EP2907894A1 - Method for production of a substrate with a chromium VI free and cobalt-free passivation - Google Patents

Abstract

The invention relates to a method for producing a metallic substrate provided with a chromium-VI-free and cobalt-free passivation by applying a first acidic passivation and a second alkaline passivation, comprising a silane-modified and / or siloxane-modified silicate, with which improved corrosion protection is achieved. an aqueous acidic passivating composition; and a passivated substrate and a passivation applying apparatus.

Description

The invention relates to a method for producing a substrate provided with a chromium VI-free and cobalt-free passivation, to the substrate provided with such a passivation and to a device for carrying out the method and with an aqueous acidic passivation composition which are suitable for use in the aforementioned method.

The passivation of metallic substrates has been proven, but components of the passivation solutions have proved to be of concern from a health and environmental point of view. Thus, chromium (VI) compounds are often no longer used and elements such as cobalt and nickel are often no longer desirable.

A chromium (VI) -free and cobalt-free passivation composition is disclosed in U.S. Pat US 4,578,122 disclosed. There are nitrate ions and chromium (III) compounds used in aqueous, acidic solution, wherein additionally activating metal ions, eg. As iron, aluminum, lanthanum or cerium ions are added. The ratio of nitrate ions on the one hand to chromium (III) ions and activating metal ions on the other hand should not be below 4: 1.

The addition of in the US 4,578,122 mentioned, activating metal ions is either no longer desirable for reasons of health or environmental protection in the future or the use of metal ions is complex.

The DE-OS 3 213 384 discloses a first acidic and a second alkaline passivation that is chromium VI free and cobalt free. However, this two-stage passivation has not yet been optimized with regard to corrosion protection.

It is therefore the object of a method for the passivation of metallic substrates which provides good corrosion protection and avoids unnecessary risks to health and the environment. Another object is to propose a composition and a device for the passivation of metallic substrates, which are suitable for carrying out the method.

The object underlying the invention is achieved by a method according to claim 1, an aqueous solution according to claim 21, a substrate according to claim 23 and a device according to claim 30.

In order to produce a metallic substrate provided with a chromium VI-free and cobalt-free passivation, the method according to the invention provides that a first acidic and a second alkaline passivation are applied, wherein an aqueous alkaline composition used for producing the second alkaline passivation contains silane-modified silicates , The combination of the two passivations, acidic and alkaline, provides good corrosion protection.

The first acidic and the second alkaline passivation are applied as aqueous compositions, the composition of which is explained below. The term passivation is used in the context of this invention both for the aqueous composition for passivating the substrate and for applying the aqueous compositions as well as for the coating applied to the surface of the metallic workpiece. Treating the surface of the metallic substrate with the acidic and alkaline aqueous compositions results in the deposition of chemical components contained therein which form a coating on the surface of the substrate, ie, the passivation. The coating or coatings provide improved protection against corrosion.

The first, acidic passivation may be of any composition; However, it is according to the invention preferably chromium-VI-free and cobalt-free. Preferably, it is also nickel-free. A particularly preferred composition for the first, acidic passivation is described below.

The coated with a first acidic passivation substrate or workpiece according to the invention coated with a second passivation, wherein it is in the second Passivation is an alkaline passivation. The corrosion protection is significantly increased by this second alkaline passivation. Workpieces in which the acidic passivation contains no vanadium or tungsten are significantly more resistant to corrosion by a second, alkaline passivation applied to the first, acidic passivation. Specifically, however, corrosion protection is improved when the first acidic passivation is made using an aqueous acidic composition containing vanadium and / or tungsten or their compounds.

An essential feature of the invention is the application of a silicate-containing aqueous composition as a second, alkaline passivation for coating the first acidic passivation. In this way, a silicate compound is applied to the first acidic passivation. Typical silicate compounds are water glasses, but also aqueous polysilicates or colloidal silicates are well suited for the second, alkaline passivation. It is preferred that the second alkaline passivation comprises sodium, potassium, lithium and / or ammonium silicate. A second alkaline passivation may also be applied to the workpiece, which comprises a mixture of silicate compounds. Both colloidal silicates and dissolved silicates can be used. Silane-modified or siloxane-modified silicates, in which silanes or siloxanes are attached to the silicates, preferably polysilicates, have also proven to be suitable for the implementation of the invention. Most silicates form alkaline solutions or suspensions in the presence of water. If necessary, however, by addition of alkalis, z. As sodium hydroxide, the alkalinity can be increased.

The use of lithium polysilicate in the aqueous composition for passivating metallic substrates has proved to be particularly advantageous for producing the second alkaline passivation. The application of an aqueous composition of lithium polysilicate or the mixture of lithium polysilicate with other water glasses (sodium and / or potassium silicate) or colloidal silica sols on the first acidic passivation provides an extremely improved corrosion protection. At the same time, the use of lithium polysilicate for the production of the second alkaline passivation achieves the avoidance of the formation of gray films on the surface of the metallic substrate passivated according to the invention, which is customary for passivations of aqueous compositions with sodium or potassium water glasses. According to the invention, the aqueous alkaline composition used for the second alkaline passivation comprises a silane or siloxane. The addition of the silane or siloxane serves to further increase the corrosion protection. Preferably, a vinyl and / or aminosilane is used to prepare the second alkaline passivation; but are also suitable Expoxysilane and the siloxanes of the above and below mentioned silanes. In particular, alkylalkoxysilanes, in this case mono-, di- or trialkylalkoxysilanes, are suitable, individually or as a mixture in combination with silicates, to build up a corrosion-protecting coating on the metallic workpiece already treated with an acidic aqueous composition. Various silane compounds can be used together in a mixture. Particularly suitable silane compounds are methacryloxymethyltriethoxysilane, methacryloxymethyltriethoxysilane, 3-aminopropylmethyldiethoxy silane, 3-aminopropyltriethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxy silane, 3-glycidyloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, methyltrimethoxysilane, methyltrimethoxysilane and 3-mercaptopropyltrimethoxysilane.

Silane or siloxane can be used in an amount of 1% by weight to 99% by weight based on the total amount of the second alkaline passivation aqueous composition. However, already show aqueous compositions containing only small amounts of silane, z. B. up to 20% by weight, a significantly improved corrosion protection.

According to the invention, an aqueous alkaline composition is used for producing the second alkaline passivation, which comprises both silicates and silanes and / or siloxanes or mixtures of silicates and silanes or siloxanes or compounds of a silicate and a silane component, in the following: silane-modified silicates, or Compounds of a silicate and a siloxane, hereinafter siloxane-modified silicates. The silanes or siloxanes are typically z. B. bound by the hydrolysis as covalent side chains of the silicates or. These silane-modified or siloxane-modified silicates form excellent corrosion protection on a first acidic passivation, which far exceeds the effect of simple acidic or alkaline passivation. The silane-modified or siloxane-modified Silicates are detectable by NMR spectroscopy on the metallic substrate. In particular, silicon-carbon bonds (SiC bonds) can be detected. At the same time, the second alkaline passivation forms an excellent basis for further coatings, eg. As coloring coatings or coatings containing lubricants or other additives that further improve the use of the coated surface. If silane-modified silicates are mentioned or described in connection with this invention, the use of siloxane-modified silicates is always meant and included as well.

The second alkaline passivation can according to a further preferred embodiment of the invention from partially or preferably completely hydrolyzed silicate and silane or. Siloxane compounds be prepared. The common hydrolysis of silicates and silanes or siloxanes in aqueous solution, on the one hand, the formation of silane-modified or siloxane-modified silicates. On the other hand, alcohols released by the factory hydrolysis can be removed, so that users can be supplied with aqueous alkaline compositions which are low in volatile organic compounds (low in VOC) or free from volatile organic compounds (VOC-free). , The liberated by the hydrolysis alcohols can, for example, by ultramembrane filtration or reverse osmosis, but also by distillation, for. B. vacuum distillation can be removed. Typical inventive aqueous alkaline compositions for passivating metallic substrates contain at most 1% by weight of alcohol, preferably at most 0.3% by weight of alcohol.

If desired, it is readily possible to add additives to the aqueous composition for the second alkaline passivation. The additives are usually already added to the liquid composition from which the second alkaline passivation is prepared. They either exert their effect, for example with defoamers or stabilizers, during application or, for example, with lubricants or dyes, after the application and, if appropriate, drying of the second alkaline passivation.

According to an advantageous embodiment of the invention, which is to be regarded as a separate technical solution, is for producing the first acidic passivation of the metallic Substrate proposed to use an aqueous acidic cobalt and chromium (VI) -free composition having a chromium (III) compound, an inorganic acid and optionally a fluorine source, and which is characterized in that the aqueous composition Compound of the metals vanadium or tungsten, said metal compound may be used individually or in admixture with other vanadium or tungsten compounds.

Molybdenum, vanadium and tungsten compounds in combination with the abovementioned, already known constituents of the first acidic passivation already have an excellent corrosion protection, the composition according to the invention both in handling the aqueous composition z. B. during coating but also as finished applied passivation has a significantly reduced risk of health and environmental damage and can be used with high reliability. Molybdenum, vanadium and tungsten compounds are incorporated into the first acidic passivation, where they improve the corrosion protection.

The aqueous acidic and alkaline compositions according to the invention for passivating metallic substrates in general are suitable for all metallic surfaces or substrates, but particularly well for workpieces with a surface made of steel, iron, aluminum or zinc, but especially for workpieces whose surface with an alloy is provided by one or both of the metals aluminum and zinc with other metals. Typically, for example, a suitable zinc-aluminum alloy, an aluminum or a zinc alloy with other metals such. As iron or magnesium, for. As with a zinc-iron alloy, all of which can be provided with a corrosion protection coating. The layer thickness of the applied coating of metal or alloy is between 5 .mu.m and 100 .mu.m. The metallic alloy deposited on a substrate shows up as a discrete layer. A typical application is coil coating, ie the passivation of steel strip.

Advantageously, metal-oxygen compounds of the metals molybdenum, vanadium and / or tungsten are used in the aqueous acidic composition for passivation. Preference is given to one or more of the compounds listed below in the aqueous acidic composition: potassium orthovanadate, potassium metavanadate, sodium orthovanadate, sodium metavanadate, sodium tungstate, sodium paratungstate and vanadium pentoxide, and sodium molybdate and potassium molybdate. According to the invention, compounds of the metals molybdenum, vanadium and / or tungsten are used which dissociate in the aqueous, acidic composition for passivation and thereby release molybdenum, vanadium and / or tungsten ions. Molybdenum, vanadium and tungsten ions are incorporated in the passivation layer and cause the construction of a very good corrosion protection already in the acidic passivation alone.

According to a preferred alternative composition for the passivation of metallic substrate, a phosphonic acid or a mixture of phosphonic acids are used as complexing agents. Particular preference is given to using organic phosphonic acids, for example (1-hydroxyethane-1,1-diyl) biphosphonic acid, 2-phosphonobutanel 1,2,4-tricarboxylic acid, aminotrimethylenephosphonic acid, ethylenediamine tetramethylenephosphonic acid or diethylenetriaminepentamethylenephosphonic acid or mixtures thereof. The use of salts of phosphonic acid may prove advantageous in connection with the invention. Particularly suitable are the phosphonates listed below, each used individually or in admixture: tetrasodium (1-hydroxyethane-1,1-diyl) biphosphonate, trisodium (1-hydroxy-ethane-1,1-diyl) biphosphonate, pentasodium ethylenediamine tetramethylene phosphonate or Heptanatrium-diethylenetriamine. These salts dissociate in the aqueous, acidic passivating composition, so that the phosphonates are available as complexing agents. Phosphonic acids and their derivatives can also be advantageously used in conjunction with vanadium and tungsten compounds in acidic aqueous compositions. Here, the use of phosphonic acid has proved successful as a complexing agent.

In the process of the invention, it is preferred that the acidic aqueous compositions for passivating metallic substrates comprise one or more elements or compounds of the group comprising molybdenum, manganese, cerium and lanthanum. By adding these elements or their compounds, preferably their salts and oxides, a further improvement of the anticorrosive properties of the passivation according to the invention is achieved.

The aqueous acidic passivating composition according to a preferred embodiment of the invention comprises a chromium (III) compound or a mixture of chromium (III) compounds selected from the group consisting of chromium (III) sulphate, Chromium (III) hydroxide, chromium (III) dihydrogen phosphate, chromium (III) chloride, chromium (III) nitrate, sodium chromium (III) sulfate, potassium chromium (III) Sulfate and chromium (III) salts of organic acids. It has been found that an aqueous, acidic passivating composition has good anti-corrosive properties even without the use of a chromium (VI) compound. The chromium (III) compound is used in an amount of at least 0.05 g / l to a maximum of saturation. If the amount falls below 0.005 g / l, no sufficient corrosion protection is built up. Exceeding the saturation is not useful for economic reasons.

It has also proven to be advantageous to add to the acidic aqueous composition for passivation a nitrate compound or a mixture of nitrate compounds. In addition to nitrogen-containing acids such as nitric acid but also salts of these acids are preferably used. Typical salts particularly suitable for use in the passivation composition are salts of the alkali metals, ammonium salts or salts of the metal ions contained in the passivating composition, e.g. For example, chromium (III) nitrate. The nitrogen and chromium (III) compounds described above are present in the aqueous, acidic composition for passivation in substantially dissociated form. The proportion of nitrate compounds is preferably 5% by weight to 20% by weight based on the total composition used for the passivation.

Also advantageous is the use of an aqueous, acidic cobalt and chromium (VI) -free composition for the passivation of metallic substrates containing a chromium (III) compound, an acid, metal ions, nitrate ions and optionally a fluorine source and a phosphonic acid and / or their derivatives and which is characterized in that nitrate ions are used to the sum of chromium and metal ions in a ratio of not more than 3: 1, preferably of at most 1: 3. The reduced nitrate usage proves advantageous in the use of this aqueous acidic passivating composition because fewer nitrous gases are released.

However, it is recommended for the safe application of the coating and the construction of a good corrosion protection that the acidic aqueous composition for passivation to a pH <4, preferably a pH <3 is set. To ensure this, an acid or a mixture of acids is added. Particularly advantageous has been the use of organic and / or inorganic acids, typically one or more of the group consisting of phosphoric acid, hydrochloric acid, nitric acid and / or sulfuric acid as inorganic acids and formic acid, succinic acid, acetic acid, oxalic acid, peracetic acid Salicylic acid and citric acid as organic acids. The organic acids alone do not always ensure that the desired pH is reached, but their addition proves to be expedient because the organic acids also act as complexing agents in the acidic aqueous composition.

In order to effect a good adhesion of the passivation, the aqueous, acidic composition preferably comprises a fluorine source. Such a fluorine source is preferably a compound or mixture of compounds selected from the group comprising hydrofluoric acid, hexafluorotitanic acid, hexafluorozirconic acid, sodium fluoride (NaF), potassium fluoride (KF), ammonium fluoride (NH ₄ F), sodium bifluoride (NaHF ₂ ), potassium bifluoride (KHF ₂ ) and ammonium bifluoride (NH ₄ HF ₂ ). The fluorine compounds used as the fluorine source are used in an amount of 0.1% by weight to 5% by weight based on the aqueous composition. The fluorine compounds are preferably used as technically pure, soluble powders.

It is expressly noted here that the above-described use of elements or compounds, the vanadium, tungsten, molybdenum, manganese, cerium or lanthanum and phosphonic acid and derivatives thereof can be carried out individually or in any desired combination. Aqueous acidic compositions which contain one or more of these elements or compounds cause good corrosion protection even as an acidic passivation alone.

The preferred aqueous, acidic composition for passivating metallic substrates is substantially harmless to health and the Environmentally not or only slightly polluting substances composed. It is free of cobalt, nickel and chromium (VI) compounds. It is also preferably free of peroxide compounds and can be prepared without the use of carboxylic acids. In addition, in preferred embodiments, the use of nitrate compounds is minimized so that the emission of nitrous gases is greatly reduced.

The application of the aqueous, acidic composition for passivation takes place at room temperature, at a maximum at temperatures up to 80 ° C. The metallic substrate is in most cases immersed in a bath of the aqueous acidic and then the aqueous alkaline passivation composition, but the passivating compositions can also be prepared by other conventional and well-known application methods (spraying, dipping, dip-spinning, knife coating, rolling ) are applied to the metallic substrate. The application of the aqueous compositions for passivation is usually carried out with a treatment time which is between 1 second and 180 seconds, preferably about 30 seconds to 120 seconds. The application of the composition for passivation may be followed by drying, which may be carried out at temperatures between room temperature and approximately 250 ° C. Drying is only aimed at removing excess liquid; a reaction, z. Example, a hydrolysis or condensation of the components which form the passivating coating on the metallic substrate is not required.

Optionally, the metallic substrate may be cleaned, in particular degreased, prior to application of the composition for passivation. Aqueous solutions for cleaning and degreasing are known from the prior art.

The first acidic passivation is applied in a layer thickness of 10 nm to 1 μm, preferably in a layer thickness of 20 nm to 500 nm. The second alkaline passivation is applied to a layer thickness of 10 nm to 1 μm, preferably in a layer thickness of 10 nm to 500 nm. These thin layers result from the adhesion of the aqueous solutions on the substrate or on previous passivation layers, a subsequent curing is not required. The layer thickness does not change after application and drying.

The aqueous acidic and alkaline compositions needed to carry out the process of the invention are preferably supplied as a concentrate which is diluted with water for use in a ratio of concentrate: water of from 1: 5 to 1:20, often 1:10. The respective aqueous acidic or alkaline compositions are each offered as one-component products.

According to the invention, the excellent corrosion protection is achieved by first applying an acidic passivation and then an alkaline passivation to the metallic substrate. Accordingly, an analysis of the finished coated substrate shows that, starting from the substrate, first a first passivation layer is detected which comprises chromium and nitrogen and optionally fluorine, vanadium and / or tungsten, alternatively also other metallic or rare earth elements. However, this first passivation layer usually contains no silicon and none of the elements sodium, potassium or lithium. A second passivation layer is applied to this first passivation layer. The second passivation layer is therefore not applied directly to the metallic substrate. Typically, silicon as well as sodium, potassium and / or lithium can be detected in the second passivation layer. However, this second passivation layer typically does not include chromium, fluorine, tungsten, vanadium, or other metallic or rare earth elements. Non-metallic elements such. As carbon, phosphorus or nitrogen may optionally be detected in both passivation layers.

Details of the invention will be explained with reference to the following embodiments:

For all of the examples below, the amounts given are by weight based on the total composition of the particular aqueous composition used to make the passivation. Unless otherwise stated, pure substances (100%) have been used. The preparation of the aqueous, acidic or alkaline composition for passivation is carried out by mixing or dissolving the individual constituents.

The water is in the acidic aqueous composition mainly z. B. by the aqueous chromium (III) salt solution, here a sulfate or a nitrate, introduced into the liquid composition for passivation. Smaller quantities are finally added. These compositions have a pH of 1.5 to 1.8. They can easily be stored for more than six months.

The preparation of the aqueous alkaline composition is typically carried out by adjusting the solids content or proportion of aqueous silicates by adding appropriate amounts of water and - provided so far - by mixing in silanes. If silicates and completely or partially hydrolyzed optionally silanes or siloxanes are used, the hydrolysis is carried out at the factory, so that the ready-to-use products have a reduced alcohol content compared to the unhydrolyzed products or release less alcohol during processing.

By applying the aqueous, acidic composition for passivation by rolling at room temperature on steel sheets having a surface which here z. B. from a zinc-iron alloy, on the metallic substrate generates a passivation layer. The application is effected by a roller arrangement which is passed by the steel sheet. It is then rinsed to remove excess acidic composition. The subsequent drying is carried out here by a drying oven at 150 ° C, which passes through the provided with the first passivation steel sheet within a maximum of 10 minutes. In the same way, the second alkaline coating is produced.

Exemplary embodiments of Tables 1 and 2

It is expressly noted here again that according to the invention any acidic passivations can be applied as the first coating on a metallic substrate. The aqueous acidic compositions detailed herein represent only one possible embodiment for acidic passivation. Tables 1 and 2 show predominantly compositions of an aqueous acidic composition for a first acidic passivation containing vanadium and tungsten compounds.

Chromium (III) sulfate and chromium (III) nitrate are, individually or, as in Experiment 11, also together the major constituent of the passivating composition. When used as a 20% solution, the proportion of the chromium (III) compound in the passivating composition is between 64.0% by weight and 77.2% by weight.

Although a nitrate compound may also be added in the form of chromium (III) nitrate, it is preferred to add, as shown in Tables 1, 2, a nitrate salt, in this case sodium nitrate. The proportion of the nitrate compound is preferably between 13% by weight and 16% by weight, but may also be between 5% by weight and 10% by weight.

As an optional fluorine source, a fluorine salt is preferably used. The statements in Table 1 and 2 are sodium hydrogen difluoride; however, other fluorine compounds named above are also suitable.

The embodiments of the composition according to the invention in Tables 1, 2 show that organic acids can be used individually or in combination. These acids act as complexing agents, but also support a low pH. Essential for the adjustment of the pH, however, is above all the addition of an inorganic acid, preferably nitric acid. Table 1 Acid passivating compositions (chromium (III) sulphate) Trial No: 1 2 3 4 5 Chromium (III) compound Chromium (III) sulfate (20% solution) 77.2% 72.7% 72.2% 64.0% 70.0% nitrate compound sodium nitrate 9.7% 15.8% 15.8% 13.5% 13.5% fluorine compound sodium hydrogen 3.5% 2.8% 2.8% 2.8% 1.2% Organic acid citric acid 2.5% 2.5% 2.5% oxalic acid 2.5% 2.5% Inorganic acid Nitric acid ENT ₃ 3.1% 2.2% 2.2% 2.2% 2.2% Vanadium or tungsten compound sodium vanadate 1.5% 1.5% potassium vanadate vanadyl 15.0% Sodium tungstate Natriumolybdat 0.5% potassium molybdate phosphonic 1-hydroxyethane-1,1-diphosphonic acid 1.5% water 4.0% 2.5% 2.5% 9.1% total 100.0% 100.0% 100.0% 100.0% 100.0%

However, the use of nitric acid is preferred only because it is considered to be an additional source of nitrate ions. The pH of preferably below 4 can also be well with z. As sulfuric acid, hydrochloric acid or phosphoric acid, as well as mixtures of inorganic and / or organic acids are used, see experiments 11,12 in Table 2. Low amounts of up to 5% by weight of inorganic acid are usually sufficient to a Adjust pH <4.

The addition of vanadates and tungstates is carried out in amounts between 0.1% by weight and 5% by weight, preferably in amounts of from 0.5% by weight to 3% by weight. The statements according to Tables 1, 2 show that even small amounts of vanadates or tungstates or mixtures of vanadates and tungstates significantly increase the corrosion protection effect of a passivation composition.

The anticorrosive effect of this first, acidic passivation solution is further enhanced when molybdate or manganates or mixtures of molybdates and manganates are used. Quantities of 0.05% by weight to 3% by weight per molybdenum compound are sufficient to achieve a significant synergy effect in corrosion protection. Preferably, up to 1.5% by weight of molybdate and up to 0.5% by weight of manganates are used.

Furthermore, the addition of phosphonic acids proves to be advantageous. They act as complexing agents. The addition of individual phosphonic acids is already effective. But also the addition of mixtures of different phosphonic acids shows good results. Phosphonic acids are added in amounts of 0.01% to 5% by weight, preferably in amounts of 0.5% to 3% by weight. It is again expressly noted here that the use of elements or compounds, the vanadium, tungsten, molybdenum, manganese, cerium or lanthanum and phosphonic acid and derivatives thereof, each individually or in any compound good corrosion protection properties guaranteed even at a first acidic passivation. Table 2 Acid passivation composition (chromium (III) nitrate and sulfate) Trial No: 6 7 8th 9 10 11 12 Chromium (III) compound proportion of proportion of proportion of proportion of proportion of proportion of proportion of Chromium (III) sulfate solution 20% 5.0% 70.0% Chromium (III) nitrate solution 20% 65.7% 65.7% 65.7% 65.7% 65.7% 65.7% nitrate compound sodium nitrate 15.8% 15.8% 15.8% 15.8% 15.8% 15.8% 15.8% fluorine compound sodium hydrogen 0.2% 0.2% 0.2% 1.7% 1.7% 1.7% 1.7% Organic acid citric acid 1.0% 1.0% 2.5% 2.5% 0.1% 0.1% oxalic acid 2.5% salicylic acid 2.5% Succinic acid 1.0% 1.0% 1.0% 1.0% 1.0% 1.0% Inorganic acid Nitric acid HN03 2.2% 2.2% 2.2% 2.2% 2.2% 1.2% 1.2% sulfuric acid 1.5% 1.5% Vanadium or tungsten compound sodium vanadate potassium vanadate 1.5% vanadyl 1.3% 1.3% Sodium tungstate 1.0% 1.0% 1.0% Natriumolybdat 1.0% 1.0% 1.0% potassium molybdate 0.5% 0.5% 0.5% phosphonic 1-hydroxyethane-1,1-diphosphonic acid 1.0% 1.0% 1.0% Amino-tris (methylenephosphonic acid) Ethylenediamine tetra (methylenephosphonic acid) 1.0% 0.7% Diethylenetriamine penta (methylenephosphonic acid) 1,5% 1.0% 1.0% Hexamethylenediamine tetra (methylenephosphonic acid) Hydroxyethylamino-di (methylenephosphonic acid) 0.5% 0.5% 0.5% 2-phosphonobutane-1,2,4-tricarboxylic acid 0.5% 0.5% Bis (hexamethylenetriaminepenta (methylenephosphonic acid)) 0.2% 0.2% 0.2% sodium permanganate 0.1% 0.1% 0.1% water 11.1% 11.1% 11.1% 7.3% 7.3% 3.2% 3.9% total 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0%

The first, acidic passivation is applied to steel sheets with a zinc-iron alloy surface, which may be pretreated in a known manner, in particular z. B. cleaned or degreased.

Exemplary embodiments of Tables 3 and 4

On the dried first acid passivation, which was applied from an aqueous acidic composition on the steel sheet with iron-zinc alloy surface, a second, alkaline passivation is applied according to the invention. In the present case, the aqueous acidic compositions for producing a second alkaline passivation, which are explained in more detail below, are applied to the first acidic passivation according to embodiments 1 and 2.

This second passivation is applied as an aqueous composition. The aqueous coating composition is alkaline, although a pH of> 9, preferably between pH 10 and pH 12, although by the use of alkalis can be achieved. However, an alkaline pH is usually already established by using silicates, for example alkali metal silicates. For carrying out the embodiments 3 and 4, polysilicates are used. The solids content (solids based on the total amount of the aqueous solution) is 20% for the preferred lithium polysilicates, 40% for sodium and potassium silicate solutions (water glasses) and 20% for colloidal silicates, with colloidal silicates having a solids content of up to 30%. available and suitable. The molecular weight of the lithium polysilicate is between 200 and 300 g / mol and is thus lower than the molecular weight of the water glasses used. Silane is used in each case with 100% solids. Table 3 Second alkaline passivation (Aqueous composition polysilicate and silane) Silane component Experiment No. lithium polysilicate Experiment No. Natronwasserglas Experiment No. colloidal silicate methacryloyloxymethyltriethoxysilane 1 0 14 0 27 0 methacryloyloxymethyltriethoxysilane 2 15.2 15 1.3 28 27.8 3-aminopropylmethyldiethoxysilane 3 4.1 16 41.5 29 17.3 3 aminopropyltriethoxysilane 4 7.5 17 33.2 30 47.5 N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane 5 70.8 18 1.5 31 13.9 3-glycidyloxypropyltrimethoxysilane 6 19.3 19 2.9 32 28.9 vinyltrimethoxysilane 7 5.9 20 70.2 33 55.5 vinyltriethoxysilane 8th 30.1 21 23.2 34 5.2 methyltrimethoxysilane 9 100.0 22 100.0 35 100.0 methyltrimethoxysilane 10 20.3 23 7.9 36 48.7 3-mercaptopropyltrimethoxysilane 11 7.5 24 21.3 37 2.3 CoatOSil MP 200 * 12 27.5 25 3.9 38 45.0 N- [3- (trimethyloxysilyl) propyl] ethylenediamine 13 25.6 26 9.2 39 44.1 CoatOSil MP 200 is an oligomer of gamma-glycidyloxypropyltrimethoxysilane

Table 3 shows compositions for a second alkaline passivation, the two Reference experiments with lithium polysilicate (experiment no. 1) and methyltrimethoxysilane (experiment no. 9) except, each consisting of a silane-modified silicate. The numerical values indicate in each case the amount of silane used in% by weight based on the total composition of the silane and of the silicate. It is supplemented with silicate to 100% by weight. So z. For example, an aqueous alkaline composition for producing a second alkaline passivation of vinyltrimethoxysilane and lithium polysilicate (Run No. 7) of 5.9 weight% silane and 94.1 weight% lithium polysilicate (20% solid content) together. Here, therefore, the aqueous alkaline composition has an amino-functional, silane-modified lithium polysilicate. An alternative second alkaline passivation is prepared from an aqueous alkaline composition comprising vinyltrimethoxysilane and soda water glass (Run No. 20); this aqueous alkaline composition is composed of 70.2% by weight of silane and 29.8% by weight of silicate (solids content 40%). Here, therefore, the aqueous alkaline composition has a vinyl-functional, silane-modified silicate. Used are colloidal silicate, sodium silicate (sodium polysilicate) and lithium polysilicate, the latter being preferred. A fully hydrolyzed product is used so as to allow substantially VOC-free application of the second alkaline passivation.

The steel sheet treated with the first acidic passivation according to Embodiments 1 and 2 is dipped in the aqueous composition or coating liquid of a silane-modified silicate and then dried, using the same conditions as described for producing the first acidic passivation.

Also well suited as a second alkaline passivation are alkaline aqueous compositions which have a silicate modified with various silanes. Table 4 shows those compositions in which up to eight different silanes are used, each for the modification of a silicate.

The experiments in Tables 3, 4 show that for the silane-modified silicate, the proportions of silane and silicate can be varied within a wide range. The silicate content can vary between 1% and 99% by weight; it is preferably between 20% by weight and 90% by weight. The silane can be used in the same amounts become like the silicate; both are each used in complementary proportions, so that they add up to 100% by weight in the formulations given here. Preferably up to 20% by weight of silane are used. Based on the solids content, according to a particularly advantageous embodiment, lithium polysilicate and silane are used in a ratio of about 1: 1.

With the first, acidic passivation, very thin layers of up to 300 nm are applied, usually up to 150 nm, preferably up to 100 nm. Despite the low layer thickness, the first passivation according to the invention produces good corrosion protection. The second alkaline passivation is applied in a layer thickness of up to 1 μm, advantageously from 10 nm to 500 nm. The thickness of the second layer is preferably 300 nm here. Table 4 Second Alkaline Passivation (Aqueous composition polysilicate and several silanes) Silane component / experiment no. 40 41 42 43 44 methacryloyloxymethyltriethoxysilane 1.0% 15.0% 0.0% 5.0% 2.0% 3-aminopropylmethyldiethoxysilane 5.0% 1.0% 3-aminopropyltriethoxysilane 1.3% N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane 15.0% 3-glycidoxypropyltrimethoxysilane 4.0% 20.0% 21.0% 5.0% vinyltrimethoxysilane 5.0% 2.0% 2.7% 5.0% vinyltriethoxysilane 1.5% 3-mercaptopropyltrimethoxysilane 5.0% 3.0% CoatOSil MP 200 * 5.0% 25.0% 2.0% 5.0% 45.0% N- [3- (trimethyloxysilyl) propyl] ethylenediamine 15.0% 6.0% 5.0% 7.5% Silicate component, each used as a polysilicate lithium polysilicate 90.0% Natronwasserglas 70.0% 55.0% colloidal silicate 20.0% 30.0% CoatOSil MP 200 is an oligomer of gamma-glycidyloxypropyltrimethoxysilane

The aqueous composition for the second alkaline passivation was prepared by co-hydrolysis of the silanes or siloxanes and the silicates, in this case polysilicates, and subsequent removal of the liberated alcohols by means of vacuum distillation.

The first acidic passivation compositions (Tables 1, 2) and the second alkaline passivation (Tables 3, 4) described in Tables 1-4 were successively applied to steel sheets as described above in connection with the application of the first, acidic passivation explained.

For comparison, however, untreated steel sheets and steel sheets were tested, which were provided only with a first acid passivation or only with a second passivation. These comparative objects and the steel sheets provided according to the invention with both acidic and alkaline passivations were then subjected to the neutral salt spray test DIN EN ISO 9227. The results of this test are summarized in Table 5. All steel sheets used for carrying out the embodiments 1 to 4 have a zinc alloy surface.

Line 1 of Table 5 shows in each case the corrosion protection results for steel sheets which were tested with first, acidic passivation but without second alkaline passivation. Column 1 of Table 5 shows steel sheets which were tested without first, acidic passivation, but with second, alkaline passivation. The test result in column 1 and line 1 shows the test results for a sheet steel without passivation.

Columns 1-12 of Table 5 respectively show the corrosion protection results for the aqueous compositions of the first, acidic passivation listed in Tables 1 and 2. Lines 1-44 in Table 5 show the second, alkaline passivations applied to these acidic passivations.

The compositions of the first, acidic passivation of Experiments 1, 5 and 7 were carried out without vanadium or tungsten compounds.

• -- kein Korrosionsschutz: Standzeit im Salzsprühtest < 24 Stunden
• - mäßiger Korrosionsschutz: Standzeit im Salzsprühtest >24 Stunden
• O durchschnittlicher Korrosionschutz:
  Standzeit im Salzsprühtest >48 Stunden
• + guter Korrosionsschutz: Standzeit im Salzsprühtest >150 Stunden
• ++ hervorragender Korrosionsschutz:
  Standzeit im Salzsprühtest >360 Stunden (Weissrost),
  Standzeit im Salzsprühtest >720 Stunden (Rotrost)

The results shown in Table 5 were evaluated as follows:

• - no corrosion protection: service life in the salt spray test <24 hours
• - moderate corrosion protection: service life in the salt spray test> 24 hours
• O average corrosion protection:
  Service life in the salt spray test> 48 hours
• + good corrosion protection: service life in the salt spray test> 150 hours
• ++ excellent corrosion protection:
  Life in the salt spray test> 360 hours (white rust),
  Service life in the salt spray test> 720 hours (red rust)

In detail, comparing each of the first column in Table 5 with the other columns, it can be seen that, without initial, acidic passivation, an average corrosion protection can be achieved at best even with an otherwise very effective second, alkaline passivation. On the other hand, it shows that it is important for the construction of a good or outstanding corrosion protection that an acidic passivation has already been applied in advance, but that the quality of the measured corrosion protection for the two-layer passivation according to the invention depends more on the composition of the second, alkaline passivation. This can be seen from the fact that the results in a row (except column "without") are to be classified equally.

Further, it appears that second alkaline passivation compositions containing a silane-modified lithium polysilicate are most effective in providing excellent corrosion protection when applied to an acidic passivation (Run 1-13 second passivation). Particularly good results are provided by acidic and alkaline passivations according to the invention if the acidic passivation contains vanadium, tungsten or compounds thereof. But even the aqueous alkaline compositions of a silicate modified with several silanes cause predominantly excellent corrosion protection on the surface of an acidic passivation.

Alkaline passivation using colloidal silicate or water glass in combination with silane, ie silane-modified, and applied to an acidic passivation leads to good, sometimes excellent, results in neutral Salt spray test.

The steel sheets, which are not or only provided with an acidic or an alkaline passivation, with a surface coated with a zinc-iron alloy and which also contain a zinc-iron alloy according to the invention with a first acidic passivation and a second alkaline passivation. Alloy surface steel sheets were tested for corrosion resistance in the neutral salt spray test as discussed above. A steel sheet having a surface of a zinc-iron alloy but without any coating shows a corrosion resistance of less than 24 hours (experiment column 1, line 1: -). Zinc-iron alloy-coated steel sheets which had at least obtained an acidic passivation (line 1 tests) or which alone had undergone alkaline passivation (column 1 tests) have low to average corrosion resistance in the salt spray test.

Steel sheets with a zinc-iron alloy surface, to which both a first, acidic passivation and a second, alkaline passivation comprising silane-modified silicates has been applied, generally show at least good, but often excellent corrosion protection.

Particularly noteworthy are the results for the acid passivated substrates prepared using vanadium and tungsten compounds (Experiments 2-4, 6, 8-12), which were then treated according to the invention with a second alkaline passivation.

In evaluating the effect that the second alkaline passivation contributes to corrosion protection, it appears that alkaline passivations with lithium polysilicate predominantly (Runs 1-13) provide excellent corrosion protection, particularly when lithium polysilicate is modified with one or more silanes or siloxanes.

Colloidal silicates or silica sols also lead to good corrosion protection resistance, especially when the colloidal silicates are modified in conjunction with silanes or siloxanes (experiments lines 28-39, 41, 44). The same applies to silicates which are simultaneously modified in a mixture with several silanes or siloxanes. Here, predominantly excellent results are achieved in the salt spray test.

But the water glasses are also very well suited for the production of aqueous, alkaline passivation solutions; Passivations prepared with such solutions show, especially when the silicates used have been modified with silanes or siloxanes, good corrosion protection results (Experiments 14-26, 42, 43).

It should be noted that these passivations, which provide good to excellent corrosion protection, can do without cobalt and no chromium VI compounds. It should also be emphasized that these acidic and alkaline passivations can be applied substantially VOC-free and dried, not least because preference is given to using completely hydrolyzed silane-modified silicates, in particular polysilicates.

It can also be seen that the effect of the second alkaline passivation does not depend on the composition of the first, acidic passivation. Rather, it turns out that in the combination of an acidic and an alkaline passivation, a good to very good corrosion protection can be achieved even if z. B. little or no vanadium or tungsten compounds or phosphonic acid are included in the acidic passivation.

Claims (32)

A method for producing a metallic substrate provided with a chromium-VI-free and cobalt-free passivation by applying a first acidic passivation and a second alkaline passivation to the metallic substrate, characterized in that an aqueous alkaline composition is used for producing the second alkaline passivation, having the silane-modified and / or siloxane-modified silicates. A method according to claim 1, characterized in that the second alkaline passivation, an aqueous alkaline composition is applied to the substrate having a silane-modified and / or siloxane-modified silicate in a proportion of 1% to 99% by weight of silane. A method according to claim 1 or 2, characterized in that for the preparation of the second alkaline passivation, an aqueous alkaline composition is applied to the metallic substrate having one or more silicates from the group comprising colloidal silica sols, sodium, potassium, lithium and ammonium silicate, all silicates also present as polysilicates. A method according to claim 3, characterized in that for preparing the second alkaline passivation, an aqueous alkaline composition is applied, the lithium polysilicate or a mixture of lithium polysilicate with colloidal silica sols, sodium, potassium and / or ammonium silicate. Process according to at least one of Claims 1 to 4, characterized in that the aqueous alkaline composition applied for producing the second alkaline passivation comprises a vinyl-, amino- or epoxy-functional silane and / or a siloxane or a mixture of these silanes or siloxanes. A method according to claim 5, characterized in that the aqueous solution applied for the preparation of the second alkaline passivation comprises one or more silanes from the group comprising methacryloxymethyltriethoxysilane, methacryloxymethyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, N- (2-aminoethyl) -3 -aminopropylmethyldimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, vinyltri-methoxysilane, vinyltriethoxysilane, methyltrimethoxysilane, methyltrimethoxysilane and 3-mercaptopropyltrimethoxysilane and siloxanes. Method according to one of claims 1 to 6, characterized in that the aqueous alkaline composition used to prepare the second alkaline passivation silicates, silanes, siloxanes, silane-modified and / or siloxane-modified silicates, which are used in partially or completely hydrolyzed form. Method according to at least one of the preceding claims 1 to 7, characterized in that a substrate is coated, which has a metallic surface, from the group consisting of a surface of zinc, aluminum, a zinc-aluminum alloy, a zinc-iron alloy or an alloy of zinc or aluminum with one or more other metals. Method according to at least one of the preceding claims 1 to 9, characterized in that the second alkaline passivation has a layer thickness of 10 nm to 1 micron, preferably from 20 nm to 500 nm. Method according to at least one of claims 1 to 10, characterized in that a first acidic passivation is applied, which is optionally subsequently dried, and that a second alkaline passivation is applied to the dried, first passivation. Method according to at least one of the preceding claims 1 to 11, characterized in that, for the preparation of the first, acidic passivation, an aqueous acidic composition is applied to the substrate which has a chromium (III) compound selected from the group consisting of Chromium (III) sulfate, chromium (III) hydroxide, chromium (III) dihydrogen phosphate, chromium (III) chloride, chromium (III) nitrate, sodium chromium (III) sulfate, potassium chromium (III) sulfate and chromium (IIB) salts of organic acids. A method according to any one of claims 1 to 11, characterized in that for the preparation of the first, acidic passivation, an aqueous acidic composition is applied to the substrate having a nitrate compound. A method according to any one of claims 1 to 13, characterized in that for the preparation of the first, acidic passivation, an aqueous acidic composition is applied to the substrate having a fluorine source, wherein as the fluorine source, a compound is selected from the group comprising Hydrofluoric acid, hexafluorotitanic acid, hexafluorozirconic acid, sodium fluoride, potassium fluoride, ammonium fluoride, sodium bifluoride, potassium bifluoride and ammonium bifluoride. A method according to any one of claims 1 to 13, characterized in that for the preparation of the first, acidic passivation, an aqueous acidic composition is applied to the substrate having one or more compounds of the metals molybdenum, vanadium or tungsten. A method according to any one of claims 1 to 14, characterized in that for the preparation of the first, acidic passivation, an aqueous acidic composition is applied to the substrate having one or more of the compounds selected from the group consisting of potassium molybdate, sodium molybdate, potassium orthovanadate, potassium metavanadate , Sodium orthovanadate, sodium metavanadate, sodium tungstate, sodium paratungstate and vanadium pentoxide. A method according to any one of claims 1 to 15, characterized in that for the preparation of the first, acidic passivation, an aqueous acidic composition is applied to the substrate comprising a phosphonic acid and / or derivatives thereof. A method according to claim 16, characterized in that for the preparation of the first acidic passivation, an aqueous acidic composition is applied to the substrate, wherein one or more acids are used from the group comprising (1-hydroxyethane-1,1-diyl) Biphosphonic acid, 2-phosphonebutanel 1,2,4-tricarboxylic acid, aminotrimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid or diethylene triamine penta methylene phosphonic acid. A method according to claim 16, characterized in that for the preparation of the first acidic passivation an aqueous acidic composition is applied to the substrate comprising phosphonates individually or in mixture, from the group comprising tetrasodium (1-hydroxyethane-1,1-) di-alkyl) bisphosphonate, tri-sodium (1-hydroxy-ethane-1,1-diyl) biphosphonate, pentasodium ethylenediamine tetramethylene phosphonate or heptasodium diethylene triamine pentamethylene phosphonate. A method according to any one of claims 1 to 18, characterized in that for the preparation of the first acidic passivation, an aqueous acidic composition is applied to the substrate having one or more of the elements or their compounds, from the group comprising molybdenum, manganese , Cerium, lanthanum. Method according to at least one of the preceding claims 1 to 19, characterized in that the first acidic passivation has a layer thickness of 10 nm to 1 μm, preferably up to 500 nm. Aqueous acidic chromium VI-free and cobalt-free composition for passivating a substrate comprising a chromium (III) compound, an acid and a fluorine source, characterized in that the composition comprises one or more compounds of the metals molybdenum, vanadium or tungsten. Aqueous acidic chromium VI-free and cobalt-free composition according to claim 21, characterized in that one or more of the compounds from the group consisting of potassium molybdate, sodium molybdate, potassium orthovanadate, potassium metavanadate, sodium orthovanadate, sodium metavanadate, sodium tungstate are used as the compound of the metals vanadium or tungsten , Sodium paratungstate and vanadium pentoxide. A metallic substrate having a cobalt-free passivation comprising the elements chromium, fluorine and at least one of the elements of the group comprising molybdenum, vanadium and tungsten. Metallic substrate with a cobalt-free passivation according to claim 23, characterized in that the passivation metal-oxygen compounds of the metals molybdenum, vanadium and / or tungsten. A metallic substrate with a cobalt-free passivation according to claim 23, comprising silane-modified and / or siloxane-modified silicate. Metallic substrate according to at least one of claims 23-25, characterized in that a first passivation layer is applied directly to the substrate, in which the elements comprise chromium, fluorine and at least one of the elements of the group, molybdenum, vanadium, tungsten and metallic and rare earth elements , are detectable. Metallic substrate according to claim 26, characterized in that a second passivation layer is applied to the first passivation layer in which silicon and / or sodium, potassium or lithium are detectable. Metallic substrate according to at least one of claims 23-27, characterized in that the second passivation layer comprises silicon-carbon bonds. Metallic substrate according to at least one of claims 23-28, characterized in that the first passivation layer and the second passivation layer each have a layer thickness of 10 nm to 1 μm. Metallic substrate according to at least one of claims 23-29, characterized in that a metallic substrate is provided with a passivation having a surface of zinc, aluminum, steel, iron or of a zinc or an aluminum alloy. Apparatus for applying a multi-stage passivation to a substrate comprising a first application device for applying a first acidic composition for passivation and a second application device for applying a second, alkaline composition for passivation. Apparatus according to claim 31, characterized in that after a device for applying a first acidic or second alkaline composition for passivation, a dryer for removing liquid from the surface of the substrate is provided.