A method for depositing a chromium-containing passivation layer on a passivation composition and a zinc or zinc-nickel coated substrate.

Abstract

The present invention provides a passivation composition for depositing a chromium-containing passivation layer on a substrate coated with zinc or zinc-nickel. [Solution] A passivation composition comprising: (i) trivalent chromium ions; (ii) at least one complexing agent for trivalent chromium ions, which is different from at least one corrosion inhibitor; and (iii) at least one corrosion inhibitor, which comprises (A) one or more substituted azole compounds and / or salts thereof in a total concentration of less than 10 mg / L based on the total volume of the passivation composition, and / or (B) one or more unsubstituted or substituted aliphatic organic acids and / or salts thereof having at least one mercapto group in a total concentration in the range of 0.001 mg / L to 100 mg / L based on the total volume of the passivation composition.

Description

Technical Field

[0001] The first aspect of the present invention relates to a passivation composition for depositing a chromium-containing passivation layer on a substrate coated with zinc or zinc-nickel. According to a second aspect, the present invention relates to a method for depositing a chromium-containing passivation layer on a substrate coated with zinc or zinc-nickel. According to a third aspect, the present invention relates to a substrate coated with zinc or zinc-nickel having a chromium-containing passivation layer on top, obtained by the deposition method according to the second aspect.

[0002] Background of the Invention To protect metal substrates from the influence of corrosive environments, various methods are available according to the prior art. Applying a protective film of a metal or metal alloy on a metal substrate is a widely used and established method. A well-known principle is the deposition of a zinc or zinc-nickel film on a metal substrate such as an iron-based metal substrate, also known as a conversion coating treatment. Such conversion coatings typically contain reaction products (insoluble in an aqueous medium over a wide pH range) of the metal substrate and the respective conversion treatment solutions. To further enhance corrosion resistance, such conversion treatment layers are further passivated with a passivation layer by contacting the respective substrates with a passivation composition. Such passivation compositions and the respective methods are known in the art.

[0003] In many cases, the passivation composition contains trivalent chromium ions in an acidic solution (see, for example, German Patent Application Publication No. 19638176). For example, when a substrate coated with zinc or zinc-nickel contacts such a composition, typically a part of zinc and / or nickel dissolves. Without applying an electric current, a chromium(III) hydroxide passivation layer or a μ-oxo or μ-hydroxy bridged chromium(III) passivation layer is deposited on the surface of the coated substrate. As a result, a dense passivation layer is obtained on the substrate coated with zinc or zinc-nickel.

[0004] A composition for depositing a chromium-containing passivation layer is described in the prior art.

[0005] European Patent Application Publication No. 0479289 describes a chromate treatment process in which a substrate is immersed in a treatment solution containing chromium(VI) and chromium(III) ions, as well as hydrofluoric acid, phosphoric acid, and a silane coupling agent.

[0006] European Patent No. 0922785 describes a treatment solution and method for generating a protective layer on a metal, wherein the surface to be protected comes into contact with a treatment solution containing chromium(III) ions, an oxidizing agent, and an oxygen acid or oxysodium salt of phosphorus or a suitable anhydride. This treatment solution may further contain a monomeric silane coupling agent.

[0007] European Patent No. 1051539 describes a treatment solution for enhancing the corrosion resistance of a substrate, comprising chromium(VI) and chromium(III) ions, phosphoric acid, hydrofluoric acid, colloidal silicon dioxide, and monomeric epoxy-functionalized silane.

[0008] International Publication No. 2008 / 14166 describes a treatment solution for producing protective coatings. This treatment solution comprises zinc ions, phosphoric acid or acidic phosphate, an organic or inorganic anion containing one of the elements boron, silicon, titanium, or zirconium, trivalent chromium ions, and an inorganic or organic peroxide compound as an oxidizing agent.

[0009] Japanese Patent Publication No. 2007-239002 discloses that iron dissolution of the substrate can be suppressed by applying zinc plating and subsequent chromate treatment.

[0010] U.S. Patent Application Publication No. 2006 / 237098 relates to a composition and a method of using the composition to provide a protective coating on various metal substrates.

[0011] Chinese Patent Application Publication No. 108914106 relates to a metal surface treatment liquid, and more particularly to a zinc-plated sheet surface passivation self-filling treatment liquid that is non-toxic and can achieve long-term self-filling protection.

[0012] European Patent Application Publication No. 3045564 relates to a treatment solution for a black trivalent chromium conversion coating. The treatment solution comprises a trivalent chromium compound, two or more organic acids or organic acid salts or one or more organic sulfur compounds, and nitrate ions, but does not contain cobalt compounds.

[0013] European Patent Application Publication No. 2189551 relates to a trivalent chromium conversion coating in which hexavalent chromium is substantially released.

[0014] The passivation compositions described in the prior art often fail to provide a chromium-containing passivation layer with excellent corrosion resistance and / or functional properties, decorative properties, and / or the desired color of the corresponding chromium-containing passivation layer.

[0015] Furthermore, despite such passivation, an increase in the concentration of iron ions in the passivation composition is often observed. This typically occurs due to partial dissolution of the substrate, particularly when the zinc or zinc-nickel protective coating is damaged. Relatively high iron ion concentrations often result in undesirable discoloration of the substrate and can even impair its corrosion resistance. In addition, each passivation composition must be replaced more frequently, requiring costly wastewater treatment before disposal. Therefore, there is an ongoing need to improve existing passivation compositions, especially to extend their lifespan without compromising their corrosion-preventive properties.

[0016] Purpose of the invention Therefore, the object of the present invention was to provide passivation compositions and methods for depositing a chromium-containing passivation layer on a nickel or zinc-nickel coated substrate, as well as the corresponding passivated substrate. This provides, on the one hand, excellent corrosion resistance and on the other hand, an improved lifespan of the passivation composition, and thus a more sustainable passivation method even in the presence of contaminating metal ions such as iron ions. Furthermore, the resulting chromium-containing passivation layer should provide a uniform color, ideally blue or at least bluish.

[0017] Summary of the Invention The above objective is achieved, according to a first aspect, by a passivation composition for depositing a chromium-containing passivation layer on a zinc or zinc-nickel coated substrate, the composition being (i) Trivalent chromium ions, (ii) at least one complexing agent for trivalent chromium ions, which is different from at least one corrosion inhibitor, and (iii) at least one corrosion inhibitor, (A) One or more unsubstituted or substituted (preferably substituted, most preferably substituted only, with no unsubstituted) azole compounds and / or salts thereof, with a total concentration of less than 10 mg / L based on the total volume of the passivation composition. Furthermore / or (preferably or) (B) Based on the total volume of the passivation composition, one or more unsubstituted or substituted aliphatic organic acids and / or salts thereof having at least one mercapto group, with a total concentration ranging from 0.001 mg / L to 100 mg / L. At least one type of corrosion inhibitor, It contains.

[0018] Excellent corrosion resistance to a zinc or zinc-nickel coated substrate can be obtained by using one or more unsubstituted or substituted (preferably substituted, most preferably substituted only, without unsubstituted) azole compounds (including their salts) within a specified concentration range as a corrosion inhibitor (A), and / or (preferably or) using one or more unsubstituted or substituted aliphatic organic acids (including their salts) having at least one mercapto group within a specified concentration range as a corrosion inhibitor (B). Typically, a blue or bluish chromium-containing passivation layer is obtained.

[0019] Furthermore, by using corrosion inhibitors (A) and / or (B) (preferably or), the release of iron ions from the substrate to the passivation composition is significantly suppressed. As a result, each passivation composition is used for a much longer period, preferably in each passivation method, preferably in the method of the present invention, compared to a passivation composition that is identical except for not containing corrosion inhibitors (A) and / or (B).

[0020] The above objective is further solved according to a second embodiment of a method by which a chromium-containing passivation layer is deposited on a substrate coated with zinc or zinc-nickel, and this method is (a) A step of preparing a substrate coated with zinc or zinc-nickel, (b) A step of preparing a passivation composition for depositing a chromium-containing passivation layer on a zinc or zinc-nickel coated substrate, wherein the composition is (i) Trivalent chromium ions, (ii) at least one complexing agent for trivalent chromium ions, which is different from at least one corrosion inhibitor, and (iii) at least one corrosion inhibitor, (A) One or more unsubstituted or substituted (preferably substituted) azole compounds and / or salts thereof, with a total concentration of less than 10 mg / L based on the total volume of the passivation composition. Furthermore / or (preferably or) (B) At least one unsubstituted or substituted aliphatic organic acid having at least one mercapto group and / or its salt, with a total concentration in the range of 0.1 mg / L to 100 mg / L in total, based on the total volume of the passivation composition, and at least one corrosion inhibitor which is contained in the step, and (c) A step of contacting a zinc or zinc-nickel coated substrate with the passivation composition such that a chromium-containing passivation layer is deposited on the zinc or zinc-nickel coated substrate, are included.

[0021] The above-mentioned matters regarding the passivation composition of the present invention also apply to the method of the present invention in the same manner.

[0022] As described above, at least one complexing agent for trivalent chromium ions is different from at least one corrosion inhibitor. In other words, at least one corrosion inhibitor is different from at least one complexing agent for trivalent chromium ions. Therefore, (ii) and (iii) are not the same compound, but different compounds and are different from each other.

[0023] Brief Explanation of the Tables Table 1 shows a schematic correlation between 3-mercaptotriazole (3-MTA) at various concentrations and the optical appearance and corrosion resistance (NSS test).

[0024] Table 2 shows a schematic correlation between 3-mercaptotriazole (3-MTA) at various concentrations and the suppression of iron ion release.

[0025] Table 3 shows a schematic correlation between 3-mercaptopropionic acid (3-MPA) at various concentrations and the suppression of iron ion release.

[0026] Details are shown in the "Examples" section of the following specification.

[0027] Detailed Description of the Invention In relation to the present invention, the terms “at least one” or “one or more” mean “one, two, three, or more than three” (and are further interchangeable with these). Furthermore, “trivalent chromium” refers to chromium with an oxidation state of +3. The term “trivalent chromium ion” refers to Cr in free or complexed form. 3+ It refers to ions.

[0028] In relation to the present invention, the term "chromium-containing passivation layer" refers to a layer (sometimes also referred to as a film) that preferably contains a trivalent chromium compound. Such a chromium-containing passivation layer preferably contains trivalent chromium hydroxide. In some cases, the passivation layer preferably contains an additional metal, preferably cobalt.

[0029] In relation to the present invention, the zinc or zinc-nickel coated substrate contains iron. This means that the substrate contains a base material on which a zinc or zinc-nickel film is deposited, preferably an iron-based material, more preferably steel. Therefore, preferably, iron ions are released from the substrate and the base material, respectively, which occurs particularly when the zinc or zinc-nickel film is damaged.

[0030] The passivation composition of the present invention is preferably an aqueous composition, and preferably the concentration of water is more than 50% by volume, more preferably more than 75% by volume, and most preferably more than 90% by volume, based on the total volume of the aqueous composition.

[0031] The passivation composition of the present invention is preferred for depositing a blue (or bluish) chromium-containing passivation layer on a substrate coated with zinc or zinc-nickel.

[0032] The passivation composition of the present invention is preferred in which one or more substituted azole compounds and / or salts thereof contain one or more substituents selected from the group consisting of amino, nitro, carboxy, hydroxy, sulfonate, and thiol, preferably the substituent being a thiol group.

[0033] The passivation composition of the present invention is preferred in which one or more unsubstituted or substituted (preferably substituted) azole compounds and / or salts thereof are selected from the group consisting of monoazoles, diazoles, triazoles, and tetrazoles, preferably diazoles and triazoles, and most preferably triazoles.

[0034] The passivation composition of the present invention is preferably one in which one or more unsubstituted or substituted (preferably substituted) azole compounds and / or salts thereof are selected from the group consisting of 1,2,4-triazole. Most preferably, this means 1,2,4-H-triazole.

[0035] The passivation composition of the present invention is preferred, wherein one or more substituted azole compounds and / or salts thereof contain at least mercaptotriazole, preferably at least 3-mercapto-1,2,4-triazole (most preferably representing 3-mercapto-1,2,4-H-triazole).

[0036] The term "total concentration less than 10 mg / L" means that (A) is present, but at most less than 10 mg / L. 10 mg / L is explicitly excluded. This expression also means that 0 mg / L is excluded. The passivation composition of the present invention is preferred in which at least one corrosion inhibitor (A) has a total concentration in the range of 0.0001 mg / L to 9.9999 mg / L, preferably 0.01 mg / L to 9.9 mg / L, more preferably 0.1 mg / L to 9.8 mg / L, even more preferably 0.5 mg / L to 9.7 mg / L, even more preferably 1.0 mg / L to 9.6 mg / L, most preferably 2.0 mg / L to 9.5 mg / L, and most preferably 3.0 mg / L to 9.4 mg / L, based on the total volume of the passivation composition.

[0037] Our own experiments have shown that corrosion inhibitor (A), preferably the corrosion inhibitor (A) specified above as preferred, more preferably within the concentration range specified above, effectively suppresses the release of iron ions from the substrate and provides excellent corrosion protection. When the concentration of corrosion inhibitor (A) significantly exceeds 9.9999 mg / L, insufficient corrosion protection is often observed (see the examples below).

[0038] With respect to the corrosion inhibitor (B), the passivation composition of the present invention is preferred in which one or more unsubstituted or substituted aliphatic organic acids and / or salts thereof having at least one mercapto group are carboxylic acids.

[0039] A more preferable passivation composition of the present invention is one or more unsubstituted or substituted aliphatic organic acids and / or salts thereof having at least one mercapto group, which include a monocarboxylic acid.

[0040] The passivation composition of the present invention is preferred, wherein one or more unsubstituted or substituted aliphatic organic acids and / or salts thereof having at least one mercapto group contain 1 to 12 carbon atoms, preferably 2 to 10 carbon atoms, more preferably 3 to 8 carbon atoms, and most preferably 3 to 6 carbon atoms.

[0041] The passivation composition of the present invention is preferred in which one or more unsubstituted or substituted aliphatic organic acids and / or salts thereof having at least one mercapto group comprises 3-mercaptopropionic acid and / or salts thereof, most preferably 3-mercaptopropionic acid.

[0042] The passivation composition of the present invention is preferable in which at least one corrosion inhibitor (B) has a total concentration in the range of 0.01 mg / L to 90 mg / L, preferably 0.1 mg / L to 80 mg / L, more preferably 1 mg / L to 50 mg / L, even more preferably 2 mg / L to 35 mg / L, and most preferably 3 mg / L to 20 mg / L, based on the total volume of the passivation composition.

[0043] Similarly, in our own experiments, corrosion inhibitor (B), preferably the corrosion inhibitor (B) specified above as preferred, more preferably within the concentration range specified above, effectively suppresses the release of iron ions from the substrate and provides excellent corrosion protection. When the concentration of corrosion inhibitor (B) significantly exceeds 100 mg / L, insufficient corrosion protection is usually observed (see the examples below).

[0044] Although corrosion inhibitors (A) and (B) may be used together, it is generally preferable that either corrosion inhibitor (A) or corrosion inhibitor (B) is used in the passivation composition of the present invention. Typically, excellent results can be obtained by using only one of (A) and (B) in the passivation composition of the present invention.

[0045] The passivation composition of the present invention is preferable in which the passivation composition contains trivalent chromium ions at a total concentration of 0.1 g / L to 25 g / L, preferably 0.2 g / L to 20 g / L, more preferably 0.35 g / L to 15 g / L, even more preferably 0.5 g / L to 10 g / L, and most preferably 1.0 g / L to 8 g / L, based on the total volume of the passivation composition.

[0046] In some cases, the passivation composition of the present invention is very preferable if it contains trivalent chromium ions in a total concentration of 0.5 g / L to 2.5 g / L.

[0047] When the total concentration falls significantly below 0.1 g / L, insufficient passivation typically occurs.

[0048] The passivation composition of the present invention is preferred in which at least one complexing agent for trivalent chromium ions is selected from the group consisting of organic complexing agents and inorganic complexing agents. However, the organic complexing agent is different from the at least one corrosion inhibitor as defined throughout this specification.

[0049] The passivation composition of the present invention is preferred in which at least one complexing agent for trivalent chromium ions is selected from the group consisting of monocarboxylic acids, dicarboxylic acids, salts thereof (both monocarboxylic acids and dicarboxylic acids), halogen ions, and mixtures thereof, and preferably contains at least one dicarboxylic acid.

[0050] The passivation composition of the present invention is preferred in which at least one complexing agent for the trivalent chromium ion is selected from the group consisting of unsubstituted monocarboxylic acids, hydroxyl-substituted monocarboxylic acids, amino-substituted monocarboxylic acids, unsubstituted dicarboxylic acids, hydroxyl-substituted dicarboxylic acids, amino-substituted dicarboxylic acids, salts thereof (of all the acids mentioned above), halogen ions, and mixtures thereof, preferably at least one dicarboxylic acid.

[0051] The passivation composition of the present invention is preferred in which at least one complexing agent for trivalent chromium ions is selected from the group consisting of oxalate / oxalic acid, acetate / acetic acid, tartrate / tartaric acid, malate / malic acid, succinate / succinic acid, gluconate / gluconic acid, glutamate / glutamic acid, glycolate / glycolic acid, diglycolate / diglycolic acid, ascorbate / ascorbic acid, and butyrate / butyric acid.

[0052] A passivation composition of the present invention containing a halogen ion and a fluoride is preferred.

[0053] A passivation composition of the present invention is preferred in which at least one complexing agent for trivalent chromium ions does not contain a mercapto group.

[0054] In some cases, the passivation composition of the present invention is preferred, wherein at least one complexing agent for trivalent chromium ions has a total concentration in the range of 0.3 mol / L to 2.0 mol / L, preferably 0.4 mol / L to 1.9 mol / L, more preferably 0.5 mol / L to 1.8 mol / L, and even more preferably 0.6 mol / L to 1.7 mol / L, based on 1 mol / L of trivalent chromium ions in the passivation composition.

[0055] A passivation composition of the present invention is also preferred in which at least one complexing agent for trivalent chromium ions has a total concentration in the range of 1.0% to 15.0% by weight, preferably 2.0% to 14.0% by weight, more preferably 3.0% to 13.0% by weight, even more preferably 4.0% to 12.0% by weight, and most preferably 5.0% to 11.0% by weight, based on the total weight of the passivation composition.

[0056] Typically, within the preferred concentration range defined above, trivalent chromium ions are efficiently stabilized in the passivation composition by a complexing agent (preferably one of the preferred complexing agents).

[0057] In some cases, (iv) preferably a total concentration of divalent cobalt ions of 1.0% to 5.0% by weight, preferably 2.5% to 3.0% by weight, based on the total weight of the passivation composition. A passivation composition of the present invention further containing is preferable.

[0058] In many cases, cobalt ions have a beneficial effect on optional heat treatments (see later sections of this specification for details on heat treatments).

[0059] In the specific alternative passivation compositions described herein, the passivation composition is (i) Trivalent chromium ions, (ii) at least one complexing agent for trivalent chromium ions, which is different from at least one corrosion inhibitor, and (iii) at least one corrosion inhibitor, (A) Based on the total volume of the passivation composition, one or more unsubstituted or substituted (preferably substituted) azole compounds and / or salts thereof, with a total concentration of 0.001 mg / L to 100 mg / L. and / or (B) Based on the total volume of the passivation composition, one or more unsubstituted or substituted aliphatic organic acids and / or salts thereof having at least one mercapto group, with a total concentration ranging from 0.001 mg / L to 100 mg / L. At least one type of corrosion inhibitor, (iv) preferably a total concentration of divalent cobalt ions of 1.0% to 5.0% by weight, preferably 2.5% to 3.0% by weight, based on the total weight of the passivation composition. Includes.

[0060] In this particular passivation composition according to this specification, a preferred total concentration of (B) is preferably applied to (A). Preferably, the characteristics of the passivation composition of the present invention are also applicable to alternative passivation compositions.

[0061] However, in some cases, the passivation composition of the present invention is preferable in which the passivation composition is essentially free of or does not contain divalent cobalt ions, preferably essentially free of or does not contain cobalt ions, and most preferably essentially free of or does not contain cobalt. By eliminating cobalt or cobalt ions from the passivation composition instead, the use of expensive cobalt compounds is avoided, typically resulting in cost savings, and wastewater treatment is simplified without compromising corrosion protection quality.

[0062] The passivation composition of the present invention is preferably having a pH in the range of 0.5 to 5.0, preferably 1.0 to 4.0, more preferably 1.4 to 3.0, even more preferably 1.6 to 2.5, and most preferably 1.8 to 2.3. If the pH is significantly above 5.0, undesirable precipitation may be observed in some cases. If the pH is significantly below 0.5, undesirable strong dissolution of the coated substrate may be observed in some cases. The preferred pH range defined above is particularly beneficial for effectively depositing the chromium-containing passivation layer and maintaining a relatively long lifespan of the passivation composition.

[0063] (v) Based on the total volume of the passivation composition, a total concentration of iron ions of 0 mg / L to 500 mg / L, preferably 0 mg / L to 400 mg / L, more preferably 0 mg / L to 300 mg / L, most preferably 0 mg / L to 250 mg / L, and even more preferably 0 mg / L to 200 mg / L. A passivation composition of the present invention further containing is preferable.

[0064] Due to the presence of corrosion inhibitors (A) and / or (B), relatively high concentrations of iron ions are tolerated without compromising the quality of corrosion protection, thereby extending the lifespan of each passivation composition.

[0065] In some cases, iron ions may be present permanently at very low concentrations, most preferably not even reaching the upper concentration limits specified above. This is not significant in light of the present invention. Typical very low concentrations of iron ions are preferably 0.001 mg / L or higher, more preferably 0.01 mg / L, even more preferably 0.1 mg / L, and most preferably 1 mg / L, based on the total volume of the passivation composition. Preferably, such low concentrations are combined with the upper concentration limits specified above.

[0066] A second aspect of the present invention provides a method for depositing a chromium-containing passivation layer (preferably a blue or bluish chromium-containing passivation layer) on a zinc or zinc-nickel coated substrate, the method comprising: (a) A step of preparing a substrate coated with zinc or zinc-nickel, (b) A step of preparing a passivation composition for depositing a chromium-containing passivation layer on a zinc or zinc-nickel coated substrate (preferably as defined above, more preferably as defined above), wherein the composition is (i) Trivalent chromium ions, (ii) at least one complexing agent for trivalent chromium ions, which is different from at least one corrosion inhibitor, and (iii) at least one corrosion inhibitor, (A) One or more unsubstituted or substituted (preferably substituted) azole compounds and / or salts thereof, with a total concentration of less than 10 mg / L based on the total volume of the passivation composition. Furthermore / or (preferably or) (B) Based on the total volume of the passivation composition, one or more unsubstituted or substituted aliphatic organic acids and / or salts thereof having at least one mercapto group, in a total concentration ranging from 0.1 mg / L to 100 mg / L. At least one type of corrosion inhibitor, A process that includes, (c) A step of bringing a zinc or zinc-nickel coated substrate into contact with the passivation composition so that a chromium-containing passivation layer is deposited on the zinc or zinc-nickel coated substrate. Includes.

[0067] Preferably, the foregoing relating to the passivation compositions of the present invention (those designated as particularly preferred) also applies to the methods of the present invention.

[0068] The method of the present invention in which step (c) is performed without passing an electric current is most preferred.

[0069] In step (a), the method of the present invention is preferable in which the zinc or zinc-nickel coated substrate is a metal screw, a metal nut, a metal clamp, and / or a metal spring.

[0070] The method of the present invention is preferable in which step (c) is carried out at a temperature in the range of 20°C to 50°C and / or for a duration of 10 seconds to 180 seconds.

[0071] When temperatures significantly exceed 50°C, undesirable water evaporation may be observed, along with undesirable energy consumption. When temperatures fall significantly below 20°C, the deposition of the chromium-containing passivation layer is often insufficient, thereby compromising the quality of corrosion protection.

[0072] If the time is significantly less than 10 seconds, the deposition of the chromium-containing passivation layer is often insufficient, which impairs the quality of corrosion protection.

[0073] The method of the present invention is preferable in which step (c) is performed for a time of 20 to 170 seconds, preferably 30 to 150 seconds, more preferably 40 to 110 seconds, and even more preferably 50 to 90 seconds.

[0074] The method of the present invention is preferable in which step (c) is carried out at a temperature in the range of 21°C to 45°C, preferably 22°C to 40°C, and more preferably 23°C to 35°C. Such a moderate temperature enables the sustainable implementation of the method of the present invention.

[0075] By carrying out step (c) within a preferred temperature range and for a preferred time, a particularly advantageous deposition rate can be obtained.

[0076] The method of the present invention is preferable in which the concentration of iron ions in the passivation composition after step (c) is 200 mg / L or less, preferably 100 mg / L or less, most preferably 200 mg / L or less, and most preferably 100 mg / L or less after each step (c), based on the total volume of the passivation composition after each step (c).

[0077] The method of the present invention is more preferable in which, after step (c), the concentration of iron ions in the passivation composition is 500 mg / L or less, preferably 400 mg / L or less, more preferably 300 mg / L or less, most preferably 250 mg / L or less, and even more preferably 200 mg / L or less, based on the total volume of the passivation composition, provided that the passivation composition contains zinc ions at a concentration of 15 g / L or less.

[0078] The method of the present invention is even more preferable in which, after step (c), the concentration of iron ions in the passivation composition is 500 mg / L or less, preferably 400 mg / L or less, more preferably 300 mg / L or less, most preferably 250 mg / L or less, and most preferably 200 mg / L or less, based on the total volume of the passivation composition, provided that the passivation composition contains zinc ions at a concentration of 10 g / L or less.

[0079] After step (c), (d) An additional step of heat-treating a substrate coated with zinc or zinc-nickel, The present invention method, which includes the above, is preferred.

[0080] In many cases, the material is improved by heat treatment to minimize hydrogen embrittlement.

[0081] In step (d), the heat treatment is preferably carried out at a temperature in the range of 150°C to 230°C, more preferably 180°C to 210°C, according to the method of the present invention.

[0082] In step (d), the heat treatment is preferably performed for 1 to 10 hours, more preferably 2 to 8 hours, and most preferably 2.5 to 5 hours, according to the method of the present invention.

[0083] The method of the present invention is preferable in which, after step (c) and / or (d), the formation of white rust by DIN 9227 on the zinc or zinc-nickel coated substrate having a chromium-containing passivation layer is 1% or less. A white rust formation of 1% or less by DIN 9227 serves as a particularly good criterion for demonstrating the excellent corrosion resistance obtained by the method of the present invention.

[0084] The method of the present invention is preferable in which the base material includes iron, more preferably steel.

[0085] In some cases, the method of the present invention is preferred in which the substrate coated with zinc or zinc-nickel is a substrate coated with zinc-nickel. In other cases, the method of the present invention is preferred in which the substrate coated with zinc or zinc-nickel is a substrate coated with zinc.

[0086] In some cases, after step (c) or (d), (e) An additional step of sealing a zinc or zinc-nickel coated substrate with a chromium-containing passivation layer obtained after step (c) or (d), respectively, to obtain a passivated zinc or zinc-nickel coated substrate having a sealing layer, The present invention method, which includes the above, is preferred.

[0087] The method of the present invention is preferable in which the sealing layer comprises one or more compounds selected from the group consisting of inorganic silicates (preferably as particles), silanes, organic polymers, and mixtures thereof.

[0088] With respect to the inorganic silicates (preferably as particles) mentioned above, instead of or in addition to such particles, they are preferably included in the passivation composition of the present invention to enhance corrosion resistance.

[0089] The method of the present invention is preferable in which, after step (c), the chromium-containing passivation layer has a layer thickness in the range of 1 nm to 1200 nm, preferably 10 nm to 1000 nm, more preferably 15 nm to 800 nm, and most preferably 20 nm to 500 nm.

[0090] A further preference of the present invention is that, after step (c), the chromium-containing passivation layer is blue (or at least bluish in color) and has a layer thickness in the range of 30 nm to 150 nm, preferably 40 nm to 140 nm, more preferably 45 nm to 130 nm, most preferably 50 nm to 120 nm, and even more preferably 55 nm to 90 nm.

[0091] In some cases, the method of the present invention is preferred, wherein after step (c), the chromium-containing passivation layer is iridescent and has a layer thickness in the range of 155 nm to 1200 nm, preferably 170 nm to 1000 nm, more preferably 190 nm to 800 nm, and most preferably 200 nm to 600 nm.

[0092] In some cases, the method of the present invention is preferred such that, after step (c), the chromium-containing passivation layer is transparent or yellow and has a layer thickness in the range of 1 nm to 25 nm, preferably 3 nm to 22 nm, more preferably 5 nm to 20 nm, and most preferably 8 nm to 18 nm.

[0093] A third aspect of the present invention provides a zinc or zinc-nickel coated substrate having a chromium-containing passivation layer on top, obtained by the deposition method according to the second aspect.

[0094] Preferably, the foregoing applies to the passivation composition of the present invention (particularly preferred passivation composition), and most preferably to the method of the present invention (particularly preferred method), and similarly to a zinc or zinc-nickel coated substrate having a chromium-containing passivation layer on top of it according to the present invention.

[0095] The present invention will be described in more detail by the following non-limiting embodiments.

[0096] Examples 1. Experiment Group 1 In the first experiment, aqueous passivation compositions for testing were prepared, numbered as shown in Table 1, containing approximately 2 g / L of trivalent chromium ions, cobalt ions, a dicarboxylic acid as a complexing agent, and 3-mercaptotriazole (3-MTA) as a corrosion inhibitor, with a pH of 2.2.

[0097] The method of the present invention was carried out as follows: A zinc-coated iron screw (M8×60) was pretreated as a substrate, and then passedivated for 30 seconds in each aqueous test passivation composition (2 L each) at room temperature (approximately 20°C). After that, the passivated screws were optically inspected and subjected to an NSS test (24 hours).

[0098] Table 1 provides detailed information regarding the passivation composition and the results obtained after passivation.

[0099] [Table 1]

[0100] In Table 1, the meanings of the abbreviations are as follows: "ht" indicates heat treatment of the passivated substrate, "-" indicates no heat treatment, and "+" indicates heat treatment at 210°C for 4 hours; "NSST" represents a neutral salt spray test in accordance with DIN 9227, with a holding time of 24 hours or less than 1% white rust formation. "+" indicates that the test met very well with no rust formation, "0" indicates still acceptable white rust formation, and "-" indicates significantly more than 1% white rust. "Color" refers to the optical appearance of the substrate after passivation; "+" represents blue, and "-" represents transparent or any other color other than blue.

[0101] Experiments 1 and 2 are examples of the present invention, while experiments C1 to C12 are comparative examples. Very similar results were obtained with an immersion time of 50 seconds and a pH of 2.5 (data not shown).

[0102] In this first set of experiments, no iron ions were present in the aqueous passivation composition (i.e., they were not actively added and were not expected in the composition due to short-term use). Typically, such iron ions adversely affect the corrosion resistance of each coated substrate, for example, in the NSS test. Experiments 1 and 2, as well as C1-C12, clearly demonstrate how corrosion resistance is affected in the presence of various concentrations of 3-MTA, with experiments 1 and 2 showing optimal corrosion resistance of the substrate and the blue color of the passivation layer.

[0103] Because iron ions were absent, comparative examples C11 and C12 showed excellent results even without the presence of 3-MTA. Comparative examples C11 and C12 represent an ideal scenario where no corrosion inhibitors are needed because iron ion contamination is absent or not expected. However, such an ideal scenario does not generally represent the everyday situation in which increased iron ion contamination is present or at least expected.

[0104] As shown in the second set of experiments below, 3-MTA is a corrosion inhibitor that works well in the presence of iron ions. However, as shown in Table 1, Examples 1 and 2 show that only relatively low concentrations of 3-MTA are acceptable to maintain the excellent corrosion resistance of the substrate and the blue color of the passivation layer. This result is comparable to Comparative Examples C11 and C12, which do not contain a corrosion inhibitor. As clearly shown from Comparative Examples C1 to C10, concentrations of 3-MTA ranging from 25 mg / L to 500 mg / L adversely affect the corrosion resistance of each substrate (see the "NSST" column, which is "0" and even "-"), and also result in a clear passivation layer or a passivation layer that is not blue.

[0105] 2.2nd experiment In the second experiment, the aqueous test passivation composition had the same basic composition as the test passivation composition in the first experiment. However, in the second experiment, iron ions were added as follows: In the first step, 100 ml of each aqueous test passivation composition was prepared in separate beakers without iron ions. The pH was adjusted to 2.5.

[0106] In the second step, iron substrates (3.5 cm x 5.0 cm iron plates) were placed in each beaker for 2 hours to dissolve iron ions in each aqueous test passivation composition. The dissolution of iron was affected by the presence of 3-MTA in the passivation composition. Subsequently, the concentration of free iron ions was determined by gravimetric analysis. Details and results are summarized in Table 2.

[0107] [Table 2]

[0108] As shown in Table 2, 3-MTA is a properly functioning corrosion inhibitor that actively prevents the release of iron ions from iron-containing substrates. In the absence of 3-MTA (Comparative Example C15), 0.13 g / L of iron ions was measured. However, in the presence of only 7 mg / L (Example 3), the release of iron ions was significantly reduced, and this did not improve further with increasing the amount of 3-MTA (Comparative Examples C13 and C14). Furthermore, the dissolution of the iron substrate and the release of iron ions, respectively, were greatly affected by pH (Comparative Example C15).

[0109] While 3-MTA at concentrations of 25 and 100 mg / L, respectively, adequately prevented the release of iron ions (Comparative Examples C13 and C14), Table 1 clearly shows that such concentrations adversely affected the corrosion resistance of the respective passivated substrates (Comparative Examples C1, C2, C5, and C6 of the first set of experiments).

[0110] Very similar results and conclusions were obtained for 5-mercapto-1-methyltetrazole (data not shown).

[0111] 3.3 Experiment In the third set of experiments, the aqueous test passivation composition was prepared similarly to the test passivation composition in the first set of experiments, except that 3-mercaptopropionic acid (3-MPA) was used instead of 3-MTA. In each of the series of NSS tests, corrosion resistance was not impaired (i.e., "+" NSST) until the concentration of 3-MPA reached approximately 60 mg / L, and was only slightly impaired (i.e., "0" NSST) until the concentration of 3-MPA reached approximately 100 mg / L. Significantly above 100 mg / L, acceptable corrosion resistance was not achieved (i.e., "-" NSST). Therefore, 3-MPA offers a wider range of action than 3-MTA in terms of concentrations at which it can be used without significantly reducing corrosion resistance.

[0112] Furthermore, 3-MPA was additionally tested using the same method as in the second experiment where 3-MTA was tested. Details and results are summarized in Table 3.

[0113] [Table 3]

[0114] Examples 4 and 5, and Comparative Example C16, very effectively prevent the release of iron ions even at high concentrations of 3-MPA. However, our own experiments have shown that acceptable corrosion resistance cannot be obtained when the 3-MPA concentration significantly exceeds 100 mg / L. Nevertheless, excellent acceptable results are obtained within the effective range of 3-MPA concentrations of 100 mg / L or less, preferably 50 mg / L or less.

[0115] In all cases, the series of experiments showed that, in the presence of a corrosion inhibitor, each passivation composition could withstand an iron ion concentration of approximately 250 mg / L.

Claims

1. A passivation composition for depositing a chromium-containing passivation layer on a substrate coated with zinc or zinc-nickel, (i) Trivalent chromium ions, (ii) at least one complexing agent for trivalent chromium ions, distinct from at least one corrosion inhibitor, and (iii) at least one type of corrosion inhibitor, (A) One or more substituted azole compounds and / or salts thereof, with a total concentration of less than 10 mg / L based on the total volume of the passivation composition. and / or (B) One or more unsubstituted or substituted aliphatic organic acids and / or salts thereof having at least one mercapto group, with a total concentration in the range of 0.001 mg / L to 100 mg / L based on the total volume of the passivation composition. At least one type of corrosion inhibitor, A passivation composition containing the following:

2. The passivation composition according to claim 1, wherein one or more substituted azole compounds and / or salts thereof contain one or more substituents selected from the group consisting of amino, nitro, carboxy, hydroxy, sulfonate, and thiol, preferably the substituent being a thiol group.

3. The passivation composition according to claim 1 or 2, wherein one or more unsubstituted or substituted azole compounds and / or salts thereof are selected from the group consisting of monoazoles, diazoles, triazoles, and tetrazoles, preferably diazoles and triazoles, and most preferably triazoles.

4. The passivation composition according to any one of claims 1 to 3, wherein one or more unsubstituted or substituted azole compounds and / or salts thereof are selected from the group consisting of 1,2,4-triazoles.

5. The passivation composition according to any one of claims 1 to 4, wherein one or more substituted azole compounds and / or salts thereof comprise at least mercaptotriazole, preferably at least 3-mercapto-1,2,4-triazole.

6. The passivation composition according to any one of claims 1 to 5, wherein at least one corrosion inhibitor (A) has a total concentration in the range of 0.0001 mg / L to 9.9999 mg / L, preferably 0.01 mg / L to 9.9 mg / L, more preferably 0.1 mg / L to 9.8 mg / L, even more preferably 0.5 mg / L to 9.7 mg / L, even more preferably 1.0 mg / L to 9.6 mg / L, most preferably 2.0 mg / L to 9.5 mg / L, and most preferably 3.0 mg / L to 9.4 mg / L, based on the total volume of the passivation composition.

7. The passivation composition according to any one of claims 1 to 6, wherein the one or more unsubstituted or substituted aliphatic organic acids and / or salts thereof having at least one mercapto group comprises 3-mercaptopropionic acid and / or a salt thereof.

8. The passivation composition according to any one of claims 1 to 7, wherein at least one corrosion inhibitor (B) has a total concentration of 0.01 mg / L to 90 mg / L, preferably 0.1 mg / L to 80 mg / L, more preferably 1 mg / L to 50 mg / L, even more preferably 2 mg / L to 35 mg / L, and most preferably 3 mg / L to 20 mg / L, based on the total volume of the passivation composition.

9. The passivation composition according to any one of claims 1 to 8, wherein at least one complexing agent for the trivalent chromium ion is selected from the group consisting of monocarboxylic acids, dicarboxylic acids, salts thereof, halogen ions, and mixtures thereof, and preferably comprises at least one dicarboxylic acid.

10. The passivation composition according to any one of claims 1 to 9, wherein at least one complexing agent for the trivalent chromium ion is selected from the group consisting of unsubstituted monocarboxylic acids, hydroxyl-substituted monocarboxylic acids, amino-substituted monocarboxylic acids, unsubstituted dicarboxylic acids, hydroxyl-substituted dicarboxylic acids, amino-substituted dicarboxylic acids, salts thereof, halogen ions, and mixtures thereof, preferably comprising at least one dicarboxylic acid.

11. The passivation composition according to any one of claims 1 to 10, wherein the complexing agent for the trivalent chromium ions has a total concentration of 1.0% to 15.0% by weight, preferably 2.0% to 14.0% by weight, more preferably 3.0% to 13.0% by weight, even more preferably 4.0% to 12.0% by weight, and most preferably 5.0% to 11.0% by weight, based on the total weight of the passivation composition.

12. (v) Iron ions with a total concentration of 0 mg / L to 500 mg / L, preferably 0 mg / L to 400 mg / L, more preferably 0 mg / L to 300 mg / L, most preferably 0 mg / L to 250 mg / L, and even more preferably 0 mg / L to 200 mg / L, based on the total volume of the passivation composition. The passivation composition according to any one of claims 1 to 11, further comprising the above.

13. A method for depositing a chromium-containing passivation layer on a substrate coated with zinc or zinc-nickel, (a) A step of preparing a substrate coated with zinc or zinc-nickel, (b) A step of preparing a passivation composition for depositing a chromium-containing passivation layer on a zinc or zinc-nickel coated substrate, wherein the composition is (i) Trivalent chromium ions, (ii) at least one complexing agent for trivalent chromium ions, distinct from at least one corrosion inhibitor, and (iii) at least one type of corrosion inhibitor, (A) One or more substituted azole compounds and / or salts thereof, with a total concentration of less than 10 mg / L based on the total volume of the passivation composition. and / or (B) One or more unsubstituted or substituted aliphatic organic acids and / or salts thereof having at least one mercapto group, with a total concentration in the range of 0.1 mg / L to 100 mg / L based on the total volume of the passivation composition. At least one type of corrosion inhibitor, A process that includes, (c) A step of bringing the zinc or zinc-nickel coated substrate into contact with the passivation composition so that the chromium-containing passivation layer is deposited on the zinc or zinc-nickel coated substrate, A method that includes this.

14. The method according to claim 13, wherein step (c) is performed at a temperature in the range of 20°C to 50°C, and / or step (c) is performed for a time of 10 seconds to 180 seconds.

15. A zinc or zinc-nickel coated substrate having a chromium-containing passivation layer on top, obtained by the deposition method according to claim 13 or 14.

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