EP2507408A1

EP2507408A1 - Multi-stage pre-treatment method for metal components having zinc and iron surfaces

Info

Publication number: EP2507408A1
Application number: EP10776723A
Authority: EP
Inventors: Jan-Willem Brouwer; Frank-Oliver Pilarek; Jens KRÖMER; William E. Fristad; Helene Maechel
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2009-12-04
Filing date: 2010-11-15
Publication date: 2012-10-10
Anticipated expiration: 2030-11-15
Also published as: US20120325110A1; US8715403B2; ES2642079T3; WO2011067094A1; JP2013513022A; CN102639750A; PL2507408T3; BR112012013126A2; BR112012013126B1; CN102639750B; DE102009047522A1; HUE035823T2; EP2507408B1; JP5837885B2

Abstract

The invention relates to an acidic, aqueous, chromium-free composition (A) for the anti-corrosive treatment of steel and/or galvanized steel surfaces comprising metal ions (M) selected from ions at least of the elements nickel, cobalt, molybdenum, iron or tin and a multi-stage method applying the composition (A) for the anti-corrosive pre-treatment of metal components which have steel and/or galvanized steel surfaces. The invention further relates to metal surfaces of zinc or iron having a passive layer system comprising at least 30 mg/m²nickel and at least 10 mg/m² zircon, titanium and/or hafnium and sulfur, wherein nickel is present in metallic form at up to at least 30 At.-%, obtainable in a method according to the invention.

Description

"Multistage pretreatment process for metallic components with

Zinc and iron surfaces "

The present invention relates to an acidic, aqueous, chromium-free composition (A) for the anticorrosive treatment of steel and / or galvanized steel surfaces, comprising metal ions (M) selected from ions of at least one of the elements nickel, cobalt, molybdenum, iron or tin, and a multi-stage process using the composition (A) for the anticorrosive pretreatment of metallic components having surfaces of steel and / or galvanized steel. Furthermore, the invention relates to metallic surfaces of zinc or iron, which have a passive layer system containing at least 30 mg / m ² nickel and at least 10 mg / m ² zirconium, titanium and / or hafnium and sulfur, wherein nickel is at least 30 at .-% in metallic form, obtainable in a method according to the invention.

Corrosion inhibitors, which are an acidic aqueous solution of fluoro complexes, have long been known and substitute those long used in the art

Chromating process for passivating pretreatment. Recently, such

Corrosion inhibitor, which only a thin conversion layer on the treated

Metal surfaces, also discussed as a replacement for Phosphatierverfahren and

especially in the automotive supply industry used to multi-level

Substituting phosphating, which is associated with high substance conversions, against methods with lower material conversion and lower process complexity. As a rule, such solutions of fluoro-complexes contain further corrosion-protecting

Active substances that further improve the corrosion protection effect and paint adhesion.

For example, WO 07/065645 describes aqueous compositions containing fluorocomplexes of, inter alia, titanium and / or zirconium, wherein in addition a further component is present, which is selected from: nitrate ions, copper ions, silver ions, vanadium or vanadate ions, bismuth ions, magnesium ions, zinc ions, manganese ions, cobalt ions, nickel ions, tin ions, buffer systems for the pH range from 2.5 to 5.5, aromatic carboxylic acids with at least two groups containing donor atoms, or derivatives of such carboxylic acids, silica particles having a mean particle size below 1 μιη.

There is a need to further advance the anticorrosive pretreatment of metal surfaces and to introduce them to the corrosion protection and paint adhesion performance of a trication zinc phosphating. It is no longer the number of individual process steps that is decisive for the success of a pretreatment, but the performance of the coating, in particular with regard to the pretreatment of components composed of the materials steel, galvanized steel and aluminum. From the published patent WO 2009045845 is an electroless metallizing

Pretreatment before a zirconium-based conversion treatment of metal surfaces, in particular of steel and galvanized steel, known. In this case, a pretreatment with an acidic aqueous composition containing water-soluble salts of electropositive metals selected from nickel, copper, silver and / or gold is carried out before the conversion treatment. Such a composition for metallization may additionally contain defoamers and wetting agents. When using sparingly soluble copper salts, it is proposed to use complexing agents in WO 2009045845 in order to increase the concentration of copper ions in the metallizing composition. It turns out that in the WO

2009045845 proposed before a conversion treatment does not reach the paint adhesion and corrosion resistance, which can be achieved by zinc phosphating and subsequent dip coating.

The publication US 5032236 describes the electrolytic layer formation

Steel surfaces to form black coatings using largely

Chromium (VI) -free electrolyte containing at least 50 g / l of zinc ions and at least 50-300 g / l of metal cations selected from cations of the elements iron, cobalt and / or nickel. In addition, the aqueous composition may contain electropositive metal cations of the elements copper, silver, tin and / or bismuth. Further constituents of the electrolytic layer formation compositions disclosed in US Pat. No. 5,032,236 are ionogenic compounds which improve the formation of layers, including inorganic and organic sulfur compounds. According to the teaching of US Pat. No. 5,032,236, such an electrolytic layer formation can be followed by a chromating followed by the deposition of an immersion varnish to build up a corrosion-protecting layer system on steel surfaces, wherein according to this process sequence coated steel surfaces offer a good protection against corrosion with good paint adhesion values. As a disadvantage of this electrolytic process, on the one hand prove the consumption of electrical energy and the other for the process

necessary high concentrations of the ionogenic constituents, the use of

Badstabilisatoren and a complex apparatus bathroom care in terms of regeneration of its active components and the disposal of unavoidable heavy metal sludge require.

From the US 4278477 the expert takes an alkaline aqueous composition containing metal cations selected from ions of the elements cobalt, nickel, iron and / or tin in an amount of 0.01-1 g / l, a complexing agent selected from pyrophosphate and / or Nitrilotriacetic acid for preventing the precipitation of sparingly soluble heavy metal salts and optionally a reducing agent, preferably sulfite. Such alkaline compositions are suitable according to the teaching of US 4278477 for electroless coating of

Zinc surfaces, wherein such a coated zinc surface after chromating and application of a paint system high corrosion resistance at good paint adhesion values having. Due to the low ionic concentrations and the presence of the complexing agent, a high bath stability is ensured. However, that allows in the

US 4,278,477, does not disclose satisfactory pretreatment of steel surfaces and the compositions contain relatively high levels of complexing phosphates and / or nitrilotriacetic acid, which are of environmental concern.

Accordingly, there is no multistage process for anticorrosive pretreatment of both zinc and steel surfaces in the prior art

Corrosion protection and paint adhesion properties of a trication zinc phosphating is at least equivalent and can be operated in a resource-saving manner.

The object of the present invention is therefore to provide a method for

to establish corrosion-protective pretreatment, which is suitable for the subsequent application of organic coating systems, does not comprise electrolytic process steps and in which the deposition of small amounts of active components is sufficient for effective corrosion protection, without significant amounts of these active components through

Settle precipitation reactions due to the process in the treatment and must be worked up if necessary. In addition, in a method according to the invention, it should be possible, as it were, to provide different metal surfaces of a component, which are surfaces of steel, galvanized steel and aluminum, with an anticorrosive coating at least equivalent to a trication zinc phosphating.

This problem is solved by a multi-stage process for corrosion protection

Pretreatment of metallic components having surfaces of steel and / or galvanized steel, comprising the method steps i-iii), each of which involve contacting the metallic component with an aqueous treatment solution, wherein the respective method steps i-iii) follows are characterized:

i) cleaning and degreasing the metal surface;

ii) electroless treatment by contacting the metal surface with a

acidic aqueous, chromium-free composition (A) according to the present invention;

iii) containing passivating treatment by contacting the metal surface with an acidic aqueous composition (B)

a) at least one water-soluble compound of the elements Zr, Ti and / or Hf in one

Concentration of at least 5 ppm based on the elements Zr and / or Ti, the process steps ii) and iii) are carried out with or without intermediate rinsing step always after cleaning and degreasing of the metal surface, but in any order.

An acidic aqueous, chromium-free composition (A) according to the invention which, when brought into contact with steel and / or galvanized steel, in a process according to the invention effective corrosion protection already effected by deposition of small amounts of active components contains

a) at least 100 ppm of metal ions (M) selected from ions of at least one of

Elements nickel, cobalt, molybdenum, iron or tin,

b) at least one water-soluble compound containing sulfur in an oxidation state

less than +6,

c) less than 10 g / l of zinc ions,

d) a total of less than 1 g / l of dissolved phosphates calculated as P0 ₄ ,

and preferably has a pH in the range of 3.0 to 6.5.

If, in the process according to the invention, metallic components comprising steel and galvanized steel are treated with a composition (A) according to the invention, the surface of the metallic component consisting of at least 10% galvanized steel surfaces, the pH is preferably in the range from 4.0 to 7.0, more preferably in a range of 5.0 to 7.0, especially in the range of 6.0 to 6.8.

According to the invention, the composition (A) is chromium-free, if less than 10 ppm,

preferably less than 1 ppm of chromium, in particular no chromium (VI) are contained.

By the electroless treatment of the metal surfaces after the degreasing stage and before or after the passivating treatment of the method according to the invention with a

Composition (A) causes deposition of the metal ions (M) (active component) on the metal surfaces. The layer formation takes place at least partially in the form of metallic phases of the elements nickel, cobalt, molybdenum, iron or tin.

The layer-forming deposition of the metal ions (M) in the presence of the reducing water-soluble compound containing sulfur in an oxidation state less than +6 is inhibited in the presence of zinc ions. The composition (A) according to the invention therefore contains less than 10 g / l.

In a preferred embodiment, the composition (A) may additionally contain chelating organic compounds which have at least two functional groups with oxygen and / or nitrogen atoms selected from carboxyl, hydroxyl, amine, phosphoric acid or phosphonic acid groups. Particularly preferred are chelating organic compounds containing phosphoric acid, phosphonic acid and / or hydroxyl groups, for example, 1-hydroxyethane (1, 1 -diphosphonic acid). It has been found that such chelating agents in the composition (A) according to the invention mainly complex zinc ions and therefore weaken the inhibition of the deposition of the metal ions (M) on the metal surfaces. The chelating organic compounds are preferably contained in such an amount that the molar excess of zinc ions relative to the chelating organic Compounds not greater than 2 g / l, preferably not greater than 1 g / l, more preferably not greater than 0.5 g / l of zinc ions.

Overall, however, those compositions (A) are preferred whose content of zinc ions is not greater than 2 g / l, preferably not greater than 1 g / l, more preferably not greater than 0.5 g / l of zinc ions.

The amount of phosphate ions is limited in the compositions (A) according to the invention, since higher proportions can cause the formation of a thin phosphate passivation, which is disadvantageous for the deposition of the metal ions (M) on the metal surfaces. This is surprising as the passivating treatment of the metal surface with a

Composition based on zirconium, titanium and / or hafnium, analogously to the treatment step iii) according to the invention, is not detrimental to the layer-forming deposition of the metal ions (M). Therefore, such compositions (A) according to the invention are preferred in which the proportion of dissolved phosphate is not more than 500 ppm, more preferably not more than

200 ppm, more preferably not more than 50 ppm calculated as P0 ₄ .

The presence of water-soluble compounds of the elements zirconium, titanium and / or hafnium in a composition (A) according to the invention can inhibit the deposition of the metal ions (M) on the steel surfaces. In addition, such compositions (A) do not result in precipitation of zirconium, titanium and / or hafnium so that the use of these compounds provides no advantage and is uneconomical. According to the invention, preference is given to compositions (A) according to the invention whose content of zirconium, titanium and / or hafnium in the form of water-soluble compounds is in total less than 20 ppm, more preferably less than 5 ppm.

The at least one water-soluble compound containing sulfur in an oxidation state of less than +6 is preferably selected from inorganic compounds, more preferably from oxo acids of sulfur such as sulphurous acid, thiosulphuric acid, dithionic acid, polythionic acid, sulphurous acid, dibasic acid and / or dithionic acid and their salts, especially preferably from sulphurous acid. The water-soluble compound containing sulfur may also be selected from salts of the organic acids thiocyanic acid and / or thiourea, with the aforementioned water-soluble inorganic compounds containing sulfur being preferred over organic acids and salts.

The oxidation state, in the context of the present invention, is defined according to IUPL Rule I-5.5.2.1 ("Nomenclature of Inorganic Chemistry - Recommendations 1990", Blackwell: Oxford, 1990) and designates the hypothetical charge assigned to an element in a molecule would be if this element were to be assigned all the electrons shared with other elements of the molecule for which the element has a higher electronegativity than that of the element with which it shares the electrons. The preferred concentration of water-soluble compounds containing sulfur in an oxidation state less than +6 is at least 1 mM, preferably at least 5 mM, but not more than 100 mM, preferably not more than 50 mM. Below 1 mM is one

Layer-forming deposition of metal ions (M) in typical treatment times of a few minutes is not given or does not occur. Above 100 mM, on the one hand, no further acceleration of the layer formation on contacting a cleaned steel surface with such a composition (A) is found, and on the other hand, higher amounts of sulfur-containing compounds are rejected for economic and occupational hygiene reasons.

Other reducing agents based on water-soluble compounds containing phosphorus and / or nitrogen in an oxidation state of less than +5 are surprisingly unsuitable for the deposition of the metal ions (M), in particular for the deposition of nickel and / or cobalt ions that these reducing agents in the composition (A) for economic reasons, preferably not or only in very small amounts below 50 ppm are included.

In inventive compositions (A) are preferably at least 0.2 g / l, but not more than 5 g / l, preferably not more than 2 g / l of metal ions (M) selected from ions of at least one of the elements nickel, cobalt , Molybdenum, iron or tin. If this value is undershot, the activity of the metal ions (M) in the composition (A) is usually too low for adequate deposition. Above 5 g / l there is no additional benefit, whereas the increased precipitation of insoluble salts of the metal ions (M) increases, so that such high concentrations of metal ions (M) in treatment baths according to step ii) of the process according to the invention are uneconomical and also require increased processing costs.

As metal ions (M) which are deposited on the metal surfaces in process step ii) from the acidic aqueous composition (A), in a preferred embodiment, in particular nickel and / or cobalt, more preferably nickel.

Metal surfaces of steel and / or galvanized steel, which are brought into contact with an aqueous composition (A) containing nickel and / or cobalt ions, particularly preferably nickel ions, independently of the sequence of process steps ii) and iii) are provided within a short treatment time with a thin layer containing the elements nickel and / or Kolbalt, which gives an excellent paint adhesion to subsequently applied organic paint systems and thereby meets the highest standards of corrosion protection.

Preferred water-soluble compounds which release metal ions (M) are all water-soluble salts which do not contain chloride ions. Particular preference is given to sulfates, nitrates and acetates. A preferred composition (A) according to the invention has a molar ratio of metal ions (M) selected from ions of at least one of nickel, cobalt, molybdenum, iron or tin to water-soluble compounds containing sulfur of not greater than 1: 1, preferably not greater than 2: 3 but not less than 1: 5. Above this preferred molar ratio of 1: 1, the formation of the thin layer containing the elements of the metal ions (M) is slower, so that in particular for the application of

Composition (A) in process step ii) of an inventive

A coating process is preferably those compositions (A) in which a sufficient amount of water-soluble compounds containing sulfur relative to the total amount of metal ions (M) is present. Conversely, a molar ratio of metal ions (M) to water-soluble compounds containing sulfur below 1: 5 may be detrimental to the stability of compositions (A) of the invention because the reducing sulfur compounds can then cause precipitation of the containing metals in colloidal form.

For compositions (A) according to the invention, it may be advantageous to add electropositive metal cations in order to accelerate the layer formation. A preferred

Embodiment of the invention therefore additionally contains copper ions and / or silver ions, preferably copper ions, in an amount of at least 1 ppm, but not more than 100 ppm. Above 100 ppm, the deposition of the electropositive metal in elemental form on the steel and / or galvanized steel surfaces dominate so far that the layer formation based on the metal ions (M) is pushed back so far that the paint adhesion applied subsequently in the process according to the invention organic paints is significantly deteriorated or inhomogeneous layer coatings are produced after step ii) of the method according to the invention, which offer a poorer corrosion protection.

Preferred water-soluble compounds that release copper ions are all

water-soluble copper salts containing no chloride ions and all water-soluble silver salts. Particular preference is given to sulfates, nitrates and acetates.

Likewise, the addition of water-soluble compounds, which are a source of fluoride ions, to a composition (A) according to the invention may be preferred, wherein the

Concentration of total fluoride in the composition (A) is preferably at least 50 ppm but not more than 2000 ppm. The addition of fluoride is particularly advantageous when, in a process according to the invention, step ii), with or without a rinsing step between them, immediately follows the purification step i) and in particular when hot-dip galvanized steel surfaces are treated. In such a case, the pickling rate on the metal surfaces and faster deposition kinetics of the thin increases

Coating consisting of elements of metal ions (M) and a more homogeneous

Coating the metal surface is the immediate consequence. Below a total fluoride amount of 50 ppm, this additional positive effect is hardly pronounced, while above 2000 ppm no further increase in the deposition kinetics, but the precipitation of insoluble fluorides is disadvantageous. Preferred water-soluble compounds which serve as a source of fluoride ions are hydrogen fluoride, alkali fluorides, ammonium fluoride and / or

Ammonium.

In methods according to the invention comprising the individual steps i-iii), a cleaning and degreasing of the metal surface is necessary for a homogeneous formation of the passivating coating according to process steps ii) and iii). In particular, those purification steps i) are preferred according to the invention, which are carried out by means of an aqueous cleaning solution, wherein the cleaning a Beizabtrag of at least 0.4 g / m ² , but not more than 0.8 g / m ^{2 of} zinc based on a surface of Electrolytic galvanized steel causes. The person skilled in the art knows cleaners which have a corresponding pickling rate for a given cleaning time. It has surprisingly been found that such a preferred purification leads to better results in terms of corrosion protection and paint adhesion of the steel and / or galvanized steel surfaces treated according to the invention.

The acidic aqueous used in step iii) of the process according to the invention

Compositions (B) are preferably free of chromium, i. they contain less than 10 ppm, preferably less than 1 ppm of chromium, in particular no chromium (VI). Furthermore, the acidic compositions (B) in the process according to the invention preferably contain a total of 20 to 1000 ppm of water-soluble compounds of the elements zirconium, titanium and / or hafnium based on the elements zirconium, titanium and / or hafnium. If less than 20 ppm of the elements zirconium, titanium and / or hafnium contain an insufficient conversion of the purified or treated in step ii) metal surface may be the result so that only small amounts of hydroxides and / or oxides of these elements deposited and the passivating effect is too low. Above 1000 ppm, based on the elements zirconium, titanium and / or hafnium in the composition (B), however, a further improvement in the corrosion properties of the metal surfaces treated according to the invention can not be determined.

Preference is furthermore given to those acidic aqueous compositions (B) in the process according to the invention which contain, as water-soluble compounds of the elements zirconium, titanium and / or hafnium, only water-soluble compounds of the elements zirconium and / or titanium, more preferably water-soluble compounds of the element zirconium.

Preferred water-soluble compounds of the elements zirconium, titanium and / or hafnium are compounds which dissociate in aqueous solution into anions of fluorocomplexes of the elements zirconium, titanium and / or hafnium. Such preferred compounds are, for example, H ₂ ZrF ₆ , K ₂ ZrF ₆ , Na ₂ ZrF ₆ and (NH ₄ ) ₂ ZrF ₆ and the analogous titanium compounds. Also, fluorine-free compounds of the elements zirconium, titanium and / or hafnium can be used as water-soluble

Compounds are used according to the invention, for example (NH ₄ ) ₂ Zr (OH) ₂ (C0 ₃ ) ₂ or TiO (S0 ₄ ). In addition, a composition (B) in step iii) of the process according to the invention may contain 1 to 100 ppm of copper ions and optionally up to 200 ppm of free fluoride. The addition of copper ions accelerates the conversion of the purified or treated in step ii) metal surfaces and also increases the passivating effect. Especially in the event that first the passivating treatment of steel and / or galvanized

Steel surfaces, a significant improvement of the film formation in the subsequent step ii) can be found and thus improved corrosion protection properties. Preferred water-soluble compounds that release copper ions are all water-soluble copper salts that do not contain chloride ions. Particular preference is given to sulfates, nitrates and acetates.

The optional addition of fluoride ions in the preferred amount range based on free fluoride, which in turn can be determined by means of an ion-sensitive measuring electrode, facilitates the homogeneous conversion of the purified or treated in step ii)

Metal surfaces. Preferred water-soluble compounds which serve as a source of fluoride ions are hydrogen fluoride, alkali fluorides, ammonium fluoride and / or ammonium bifluoride.

The treatment temperature and the duration of the respective treatment are different in the individual steps i-iii) of the process according to the invention and strongly dependent on the bath system and the type of application, but can be varied over a wide range, without sacrificing corrosion properties.

Preferably, the treatment in steps i-iii) should be carried out as follows:

Process step i): 2-10 minutes at 30-70 ° C

Process step ii): 10-300 seconds at 20-50 ° C

Process step iii): 0.5-10 minutes at 20-50 ° C

The concrete conditions for bringing the metal surfaces into contact with the aqueous treatment stages ii) and iii) are preferably to be selected such that in step ii) a layer coverage of at least 30 mg / ² , more preferably at least 50 mg / ^{m2 of} one or more of the metal ions (M) on the surfaces of zinc, while the temperature and duration of treatment in step iii) are to be adjusted such that a coating of at least 10 mg / m ² zirconium and / or titanium, more preferably at least 25 mg / m ² zirconium and / or titanium on the surfaces of zinc results. Below these preferred layer coverings, the corrosion protection properties of the pretreatment are usually insufficient.

The individual steps i-iii) of the process according to the invention can be carried out with or without an intermediate rinsing step. However, it is preferred that after the purification step i) at least one additional rinsing step with city water or deionized water (κ <1 μ8ϋΐη ^" ) takes place. Surprisingly, exceptionally good results with regard to corrosion protection properties and paint adhesion can be achieved independently of the sequence of steps ii) and iii) in the process according to the invention. In a preferred embodiment, however, the electroless treatment according to method step ii) takes place directly, ie with or without an intermediate rinsing step, after the purification step i). For these preferred

In a first step, the layer formation based on the elements of the metal ions (M) is carried out and then a conversion of the metal surface treated in this way is carried out with the aid of the zirconium- and / or titanium-containing composition (B).

The method according to the invention is suitable for metallic components which have iron, steel and / or galvanized steel surfaces and the corresponding pre-phosphated surfaces. Irrespective of the sequence of steps ii) and iii), sufficient layer formation on the basis of the elements of the metal ions (M) always takes place on these surfaces, which in turn is a prerequisite for the outstanding properties with respect to corrosion and paint adhesion. Likewise, surfaces of aluminum are passivated in step iii) in the process according to the invention, so that the process is particularly suitable for the corrosion-protective pretreatment of multi-metal construction surfaces, for example.

The aqueous compositions in steps i-iii) can be brought into contact with the metal surfaces in both immersion and spraying processes. The method can also be used in the pretreatment of metal strip and there, for example, by means of the roller application method known to those skilled in the art.

The process of the invention is usually followed by the application of a coating system, so that after passing through the process steps i-iii) with or without intermediate rinsing and / or drying step preferably a dip coating or a

Powder coating, particularly preferably a dip coating, in particular a cathodic dip coating follows.

The present invention further comprises a metal surface of iron and / or steel with passive layer system comprising at least 30 mg / m ² nickel and at least 10 mg / m ² zirconium, titanium and / or hafnium, preferably at least 10 mg / m ² zirconium, and sulfur wherein nickel is at least 30 at.% in metallic form, obtainable in a preferred one

process according to the invention, in which step i) with or without intermediate rinsing step directly followed by the electroless treatment according to step ii), the composition (A) in process step ii) at least 100 ppm, but not more than 5 g / l Nickel ions and at least 1 mM sulfurous acid and / or salt thereof and the iron and / or steel surface at a treatment temperature in the range of 20 to 50 ° C is brought into contact with such a composition (A) for at least one minute.

Furthermore, the present invention comprises a metal surface of zinc and / or galvanized steel with a passive layer system comprising at least 30 mg / m ² nickel and at least 10 mg / m ² zirconium, titanium and / or hafnium, preferably at least 10 mg / m ² zirconium, and Contains sulfur, wherein nickel is at least 30 at .-% in metallic form, obtainable in a process according to the invention, in which the process step ii) with or without intermediate rinsing step immediately following the process step iii) and in which the inventive

Composition (A) in process step ii) comprises at least 100 ppm, but not more than 5 g / l of nickel ions and at least 1 mM sulphurous acid and / or salt thereof and the zinc and / or galvanized steel surface at a treatment temperature in the range of 20 to 50 ° C is brought into contact with such a composition (A) for at least one minute.

The invention additionally relates to the use of the metallic components treated according to the invention or of the metal strip treated according to the invention in the manufacture of

Automobile bodies.

EXAMPLES

In the following, the anticorrosion effect of the pretreatment according to the invention for different materials is illustrated by means of a preferred composition (A) according to the invention.

The preferred composition (A) according to the invention has a pH of 3.7 and following

Composition (Examples B1 and B2):

3.1 g / l nickel nitrate solution; 3.8 g / l sodium bisulfite

The preferred process according to the invention (B1 and B2) according to which metal sheets of steel (CRS), hot dip galvanized steel (HDG) and electrolytically galvanized steel (ZE) are treated is characterized by the following individual steps i-iii): i) cleaning and degreasing 55 ° C for 5 minutes with an alkaline cleaner of

Composition:

B1: 3.0% by weight of Ridoline® 1565 A; 0.4% by weight of Ridosol® 1270 (Henkel)

B2: 3.0% by weight Ridoline® 1574 A; 0.4% by weight of Ridosol® 1270 (Henkel)

The approach of the cleaning solution is always with tap water.

A cleaning and degreasing with a cleaning solution as in Example B2 causes a pickling of 0.5 g / m ² on electrolytically galvanized substrates, while a

Cleaning solution according to Example B1 Zinc surfaces not stained. ii) electroless treatment with the above-mentioned preferred composition (A) at 30 ° C for one minute iii) passivating treatment with a zirconium-based pretreatment solution adjusted to a pH of 4.0 and 150 ppm zirconium, 20 ppm Cu and a free fluoride content of 60 ppm, at 30 ° C for two minutes

(TecTalis® 1800, 0.25 g / l Grano Toner® 38, Henkel)

After each of the individual steps i-iii) is followed by a rinsing step with deionized water (κ <1 μ8ϋΐη ^" ).

For comparison purposes, corresponding metal sheets after cleaning and degreasing were determined analogously to step i) above with a conventional trication-phosphating (Granodine® 952, Fa. Henkel, coating weight to 2.0 HDG / EC CRS: 2.5 g / m ² by differential weighing after the removal of the phosphate layer in aqueous 0.5 wt .-% Cr0 ₃ at 20 ° C for 15 min) provided (Comparative Examples V1 and V2) or with a zirconium-based Conversion treatment analogous to the above-mentioned step iii) passivated (Comparative Examples V3 and V4).

The metal sheets treated according to the invention and the comparative sheets were dried with compressed air after the last rinsing step and electrocoated with the following cathodic dip coating: Aqua® 3000 (Dupont Co., KTL layer thickness: 20 μm, determined nondestructively using a commercially available layer thickness gauge)

and then the paint baked at 175 ° C for 25 min in the oven.

Subsequently, the metal sheets were subjected to an alternating climate corrosion test according to VDA 621.415 (10 rounds) or a stone impact test according to DIN EN ISO 20567-1. The resulting test results are summarized in Table 1.

Overall, it can be seen from Table 1 that the metal sheets (B1 and B2) treated according to the invention, which have undergone only a zirconium-based conversion treatment (V3 and V4), both with respect to corrosive infiltration of the paint (U / 2 values) and in the

Stone impact test (K values) is clearly superior.

In addition, the corrosion results show that one of the trication-Zinkphosphatierung (V1 and V2) at least equivalent corrosion-protective coating is realized with the inventive method.

Overall, especially on galvanized surfaces which are treated in a method according to the invention (B1 and B2), a marked improvement in the

Corrosion properties and an increase in the paint adhesion to the KTL reached that are significantly improved even compared to the trication zinc phosphating.

Surprisingly, it appears that the cleaning of the zinc surfaces with a pickling

Cleaning solution a further significantly improved performance of the present invention treated and coated with the dip coating zinc surfaces (B2 vs. B1) causes in the stone impact test. Such an improvement on zinc surfaces by the cleaning effect of the cleaner occurs only in the process according to the invention and is omitted both in the exclusive zirconium-based conversion treatment (V4 vs. V3) and the exclusive trication zinc phosphating (V2 vs. V1). Table 1

Immigrant values and rockfall test

The intolerance of the process according to the invention compared to an excessive amount of zinc and / or phosphate ions is illustrated in Tables 2 and 3.

It turns out that the inhibition of the deposition of nickel in process step ii) by zinc ions is largely independent of the substrate, wherein the inventive method still provides sufficiently good corrosion protection values when the layer support based on the element nickel is at least 30 mg / m ² ,

Tab. 2

Nickel layer coating in mg / m ² as a function of the concentration of zinc ions in a method according to the invention analogously to Example B1 at a varying pH

The nickel layer coating was determined by means of X-ray fluorescence analysis after the individual step iii)

At higher pH values, a larger amount of nickel tends to be deposited on the zinc and steel sheets in the process according to the invention analogously to Example B1, so that the tolerance to zinc ions can be increased in this way. In contrast, the inhibition of nickel deposition in process step ii) by phosphate ions is significantly more pronounced on zinc surfaces than on steel (Table 3). While at a pH of the composition (A) of 3.7 in process step ii) on the steel sheets at a phosphate content of 0.25 g / l still 65 mg / m ² Ni are deposited, which is a sufficient amount for good corrosion protection is, is deposited on zinc sheets under identical conditions no nickel at all. An increase in the bath temperature in process step ii) to 40 ° C in turn causes an increased deposition of nickel, so that on zinc sheets, a coating layer of 92 mg / m ² nickel is measured.

Figure 1 shows an XPS sputter profile (XPS = X-ray photoelectron spectroscopy) of a coating on steel sheet (CRS), which was treated according to Example B1. From this depth profile it can be seen that the treatment of steel in the process according to the invention produces coatings containing not only nickel but also sulfur, and that the conversion treatment in step iii) produces a surface zirconium oxide layer on the nickel-containing coating.

Claims

claims

1. Acid aqueous, chromium-free composition (A) for the electroless treatment of steel and / or galvanized steel surfaces containing

a) at least 100 ppm of metal ions (M) selected from ions of at least one of the elements nickel, cobalt, molybdenum, iron or tin,

b) at least one water-soluble compound containing sulfur in one

Oxidation state less than +6,

c) less than 10 g / l of zinc ions,

d) a total of less than 1 g / l of dissolved phosphates calculated as P0 ₄ .

2. Composition according to claim 1 having a pH in the range of 3.0 to 6.5.

3. Composition according to claim 1 for the electroless treatment of metallic components comprising steel and galvanized steel, wherein the metallic component consists of at least 10% of galvanized steel surfaces, having a pH in the range of 4.0 to 7.0, preferably in the Range of 5.0 to 7.0, more preferably in the range of 6.0 to 6.8.

4. Composition according to one or more of the preceding claims, characterized

characterized in that at least 0.2 g / l, but not more than 5 g / l, preferably not more than 2 g / l of metal ions selected from ions of at least one of the elements nickel, cobalt, molybdenum, iron or tin are.

5. Composition according to one or more of the preceding claims, characterized

in that the molar ratio of metal ions (M) selected from ions is at least one of the elements nickel, cobalt, molybdenum, iron or tin

water-soluble compounds containing sulfur in the composition (A) not greater than 1: 1, preferably not greater than 2: 3, but not less than 1: 5.

6. Composition according to one or more of the preceding claims, characterized

in that the water-soluble compound containing sulfur is selected from water-soluble inorganic compounds, preferably oxo acids of sulfur and their salts, more preferably sulphurous acid and / or salts thereof, and / or from salts of thiocyanic acid and / or thiourea.

7. Composition according to one or more of the preceding claims, characterized

in that additionally copper ions and / or silver ions, preferably copper ions, are contained in an amount of at least 1 ppm, but not more than 100 ppm.

8. Composition according to one or more of the preceding claims, characterized in that additionally water-soluble compounds are present, which are a source of fluoride ions, wherein the concentration of total fluoride in the composition (A) is preferably at least 50 ppm, but not greater than 2000 ppm.

9. Composition according to one or more of the preceding claims, characterized

in that additionally chelating organic compounds containing at least two functional groups with oxygen and / or nitrogen atoms selected from carboxyl, hydroxyl, amine, phosphoric acid or phosphonic acid groups are included.

10. The composition according to claim 9, characterized in that the chelating organic compounds are contained in such an amount that the molar

Excess of zinc ions based on the chelating organic compounds not greater than 2 g / l, preferably not greater than 1 g / l, more preferably not greater than 0.5 g / l of zinc ions.

1 1. Multistage process for the corrosion protection pretreatment of metallic

Components comprising surfaces of steel and / or galvanized steel, comprising the process steps i-iii), each comprising contacting the metallic component with an aqueous treatment solution, wherein the successive

Process steps i-iii) are characterized in each case with or without intermediate rinsing step as follows:

i) cleaning and degreasing the metal surface;

ii) electroless treatment by contacting the metal surface with an acidic aqueous chromium-free composition (A) according to one or more of the preceding claims;

a) at least one water-soluble compound of the elements Zr, Ti and / or Hf in a concentration of at least 5 ppm based on the elements Zr and / or Ti.

12. The method according to claim 1 1, characterized in that the cleaning and degreasing of the metal surface in step i) is carried out by means of an aqueous cleaning solution, wherein in step i) a pickling of at least 0.4 g / m ² zinc based on a surface made of electrolytically galvanized steel.

13. The method according to one or both of the preceding claims 1 1 and 12, characterized

in that the acidic aqueous composition (B) has a total of 20 to

1000 ppm of water-soluble compounds of the elements zirconium and / or titanium to the elements zirconium and / or titanium and optionally 1 to 100 ppm of copper (II) ions and optionally contains up to 200 ppm of free fluoride.

Metal surface of iron with passive layer system containing at least 30 mg / m ² Ni and at least 10 mg / m ² zirconium, titanium and / or hafnium and sulfur, wherein nickel is at least 30 at .-% in metallic form, obtainable in a process according to one or more of claims 1 1 to 13, wherein the purified iron surface in process step ii) with a composition (A) containing at least 100 ppm, but not more than 5 g / l of nickel ions and at least 1 mM sulfurous acid and / or its salt at a treatment temperature in the range of 20 to 50 ° C and a

Treatment time of at least one minute is brought into contact.