EP2309027B1 - Treatment solution for generating chrome and cobalt-free black conversion coatings - Google Patents

Abstract

Treatment solution for producing black chromium- and cobalt-free conversion layers, comprises: (a) at least one complex, water-soluble metal cation selected from oxo cations of the formula M' cd +>, and/or complex halogen ions of the formula M''X ab ->; (b) at least one oxidant; and (c) at least one organic sulfur compound. Treatment solution for producing black chromium- and cobalt-free conversion layers, comprises: (a) at least one complex, water-soluble metal cation selected from oxo cations of the formula M' cd +>, and/or complex halogen ions of the formula M''X ab ->; (b) at least one oxidant; and (c) at least one organic sulfur compound selected from compounds of the Formula 1: HS-R 1>-COOR 2>, and Formula 2: R 5>OOC-R 3>-S-S-R 4>-COOR 6>. c : an integer from 1-3; d : an integer from 1-3; X : selected from F, Cl, Br and I; a : an integer from 3-6; b : an integer from 1-4; and M' and M'' : selected from Mn, V, Ti, W, Mo, Zr, B, Si and Al. R 1> : selected from 1-8C-alkyl, linear and branched, and aryl; R 2> : selected from H, NH 4 +>, Li +>, Na +>, K +>and 1-4C-alkyl, linear and branched; R 3>and R 4> : selected independently from 1-8C-alkyl, linear and branched and aryl; and R 5>and R 6> : selected independently from H, NH4 4 +>, Li +>, Na +>, and 1-4C-alkyl, linear and branched.

Description

Background of the invention

To protect metallic material surfaces from corrosive environmental influences, different methods are available in the prior art. The coating of the metallic workpiece to be protected with a coating of another metal, for example zinc and its alloys, is a widely used and established method in the art. In order to reduce the corrosion of the coating metal or to prevent as long as possible, so-called conversion layers are often used especially on cathodically protective base coating metals such as zinc and its alloys. These are reaction products of the base metal or its alloy with the reaction solution which are insoluble in aqueous media over a wide pH range. Examples of these so-called conversion layers are phosphating and chromating.

In the case of chromating, the surface to be treated is dipped in an acidic solution containing chromium (VI) ions. For example, if it is a zinc surface, some of the zinc will dissolve. Under the reducing conditions prevailing here, chromium (VI) is reduced to chromium (III), which in the surface film which is more alkaline, inter alia, by the evolution of hydrogen is, inter alia, chromium (III) hydroxide or sparingly soluble μ-oxo or μ-hydroxo bridged chromium (III) complex is deposited. In parallel, sparingly soluble zinc chromate (VI) is formed. Overall, a tightly closed, very well protected against the corrosion attack by electrolytes conversion layer on the zinc surface.

In addition to their acute toxicity, chromium (VI) compounds are distinguished by their high carcinogenic potential, so that it is necessary to replace the processes associated with these compounds.

As a substitute for chromating processes with hexavalent chromium compounds, a large number of processes have now been established which use different complexes of trivalent chromium compounds.

As an alternative to processes based on trivalent chromium compounds, the prior art also describes processes which rely on other metals to form a conversion layer. In the application WO 2008/119675 describe treatment solutions for the generation of chromium- and cobalt-free conversion layers containing oxo cations and halogen complex ions, which lead to colorless and slightly iridescent layers.

However, a disadvantage of these chrome and cobalt-free conversion layers described in the prior art is that they hitherto exist only in colors which are based on interference phenomena. This includes almost transparent, bluish or colorfully iridescent and yellowish layers.

Dyes, which are also used in Cr (III) -based passivations, can in principle also be used in chromium-free conversion layers.

However, as in the case of the Cr (III) -based conversion layers, it is not possible here, owing to the small layer thickness (≦ 500 nm), to produce a sufficient absorption of the light reflected by the surface over all wavelengths of the visible light which would be perceived as a black color impression ,

In black-colored processes based on Cr (III) -containing conversion layers is usually a transition metal such as cobalt or iron as Co (II) or Fe (II) or Fe (III) is added to the passivation to produce in situ finely divided black pigments in the conversion layer.

Treatment solutions for producing such black passivations are described, for example, in the document EP 1 970 470 A1 described. Such treatment solutions contain, in addition to Cr ³⁺ and Co ²⁺ ions, nitrate ions and at least two different carboxylic acids.

Iron has the disadvantage that the corrosion protection of the system is significantly weakened by the incorporation of iron-containing pigments.

Although Cobalt allows systems with better conversion protection, but has the disadvantage under certain conditions to be health-harmless.

The patent JP 2005-206872 describes a Cr ⁶⁺ ion-free treatment solution for producing black passivations which, in addition to Cr ³⁺ ions, contains at least one further ion selected from the group consisting of sulfate, chloride, ions of the oxo acids of chlorine and nitrate, and a sulfur compound. The black conversion layers thus produced contain chromium ions.

The font JP 2005-187925 describes processing solutions for the preparation of colored passivation layers containing Cr ³⁺ ions, other metal ions and an organic sulfur compound. The black conversion layers thus produced contain chromium ions.

The font JP 2005-187838 also describes aqueous treatment solutions to produce black colored passivation layers containing ions at least one of Ni and Co and a sulfur compound. The black conversion layers thus formed contain nickel and / or cobalt ions.

Object of the invention

The invention has for its object to provide reaction solutions and methods for increasing the corrosion protection and blackening zinkhaltiger surfaces available, which are free of toxic metals such as chromium and cobalt.

A method that combines the ecological and occupational medical advantage of a chromium and cobalt-free passivation with a decorative high-quality black color impression is therefore desirable.

Description of the invention

The invention is based on the use of sulfur-containing compounds in a chromium ion and cobalt ion-free, aqueous, acidic matrix. With such treatment solutions, black colored conversion layers can be produced on zinc and its alloys.

1. a) mindestens ein komplexes, wasserlösliches Metall-Kation ausgewählt aus der Gruppe umfassend Oxo-Kationen der Formel M'O_c ^d+, wobei c eine ganze Zahl von 1 bis 3 und d eine ganze Zahl von 1 bis 3 ist und /oder Halogen-Komplexion der Formel M"X_a ^b-, wobei X ausgewählt ist aus der Gruppe umfassend F, Cl, Br und I, a eine ganze Zahl von 3 bis 6 ist, eine ganze Zahl von 1 bis 4 ist und M' und M" ausgewählt sind aus der Gruppe umfassend Mn, V, Ti, W, Mo, Zr, B, Si und Al;
2. b) mindestens ein Oxidationsmittel, ausgewählt aus der Gruppe, umfassend Wasserstoffperoxid, organische Peroxide, Alkalimetallperoxide, Perborate, Persulfate, Nitrate, organische Nitroverbindungen, organische N-Oxide und Gemische davon;
3. c) mindestens eine organische Schwefelverbindung, ausgewählt aus der Gruppe, umfassend Verbindungen der Formeln (1) und (2)
   
   
   • wobei R¹ ausgewählt ist aus C1-C8-Alkyl, linear und verzweigt, Aryl, bevorzugt ist C1-C2-Alkyl;
   • R² ausgewählt ist aus H, einem geeigneten Kation (NH₄ ⁺, Li⁺, Na⁺, K⁺) und C1-C4-Alkyl, linear und verzweigt;
   • R³ und R⁴ unabhängig voneinander ausgewählt sind aus C1-C8-Alkyl, linear und verzweigt, Aryl, besonders bevorzugt sind die Reste R³ und R⁴ gleich und C1-C2-Alkyl; und
   • R⁵ und R⁶ unabhängig voneinander ausgewählt sind aus H, einem geeigneten Kation (NH₄ ⁺, Li⁺, Na⁺, K⁺) und C1-C4-Alkyl, linear und verzweigt, bevorzugt sind die Reste R⁵ und R⁶ gleich.

The treatment solutions according to the invention contain

1. a) at least one complex, water-soluble metal cation selected from the group comprising oxo cations of the formula M'O _c ^{d +} , where c is an integer from 1 to 3 and d is an integer from 1 to 3 and / or halogen Complexion of the formula M "X _a ^b- , wherein X is selected from the group comprising F, Cl, Br and I, a is an integer from 3 to 6, is an integer from 1 to 4 and M 'and M" are selected from the group comprising Mn, V, Ti, W, Mo, Zr, B, Si and Al;
2. b) at least one oxidizing agent selected from the group comprising hydrogen peroxide, organic peroxides, alkali metal peroxides, perborates, persulfates, nitrates, organic nitro compounds, organic N-oxides and mixtures thereof;
3. c) at least one organic sulfur compound selected from the group comprising compounds of the formulas (1) and (2)
   
   
   • wherein R ^{1 is} selected from C ¹ -C 8 alkyl, linear and branched, aryl, preferred is C ¹ -C ² alkyl;
   • R ^{2 is} selected from H, a suitable cation (NH ₄ ⁺ , Li ⁺ , Na ⁺ , K ⁺ ) and C ¹ -C ₄ alkyl, linear and branched;
   • R ³ and R ^{4 are} independently selected from C ¹ -C 8 -alkyl, linear and branched, aryl, more preferably R ³ and R ^{4 are the} same and C ¹ -C ² -alkyl; and
   • R ⁵ and R ^{6 are} independently selected from H, a suitable cation (NH ₄ ⁺ , Li ⁺ , Na ⁺ , K ⁺ ) and C ¹ -C ₄ -alkyl, linear and branched, preferably R ⁵ and R ^{6 are the} same ,

By adding suitable sulfur compounds according to the formulas (1) and (2), blackening of the conversion layer is achieved even in the absence of chromium, iron, cobalt and nickel. The list of the resulting compounds is incomplete and includes in particular those compounds which are suitable by hydrolysis or the like under the conditions of the solutions used for the reaction solution or under the conditions of the reaction solution or the reaction with the metal surface Formulas can release corresponding compounds such as the salts and esters of these compounds. The most preferred sulfur compounds are thioglycolic acid, 3-thiopropionic acid, dithiodiglycolic acid and thiolactic acid.

The sulfur compounds of the formula (1) and (2) are added to the treatment solution of the present invention in an amount of 0.2 g / L to 500 g / L, preferably 1 g / L to 100 g / L, and most preferably 3 g / L to 20 g / l added.

The oxo cations of the formula M'O _c ^{d +} are preferably added in the form of their nitrates, sulfates and halides to the treatment solution according to the invention, from which the oxo cations form by hydrolysis in the treatment solution. For example, zirconyl sulfate (ZrO (SO ₄ )) is used as the source of ZrO ²⁺ .

Examples of suitable metals M 'are Mn, V, W, Mo, Ti and Zr. Examples of suitable oxo-cations are MnO ^+, VO ^3+, VO ^2+, WO ₂ ^2+, MoO ₂ ^2+, TiO ^2+, ZrO ^2+, and mixtures thereof. Particularly preferred oxo cations are those of titanium and zirconium. The oxo cations are added to the treating solution in an amount of 0.02 g / L to 50 g / L, preferably 0.05 g / L to 10 g / L, and most preferably 0.1 g / L to 5 g / L.

The halogen complex ions of the formula M "X _a ^b - be in the form of their metal salts, preferably their alkali metal salts, more preferably their sodium and potassium salts are added, the halogen complex of the formula M are preferred." X _a ^b, consisting of A group comprising BF ₄ ^- , TiF ₆ ² - ZrF ₆ ^2- , SiF ₆ ^2- , AlF ₆ ^3- , and mixtures thereof are selected. Particularly preferred are the halogen complex ions SiF ₆ ^2- , TiF ₆ ^2- and ZrF ₆ ^2- . The halogen complex anions of the formula M "X _a ^b" are added to the treatment solution according to the invention in an amount of 0.02 g / l to 100 g / l, preferably 0.05 g / l to 50 g / l and most preferably 0.1 g / l to 10 g / l added.

The treatment solution according to the invention can either contain at least one oxo cation of the formula M'O _c ^{d +} with M ^' equal to Mn, V, Ti, W, Mo, Zr or at least one halogen complex ion of the formula M ^" X _a ^b In another embodiment of the invention, the treatment solution contains a mixture of both at least one oxo cation and at least one halogen complex ion. This embodiment is preferred because it results in increased corrosion resistance of the metal layer (see Examples 3 to 7).

The at least one oxidizing agent in the treatment solution according to the invention is selected from the group comprising hydrogen peroxide, organic peroxides, alkali metal peroxides, persulfates, perborates, nitrates and mixtures thereof. The most preferred oxidizing agent is hydrogen peroxide. The at least one oxidizing agent is added to the treating solution in an amount of 0.2 g / L to 100 g / L, preferably 1 g / L to 50 g / L, and most preferably 5 g / L to 30 g / L.

In a further preferred embodiment of the treatment solution according to the invention, the pH is adjusted by means of an acid or base to a value in the range from 0.5 to 5.0, preferably in the range from 1.0 to 3.0, particularly preferably in the range from 1.3 to 2.0. As the preferred acid, HNO ₃ or H ₂ SO _{4 is used} as the preferred base sodium hydroxide solution.

The application of the treatment solution according to the invention for the production of anticorrosive coatings takes place by direct treatment of the metal surfaces with the treatment solution, by immersing or pivoting the substrate to be coated in or with the treatment solution. Application by dipping or panning is preferably carried out at a temperature of the treating solution in the range of 20 to 100 ° C, preferably 30 to 70 ° C, more preferably 40 to 60 ° C, and most preferably about 50 ° C. The most suitable treatment time for the preparation of anticorrosive coatings by immersion or pivoting of the substrate to be coated in or with the treatment solution varies depending on various parameters, such. Example, the composition of the treatment solution, the treatment temperature, the type of metal surface and the degree of corrosion protection desired and can be determined by routine experimentation. In general, the treatment time is in the range of 5 to 180 s, preferably in the range of 30 to 120 s.

The thus deposited black conversion layers already produce a good corrosion protection with respect to the formation of zinc corrosion products on zinc-containing surfaces.

In order to further increase the corrosion protection of the black conversion layers produced, the described conversion layers can be subjected to conventional aftertreatment processes. This includes, for example, seals based on silicates, organofunctional silanes and nanoscale SiO ₂ , and polymer dispersions.

The sealing layers produced by the subsequent treatment improve the barrier effect of the underlying conversion layer and thus additionally improve the corrosion protection of the entire coating system.

Examples Comparative example

800 ml of a solution of 0.25 wt .-% zirconyl sulfate is added with stirring with 13.6 g / l potassium hexafluorotitanate and stirred vigorously for 30 min. The solution is then made up to 1000 ml. The solution is diluted 1: 4 with water (1 L solution + 3 L water) and then 1 L of a hydrogen peroxide solution (10 wt%) added.

The pH is adjusted to pH 1.6 at 50 ° C. with NaOH.

A sheet of low-alloy steel is, after suitable pretreatment in an alkaline galvanizing electrolyte (Protolux® 3000, a product of Atotech Deutschland GmbH, containing 12 g / l zinc and 120 g / l NaOH) coated with 10 microns zinc.

The sheet is rinsed after galvanizing and dipped directly into the above prepared treatment solution. After 60 s treatment time with slight movement the sheet is removed, rinsed and dried. It has a multicolored iridescent surface.

Embodiment 1

A treatment solution for producing conversion layers as described in Comparative Example 1 is mixed with 10 g / l of thioglycolic acid and the pH is adjusted to pH 1.6 (50 ° C.) with NaOH.

A sheet of low-alloy steel is coated after appropriate pretreatment in an alkaline galvanizing electrolyte (Protolux® 3000, a product of Atotech Deutschland GmbH, containing 12 g / l zinc and 120 g / l NaOH) with 8-15 microns zinc.

The sheet is rinsed after galvanizing and dipped directly into the treatment solution prepared above. After 60 s treatment time with slight movement, the sheet is removed, rinsed and dried. It has a deep black surface.

Embodiment 2

A treatment solution for producing conversion layers as described in Comparative Example 1 is admixed with 11 g / l of 3-thiopropionic acid and the pH is adjusted to pH 1.6 (50 ° C.) with NaOH.

A sheet of low-alloy steel is coated after suitable pretreatment in an alkaline galvanizing electrolyte (Protolux® 3000) with 10 μm zinc.

The sheet is rinsed after galvanizing and dipped directly into the treatment solution prepared above. After 60 s treatment time with slight movement, the sheet is removed, rinsed and dried. It has a deep black surface.

Embodiment 3

A treatment solution for producing conversion layers, as described in Comparative Example 1, is admixed with 11 g / l dithiodiglycolic acid and the pH is adjusted to pH 1.6 (50 ° C.) with NaOH.

A sheet of low-alloy steel is coated after suitable pretreatment in an alkaline galvanizing electrolyte (Protolux® 3000) with 10 μm zinc.

The sheet is rinsed after galvanizing and dipped directly into the treatment solution prepared above. After 60 s treatment time with slight movement, the sheet is removed, rinsed and dried. It has a deep black surface.

The sheet with the surface thus produced is dried at 80 ° C in a convection oven for 15 min and the corrosion protection in the neutral salt spray test according to ISO 9227 NSS tested. The sheet had a life of 48 hours until the appearance of zinc corrosion products> 5% of the area.

Embodiment 4

A sheet with a surface produced according to Embodiment 3 is rinsed, dipped in a sealing solution consisting of a silicate-containing polyurethane dispersion (Corrosil® Plus 501, a product of Atotech Deutschland GmbH) and dried at 80 ° C in a convection oven for 15 min. The corrosion protection tested in the neutral salt spray test according to ISO 9227 NSS. The sheet had a life of 120 h until the appearance of zinc corrosion products> 5% of the area. A sealing solution usually used for increasing the corrosion protection can therefore also be used on the chromium- and cobalt-free black conversion layers according to the invention.

Embodiment 5

A treatment solution for the production of conversion layers as described in Comparative Example 1 is mixed with 13 g / l of thiolactic acid and the pH is adjusted to pH 1.6 (50 ° C.) with NaOH.

A sheet of low-alloy steel is coated after suitable pretreatment in an alkaline galvanizing electrolyte (Protolux® 3000) with 10 μm zinc.

The sheet is rinsed after galvanizing and dipped directly into the treatment solution prepared above. After 60 s treatment time with slight movement, the sheet is removed, rinsed and dried. It has a deep black surface.

The sheet with the surface thus produced is dried at 80 ° C in a convection oven for 15 min and the corrosion protection in the neutral salt spray test according to ISO 9227 NSS tested. The sheet had a life of 48 hours until the appearance of zinc corrosion products> 5% of the area.

Embodiment 6

With stirring, 250 ml of a solution of hydrogen peroxide (10% by weight) are added to 1000 ml of a solution of 3.5 g / l of potassium hexafluorotitanate, and 10 g / l of thioglycolic acid are added.

The pH is adjusted to pH 1.6 at 50 ° C. with HNO ₃ .

A sheet of low-alloy steel is coated after suitable pretreatment in an alkaline galvanizing electrolyte (Protolux® 3000) with 10 μm zinc.

The sheet is rinsed after galvanizing and dipped directly into the treatment solution prepared above. After 60 s treatment time with slight movement the sheet is removed, rinsed and dried. It has a deep black surface.

The sheet with the surface thus produced is dried at 80 ° C in a convection oven for 15 min and the corrosion protection in the neutral salt spray test according to ISO 9227 NSS tested. The sheet had a life of 24 h until the appearance of zinc corrosion products> 5% of the area.

Embodiment 7

With stirring, 250 ml of a solution of hydrogen peroxide (10% by weight) are added to 1000 ml of a solution of 2.5 g / l of zirconyl sulfate, and 10 g / l of thioglycolic acid are added.

The pH is adjusted to pH 1.6 at 50 ° C. with NaOH.

A sheet of low-alloy steel is coated after suitable pretreatment in an alkaline galvanizing electrolyte (Protolux® 3000) with 10 μm zinc.

The sheet is rinsed after galvanizing and dipped directly into the treatment solution prepared above. After 60 s treatment time with slight movement, the sheet is removed, rinsed and dried. It has a deep black surface.

The sheet with the surface thus produced is dried at 80 ° C in a convection oven for 15 min and the corrosion protection in the neutral salt spray test according to ISO 9227 NSS tested. The sheet had a life of 24 h until the appearance of zinc corrosion products> 5% of the area.

Claims (12)

1. Treatment solution for producing black chromium- and cobalt-free conversion layers, comprising

   a) at least one complex, water-soluble metal cation selected from the group consisting of oxo cations of the formula M'O_c ^d+, where c is an integer from 1 to 3 and d is an integer from 1 to 3, and /or complex halogen ions of the formula M"X_a ^b-, where X is selected from the group consisting of F, Cl, Br and I, a is an integer from 3 to 6, b is an integer from 1 to 4 and M' and M" are selected from the group consisting of Mn, V, Ti, W, Mo, Zr, B, Si and Al

   b) at least one oxidant

   c) at least one organic sulphur compound selected from the group consisting of compounds of the formulae (1) and (2)

   

   

   where R¹ is selected from among C1-C8-alkyl, linear and branched, and aryl;

   R² is selected from the group consisting of H, NH₄ ⁺, Li⁺, Na⁺, K⁺ and C1-C4-alkyl, linear and branched;

   R³ and R⁴ are selected independently from the group consisting of C1-C8-alkyl, linear and branched and aryl; and

   R⁵ and R^6, are selected independently from the group consisting of H, NH₄ ⁺, Li⁺, Na⁺, K⁺ and C1-C4-alkyl, linear and branched.
2. Treatment solution according to Claim 1, wherein M' is selected from the group consisting of Mn, V, Ti, W, Mo and Zr.
3. Treatment solution according to Claim 1, wherein M" is selected from the group consisting of B, Al, Si, Ti and Zr.
4. Treatment solution according to any of Claims 1 to 3 which contains at least one oxo cation of the formula M'O_c ^d+ and at least one complex halogen ion of the formula M"X_a ^b- _.
5. Treatment solution according to any of Claims 1 to 4, wherein the oxidant is selected from the group consisting of hydrogen peroxide, organic peroxides, alkali metal peroxides, perborates, persulphates, nitrates, organic nitro compounds and organic N-oxixes and mixtures thereof.
6. Treatment solution according to any of Claims 1 to 5, wherein the radicals of the compounds of the formulae (1) and (2) are selected from among:

   R¹ is C1-C2-alkyl and

   R³ and R⁴ are selected independently from among C1-C2-alkyl.
7. Treatment solution according to Claim 6, wherein R³ and R⁴ are identical.
8. Treatment solution according to any of Claims 1 to 7, wherein the organic sulphur compound is selected from the group consisting of thioglycolic acid, dithiodiglycolic acid, thiolactic acid and 3-thiopropionic acid.
9. Treatment solution according to any of Claims 1 to 8, wherein the oxidant is a peroxide.
10. Treatment solution according to Claim 9, wherein the peroxide is hydrogen peroxide.
11. Treatment solution according to any of Claims 1 to 10, wherein the at least one oxo cation of the formula M'O_c ^d+ is selected from the group consisting of MnO⁺, VO³⁺, VO²⁺, WO₂ ²⁺, MoO₂ ²⁺, TiO²⁺, ZrO²⁺ and mixtures thereof.
12. Treatment solution according to any of Claims 1 to 11, wherein the at least one complex halogen ion of the formula M'X_a ^b- is selected from the group consisting of SiF₆ ^2-, TiF₆ ^2- and ZrF₆ ^2-.