints and varnishes applied to them, their main application is as a primer for paintings and lacquerings.
  • the surface to be treated is immersed in an acidic solution containing chromium(VI) ions.
  • a chromate coating By applying a chromate coating, the corrosive attack on the coating metal can in turn be greatly delayed and thus the base metal corrosion can be further delayed with respect to applying the coating metal alone.
  • the optical impairment of a component due to environmental influences is also delayed by chromating.
  • the corrosion products of the coating metal in the case of zinc the so-called white rust
  • chromium(VI) compounds have the disadvantage that they have a high carcinogenic potential in addition to their acute toxicity.
  • chromating processes using hexavalent chromium compounds a large number of processes have been established in the meantime that use, among other things, various complexes of trivalent chromium compounds.
  • EP 1346081 A1 describes a process for passivating zinc, cadmium or their alloys, especially zinc-nickel alloys, with a chromium(VI)-free solution containing a weak complexing agent, preferably di- or tricarboxylic acids, preferably chromium(III)oxalate complex and Co2+, in which the Co2+ concentration is more than 30 g/l.
  • a weak complexing agent preferably di- or tricarboxylic acids, preferably chromium(III)oxalate complex and Co2+, in which the Co2+ concentration is more than 30 g/l.
  • cobalt ions are to be classified as harmful to health and their use is restricted by various regulations or is listed as a candidate (such as REACH).
  • fluoride as a complexing agent in conversion baths is basically desirable as it is easy to use in the application and analytically controllable.
  • the invention provides an aqueous treatment solution for producing conversion coatings on metal surfaces, in particular on zinc or zinc alloy surfaces, the treatment solution containing: Cr(III) ions in an amount of 0.1 g/l to 8.0 g/l; zirconium and/or titanium ions in an amount of 0.1 g/l to 15 g/l; organosilane-modified silicon oxide nanoparticles in an amount of 0.1 g/l to 50 g/l; and fluoride ions in an amount of 0.1 g/l to 15 g/l.
  • FIG. 1 Cross-section of a conversion coating produced using the treatment solution 3 in accordance with the invention
  • FIG. 2 Cross-section of a conversion coating produced using the treatment solution 4 in accordance with the invention
  • the object of the invention is to provide a treatment solution of the kind mentioned above, which allows to avoid at least some of the disadvantages mentioned.
  • the treatment solution should be able to produce conversion coatings on metallic surfaces, in particular zinc or zinc alloy surfaces, which offer high corrosion protection and at the same time can be free of cobalt and chromium (VI) compounds.
  • the treatment solution should be able to be free of intentionally added cobalt and chromium(VI) compounds.
  • fluoride it should be possible to use fluoride and still achieve a sufficient layer thickness.
  • the treatment solution makes it possible—despite the use of fluoride ions—to produce conversion coatings with a high coating thickness of more than 100 nm. This is also possible without the use of solutions with high concentrations or high treatment temperatures.
  • Treatment solutions in accordance with the invention can be produced low in or essentially free of volatile organic compounds (VOCs) and are therefore environmentally and/or climate-friendly.
  • VOCs volatile organic compounds
  • the treatment solution in accordance with the invention makes it possible to dispense with the use of metal ions harmful to health, in particular cobalt and chromium(VI) compounds, and still provide conversion coatings on zinc or zinc alloy coatings which offer excellent corrosion protection.
  • Practical tests have shown, for example, that zinc or zinc alloy coatings can be provided with corrosion protection for more than 240 hours by treating them with a treatment solution in accordance with the invention, measured in the salt spray test according to ISO 9227 and/or ASTM B 117-73, even after heat stress, for example at 120° C. for 24 hours until initial attack according to DIN 50961 Chapter 10, of more than 240 hours.
  • the treatment solution in accordance with the invention is essentially free of cobalt and chromium(VI) compounds.
  • the treatment solution preferably contains less than 1 mg/l, preferably less than 0.8 mg/l, in particular less than 0.6 mg/l of chromium(VI) ions.
  • the proportion of chromium(VI) ions can be determined photometrically using diphenyl carbazide.
  • the solution contains less than 10 mg/l, preferably less than 5 mg/l, in particular less than 2 mg/l of cobalt ions. Thereby, the proportion of cobalt ions, measured as cobalt, can be determined using ICP.
  • the Ni ion content in one embodiment of treatment solution is preferably less than 10 mg/l, even more preferably less than 5 mg/l, in particular less than 2 mg/l of nickel ions.
  • the proportion of nickel ions, measured as nickel can be determined by means of ICP.
  • zinc or zinc alloy surfaces is understood in the conventional sense. This includes in particular surfaces of articles such as zinc sheet, zinc die casting, zamac, galvanized steel. Zinc alloys can contain up to 30% of foreign metals such as aluminum, iron and nickel.
  • the passivation solution contains Cr(III) ions in an amount between 0.1 g/l and 8.0 g/l.
  • the proportion of Cr(III) ions, measured as chromium, can be determined by ICP.
  • chromium(III) is that it is less dangerous than chromium(VI).
  • chromium(III) oxide in the conversion layer it can provide a particularly good barrier against corrosive external influences, as it is chemically inert.
  • the passivation solution also contains zirconium and/or titanium ions in an amount between 0.1 g/l and 15 g/l.
  • the proportion of zirconium and/or titanium ions, measured as zirconium and/or titanium, can be determined using ICP.
  • zirconium and/or titanium ions are easily precipitable in combination with chromium. This allows the layer thickness to be further increased, whereby the weight content of zirconium and/or titanium in the conversion layer produced can even be higher than the chromium content.
  • the treatment solution in accordance with the invention contains organosilane-modified silicon oxide nanoparticles.
  • the silicon oxide is preferably present in the form of a nanoscale agglomerate.
  • This agglomerate can be regarded as a core whose surface is silane-modified, i.e. on whose surface organic silane compounds are arranged.
  • Organosilane modification means in particular that oxygen atoms are covalently bonded to silicon atoms of an organic silicon compound at least on the surface of the silicon oxide nanoparticles.
  • the organic silicon compound is preferably an epoxy, amido, ureido, amino, ester, mercapto and/or isocyanate silane.
  • silicon oxide nanoparticles are modified with a different number and/or type of organic silicon compounds. Silicon oxide nanoparticles may also contain various silicon compounds in combination. The stoichiometric composition of the silicon oxide nanoparticles may vary depending on the manufacturing process.
  • the organosilane-modified silica nanoparticles are present in the treatment solution in an amount between 0.1 g/l and 50 g/l in accordance with the invention. These concentration values refer to the total solids' concentration of the organosilane-modified silicon oxide nanoparticles in the treatment solution.
  • the organosilane-modified nanoparticles preferably have an average particle size of 5 to 50 nm.
  • the nanoparticles are advantageously at least partially dispersed in the treatment solution in accordance with the invention.
  • Such nanoparticles can, for example, be produced as described in EP 2406328 A1.
  • suitable nanoparticles are commercially available, for example under the brand name Bindzil® from the company Akzo.
  • organosilane-modified silicon oxide nanoparticles are that they have a high stability even at acid pH values. Another advantage is that the silane modification slows down an attack on the silicon oxide nanoparticles by the fluoride ions used in accordance with the invention.
  • the silicon oxide nanoparticles increase the resistance of the conversion coating.
  • the treatment solution according to invention contains fluoride in a quantity between 0.1 g/l and 15 g/l.
  • fluoride is understood as both free and complex bound fluoride.
  • concentration value refers to the total fluoride content.
  • fluoride in conversion baths is advantageous because it is easy to use and can be controlled analytically, for example by ion-selective potentiometry.
  • fluoride is advantageous for the dissolution of zirconium and/or titanium components because the complexes formed are particularly stable in aqueous environments.
  • the proportion of components contained in the treatment solution may vary depending on the desired performance characteristics. In practical experiments, it has proved to be particularly favorable if the content of:
  • the molar ratio between Cr(III) ions on the one hand and zirconium and/or titanium ions on the other hand in the treatment solution is 0.1 to 2.0, preferably 0.15 to 1.5, particularly preferably 0.2 to 1.
  • chromium (III) salts such as chromium chloride (CrC13), chromium nitrate (Cr(NO3)3), chromium sulfate (Cr2(SO4)3), chromium fluoride (CrF3), chromium methane sulfonate, MSA (Cr2(CH3SO3)3) are preferably used as the source for the chromium (III) ions.
  • the hexafluoro complexes of zirconium and/or titanium as acid and/or their salts can be used as source for the fluoride and simultaneously zirconium and/or titanium ions.
  • complexing agents selected from the group consisting of: Carboxylic acids, in particular formic acid, acetic acid, acetylsalicylic acid, benzoic acid, nitrobenzoic acid, 3,5-dinitrobenzoic acid; amino acids, in particular alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine, chelating ligands, in particular dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids, in particular oxalic, lactic, malonic, succinic, gluta
  • complexing agents selected from the group consisting of: Carboxylic acids, in particular formic acid, acetic acid, acetylsalicylic acid, be
  • chelating agents particularly preferred in accordance with the invention are chelating ligands, for example suitable carboxylic acids, in particular dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids, and/or amino acids as well as suitable mixtures thereof.
  • the complexing agent is selected such that the Cr(III) ions in the treatment solution are at least partially complexed by the complexing agent.
  • the advantage of this is that the process solution is stable in a wide pH range, in particular from pH 1 to pH 5, and the optical appearance of the conversion layer improves and is homogenized.
  • the treatment solution may also contain other metal or metalloid ions.
  • it contains at least one further metal or metalloid ion selected from the group consisting of Na, Ag, Al, Co, Ni, Fe, Ga, In, Lanthanides, Sc, V, Cer, Cr, Mn, Cu, Zn, Y, Nb, Mo, Hf, Ta, W, B, Si, P, Bi, Sb, Se ions, preferably in a concentration between 0.005 and 5 g/l.
  • metal ions can, for example, act as catalysts and are added to the reaction solution preferably as soluble salts, in particular as nitrates, sulphates or halides.
  • the treatment solution may also contain other anions commonly used in generic treatment solutions.
  • they contain at least one anion selected from the group consisting of halide ions, in particular chloride, iodide, sulphur-containing ions, in particular sulphate ions, methane sulphonate, hydrogen sulphate; nitrate ions; phosphorus-containing ions, in particular phosphate ions and anions of esters of phosphoric acid, diphosphate ions, hydrogen phosphate ions, dihydrogen phosphate, linear and/or cyclic oligophosphate ions, linear and/or cyclic polyphosphate ions, phosphonic acids, 1-hydroxyethane-(1,1-diphosphonic acid), aminotrimethylenephosphonic acid, diethylenetriaminepenta(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), 2-phosphonobutane-1,2,4-tricarboxylic acid, hexafluor
  • Nitrate ions, sulphate ions and/or phosphate ions are particularly preferred in accordance with the invention.
  • the pH value of the treatment solution is adjusted to values between about 1.5 and 5, preferably from 2 to 4 and in particular from 2.5 to 3.5.
  • the desired pH value can be adjusted by adding hydrogen ions, i.e. by adding an acid and/or a base.
  • the aqueous treatment solution contains at least one organic and/or inorganic acid.
  • the organic acid is preferably selected from the group consisting of citric acid, malonic acid, formic acid, tartaric acid, lactic acid, malic acid, gluconic acid, ascorbic acid, oxalic acid, succinic acid, and adipic acid.
  • an inorganic acid is used, it is preferably selected from the group consisting of phosphoric acid, polyphosphonic acid, nitric acid, hydrochloric acid and sulfuric acid. In accordance with the invention nitric acid is preferred.
  • the treatment solution contains weak oxidizing agents, preferably selected from nitrite, amine oxides such as hydroxylamine or hydroxylamine compounds, N-oxides such as m-nitrobenzene sulfonate, nitroguanidine 4-picoline N-oxide, N-methylmorpholine N-oxide and derivatives thereof.
  • weak oxidizing agents preferably selected from nitrite, amine oxides such as hydroxylamine or hydroxylamine compounds, N-oxides such as m-nitrobenzene sulfonate, nitroguanidine 4-picoline N-oxide, N-methylmorpholine N-oxide and derivatives thereof.
  • the treatment solution in accordance with the invention advantageously exhibits a content of volatile organic compounds (VOC), for example alcohol, such as methanol or ethanol, of less than 10% by weight, preferably less than 5% by weight, particularly preferably less than 4% by weight, very particularly preferably less than 3% by weight, in particular from 0.001 to 2% by weight, based on the finished composition.
  • VOC volatile organic compounds
  • the VOC content can, for example, be determined by GC or GC/MS.
  • the treatment solution may also contain auxiliary substances, for example selected from the group consisting of polymers, in particular organic polymers, corrosion inhibitors; silicas, in particular colloidal or dispersed silicas; surface-active substances, in particular surfactants; diols, triols, polyols; organic acids, in particular monocarboxylic acids; amines; plastic dispersions; dyes, pigments, in particular carbon black, pigment formers, in particular metallic pigment formers; amino acids, in particular glycine; dispersing auxiliaries.
  • Suitable surfactants are, for example, aliphatic fluorocarbon sulfonates.
  • Another object of the present invention is a concentrate for the production of a treatment solution in accordance with the invention.
  • the concentrate may be in solid or liquid form and preferably has an active substance concentration which allows the treatment solution in accordance with the invention to be produced by dilution with at least 50% by weight, preferably at least 70% by weight, of water relative to the total weight of the treatment solution. Practical trials have shown that it is appropriate to produce the treatment solution from two concentrates of different composition, as this ensures a longer storage stability of the respective concentrates.
  • a further object of the invention is thus a kit comprising at least 2 concentrates of different composition for the preparation of the treatment solution in accordance with the invention.
  • the concentrates preferably have an active substance concentration which, in combination, makes it possible to prepare the treatment solution according to the invention by diluting it with at least 50% by weight and preferably at least 70% by weight of water.
  • workpieces with surfaces made of zinc or zinc alloys can preferably be provided with a conversion coating.
  • workpieces can be passivated if they are provided with a zinc coating produced by alkaline cyanidic, alkaline cyanide-free or acidic non-cyanidic electrolytic zinc deposition, if they are coated with zinc layers from thermal diffusion processes, or if they are galvanized by means of a melt or if they consist of zinc or a zinc alloy at all.
  • Zinc alloys on the workpiece surfaces can be Zn/Fe, Zn/Ni, Zn/Al and Zn/Co alloys.
  • reaction solution can also be used to treat workpieces in accordance with the invention on which, in addition to the zinc or zinc alloy surfaces, surfaces are exposed which do not consist of zinc or a zinc alloy, for example iron-containing surfaces such as steel surfaces. These other surfaces can be passivated together with the zinc or zinc alloy surfaces.
  • reaction solution in accordance with the invention it is also possible to use the reaction solution in accordance with the invention to passivate aluminum, aluminum alloy surfaces, iron and iron alloy surfaces, magnesium and magnesium alloy surfaces and surfaces consisting of and/or containing cadmium.
  • the present invention relates to a process for producing a conversion layer on metallic surfaces, in particular workpieces comprising zinc or zinc alloy layers, in which the workpiece to be treated is brought into contact with a treatment solution in accordance with the invention.
  • the contacting occurs by immersion, i.e. the workpieces are immersed in the treatment solution contained in a container.
  • the workpieces can either be held on racks and immersed in the reaction solution with the racks, or they can be placed in a drum or centrifuge or on a tray and immersed in the reaction solution with the drum or tray.
  • the workpieces are also brought into contact with the treatment solution by spray dipping.
  • the workpieces are also brought into contact with the treatment solution by spraying.
  • the workpieces can also be brought into contact with the treatment solution by flooding.
  • the workpieces can also be sprayed with the treatment solution, for example by means of a nozzle from which a surge of the treatment solution emerges.
  • Another method of treatment is to apply the treatment solution to the workpiece surfaces by brushing, rolling or another application technique. Treatment can take place in conventional facilities in which the workpieces are treated in batches or in continuous flow facilities in which the workpieces are continuously passed through and treated.
  • One advantage of the method in accordance with the invention is that it can be carried out under similar process conditions as commercial methods with treatment solutions containing cobalt. Thus, it is possible to use the installation technology of the prior art.
  • the treatment solution has a bath temperature of about 20 to 100° C., preferably 20 to 80° C., preferably 25 to 60° C., especially preferably 30 to 50° C.
  • the immersion time is preferably between 5 and 700 seconds, more preferably between 15 and 600 seconds, and in particular between 20 and 240 seconds. Depending on the technique with which the workpieces are brought into contact with the reaction solution, longer or shorter treatment times may also be necessary.
  • the workpieces to be treated are first cleaned, if necessary. This process step can also be omitted, for example if the workpieces are brought into contact with the reaction solution immediately after electrolytic galvanizing and subsequent rinsing of the galvanizing solution.
  • the workpieces are preferably dried, for example with warm air.
  • the workpieces can also be rinsed before drying to remove excess reaction solution from the surface.
  • the procedure is single-stage. It is also conceivable, however, that the treated object is treated with another treatment solution, such as a sealing solution, before and/or after the application of the conversion coating.
  • another treatment solution such as a sealing solution
  • Another object of the present invention is a conversion layer produced by a process as described above.
  • the conversion layer contains compounds of the elements Cr, Si, 0, F, C, H, as well as Zr and/or Ti, even more preferably it consists of these compounds, whereby compounds originating from the metallic surface, for example iron and/or zinc, can also be contained.
  • the weight fractions of the elements can be measured by energy disperse X-ray spectroscopy, EDX.
  • Chromium is usually in the range from 0.05 to 2 wt. %, preferably from 0.1 to 1.5 wt. %, even more preferably from 0.15 to 1.3 wt. %, in particular from 0.2 to 1.0 wt. %, in each case based on the total weight of carbon, oxygen, fluorine, silicon, zirconium, titanium, chromium, iron, zinc.
  • the percentage by weight of silicon is usually in the range from 0.05 to 10 wt.
  • % preferably from 0.1 to 7 wt. %, even more preferably from 0.2 to 5 wt. %, in particular from 0.3 to 3 wt. %, in each case based on the total weight of carbon, oxygen, fluorine, silicon, zirconium, titanium, chromium, iron, zinc.
  • the percentage by weight of oxygen is usually in the range from 1 to 25 wt. %, preferably from 1.5 to 22 wt. %, even more preferably from 2 to 20 wt. %, in particular from 3 to 15 wt. %, based in each case on the total weight of carbon, oxygen, fluorine, silicon, zirconium, titanium, chromium, iron, zinc.
  • the percentage by weight of fluorine is usually in the range from 0.05 to 3 wt. %, preferably from 0.1 to 2 wt. %, even more preferably from 0.15 to 1.5 wt. %, in particular from 0.2 to 1.0 wt. %, in each case based on the total weight of carbon, oxygen, fluorine, silicon, zirconium, titanium, chromium, iron, zinc.
  • the percentage by weight of zirconium and/or titanium is usually in the range from 0.1 to 5 wt. %, preferably from 0.2 to 4 wt. %, even more preferably from 0.3 to 3 wt. %, in particular from 0.5 to 2.5 wt. %, in each case based on the total weight of carbon, oxygen, fluorine, silicon, zirconium, titanium, chromium, iron, zinc.
  • the percentage by weight of zirconium and/or titanium in the conversion layer is higher than the percentage of chromium. This, in combination with the silicon oxide nanoparticles, provides particularly good corrosion protection.
  • the conversion layer may also contain other elements such as Ni, Al, Fe, Co, Cd, for example from the treated surface.
  • the thickness of the conversion layer can vary depending on the desired corrosion protection properties. For most applications, it has proven to be convenient to adjust the conversion coating with an average coating thickness from 100 nm to 1000 nm, preferably from 100 nm to 600 nm, and in particular from 150 nm to 400 nm.
  • the coating thickness can be determined by measuring a fracture in the scanning electron microscope.
  • the conversion coating provides corrosion protection in the salt spray test according to ISO 9227 and/or ASTM B 117-73 without or with heat stress, for example at 120° C. for 24 hours, to an object containing zinc or zinc alloy coatings for more than 100 hours, preferably more than 200 hours and in particular more than 240 hours, until initial attack according to DIN 50961 Chapter 10.
  • a further advantage of the conversion coating in accordance with the invention is that it can be produced without coloring components. For example, it can show a clear, transparent and essentially colorless and iridescent appearance on zinc. This facilitates an optional selectively set coloring, for example for easier differentiation of components.
  • the treatment solution in accordance with the invention can be used to reliably and easily differentiate between right-handed and left-handed components by means of targeted coloring. This increases process reliability enormously, especially when processing very similar components in large quantities.
  • the conversion coating may contain dyes or pigments.
  • the conversion layer in accordance with the invention already provides the treated object with excellent corrosion protection. Therefore, it is not necessary to provide it with an additional layer, for example a sealing layer. Nevertheless, the conversion coating in accordance with the invention is excellently suited as a basis for further inorganic and/or organic layers.
  • Objects or articles which have a conversion coating in accordance with the invention can therefore be protected permanently and thus particularly advantageously against corrosion.
  • Objects or articles which have a conversion layer in accordance with the invention are also object of the present invention.
  • Example 2 Treatment of Zinc-Coated Steel Sheets with the Treatment Solutions in Accordance with the Invention
  • the treatment solutions produced in example 1 are used to treat zinc-coated steel sheets.
  • the steel sheets were produced alkaline cyanide-free by use of commercially available SurTec® 704.
  • the treatment parameters are set as follows:
  • Treatment solution 1 2 3 4
  • Treatment temperature 40° C. 40° C. 40° C. 40° C. pH-value 3.2 3.0 3.0 3.0 Tretment duration 2 min 1 min 120 s 120 s
  • Treatment solution 1 2 3 4 Heat stress 120° C. 120° C. 120° C. 120° C. Stress duration 24 h 24 h 24 h 24 h Corrosion protection >240 h >120 h >336 h >336 h until initial attack
  • Example 4 Determination of the Element Composition of the Conversion Coating Produced with Treatment Solution 3
  • composition is measured by energy disperse X-ray spectroscopy (EDX).
  • EDX energy disperse X-ray spectroscopy
  • Example 5 Weight Percentages of the Elements of Different Conversion Coatings in Accordance with the Invention
  • the weight percentage of the elements on a passivated zinc surface in accordance with the invention was measured by means of energy disperse x-ray spectroscopy (EDX) at an excitation voltage of 20 kV and evaluated by means of EDAX Genesis V5.11.
  • EDX energy disperse x-ray spectroscopy
  • FIG. 1 shows the cross-section of the conversion coating produced with treatment solution 3.
  • the thickness of the conversion coating was measured at 10 different points using mean value formation.
  • the average coating thickness is about 300 nm.
  • FIG. 2 shows the cross-section of the conversion coating produced with treatment solution 4.
  • the thickness of the conversion coating was measured at 10 different points using mean value formation.
  • the mean coating thickness is about 250 nm.
  • the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise.
  • the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.

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  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Treatment Of Metals (AREA)
US16/300,069 2016-05-11 2017-05-05 Conversion coatings for metal surfaces Abandoned US20190145009A1 (en)

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DE102016005656.8A DE102016005656A1 (de) 2016-05-11 2016-05-11 Konversionsschichten für metallische Oberflächen
DE102016005656.8 2016-05-11
PCT/EP2017/000560 WO2017194187A1 (fr) 2016-05-11 2017-05-05 Couches de conversion pour surfaces métalliques

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JP7385275B2 (ja) 2020-10-02 2023-11-22 日本表面化学株式会社 コバルトフリーの化成皮膜処理液、及び、それを用いた化成皮膜処理方法
DE102021204609A1 (de) * 2021-05-06 2022-11-10 FNT-GmbH Verfahren zur Beschichtung von Zinkdruckgussteilen, mehrlagige Beschichtung zum Schutz von Zinkdruckgussteilen und beschichtetes Zinkdruckgussteil
DE102022105844A1 (de) 2022-03-14 2023-09-14 Carl Freudenberg Kg Passivierungsschicht für metallhaltige Substrate
DE102022126251A1 (de) 2022-10-11 2024-04-11 Liebherr-Aerospace Lindenberg Gmbh Verfahren zur Oberflächenbehandlung
DE102023001507A1 (de) 2023-04-17 2024-04-04 Mercedes-Benz Group AG Verfahren und Vorrichtung zum Reaktivieren einer Konversionsschicht

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JP2019515143A (ja) 2019-06-06
CN109312467A (zh) 2019-02-05
EP3455392A1 (fr) 2019-03-20
JP6882340B2 (ja) 2021-06-02
WO2017194187A1 (fr) 2017-11-16

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