EP2292808B1 - Metallising pre-treatment of zinc surfaces - Google Patents

Description

The present invention relates to a process for the metallizing pretreatment of galvanized and / or alloy-galvanized steel surfaces or assembled metallic components, which at least partially comprise surfaces of zinc, in a surface treatment comprising a plurality of process steps. In the process according to the invention, metallic layer deposits of not more than 50 mg / m ² of tin are produced on the treated zinc surfaces. Such metallized zinc surfaces are outstandingly suitable as starting material for subsequent passivation and coating steps ( illustration 1 , Process II-V) and cause a significantly higher efficiency of the anti-corrosion coating, in particular after the pretreatment of galvanized metal surfaces according to the invention. The application of the process on galvanized steel strip prevents corrosive paint infiltration, especially at the cutting edges. In a further aspect, the invention therefore comprises an uncoated or subsequently coated metallic component which has been given a metallizing pretreatment according to the invention, as well as the use of such a component in vehicle body construction in automobile manufacturing, shipbuilding, construction and for the production of white goods.

At present, a large number of surface-refined steel materials are produced in the steel industry, and nearly 80% of the thin-plate products in Germany are today supplied in a surface-refined design. For the production of products, these thin sheet products are further processed, so that a wide variety of metallic materials or various combinations of metallic base and surface material can be present in a component and must be present for certain product requirements, in the further processing, especially of surface-coated strip steel, the material is cut, formed and joined together by means of welding or gluing process. These processing processes are highly typical of the body shop in the automotive industry. There is mainly galvanized steel strip the coil coating industry further processed and assembled, for example, with non-galvanized steel strip and / or strip aluminum. Thus, car bodies consist of a large number of sheet-metal parts which are joined together by spot welding.
From this combination of variety of metallic strip materials in a component and the primary use of surface-treated strip steel, there are special requirements for corrosion protection, which must be able to mitigate both the consequences of bimetallic corrosion and cut edge corrosion. Although metallic zinc coatings, which are applied to the steel strip by electrolytic or hot-dip processes, provide a cathodic protection which prevents active dissolution of the more noble core material at cut edges and mechanically induced damage to the zinc coating, ligation is equally important for ensuring the material properties of the core material the corrosion rate itself. Correspondingly high are the requirements for the corrosion protection coating consisting mostly of an inorganic conversion layer and an organic barrier layer.

At cutting edges and at the zinc coating caused by the machining or other influences, the galvanic coupling between core material and metallic coating brings about an active, unimpeded local dissolution of the coating material, which in turn constitutes an activation point for the corrosive infiltration of the organic barrier layer. The phenomenon of paint peeling or "blistering" is especially observed at the cut edges where unimpeded corrosion of the less noble coating material takes place. The same applies in principle to the locations of a component to which different metallic materials are directly connected by joining techniques. The local activation of such a "defect" (cut edge, damage in the metallic coating, spot welding point) and thus the corrosive paint release resulting from these "defects" is all the more pronounced the greater the electrical potential difference between the metals in direct contact. Correspondingly, good results with regard to paint adhesion at cut edges are offered by steel strips with zinc coatings alloyed with nobler metals, eg iron-alloyed zinc coatings (galvannealed steel).
As the steel strip producers increasingly turn to this, in addition to surface finishing with metallic coatings, further corrosion coatings, in particular Lacquer coatings to integrate into the belt line, there and in the processing industry, particularly in automotive manufacturing, have an increased need for anti-corrosive treatments that effectively prevent the problems associated with cut edge and contact corrosion problems in paint adhesion.

The prior art describes various pretreatments that address the problem of edge protection. An essential strategy is to improve the paint adhesion of the organic barrier layer on the surface-treated steel strip.
The closest prior art is the German Offenlegungsschrift DE19733972 which deals with a process for the alkaline passivating pretreatment of galvanized and alloy-galvanized steel surfaces in strip lines. Here, the surface-treated steel strip is brought into contact with an alkaline treatment agent containing magnesium ions, iron (III) ions and a complexing agent. At the given pH of above 9.5, the zinc surface is passivated thereby forming the corrosion protection layer. Such a passivated surface offers according to the teaching of DE19733972 already a paint adhesion, which is comparable to nickel and cobalt-containing processes. Optionally, this pretreatment can be followed by further treatment steps such as chromium-free post-passivation to improve the corrosion protection before the paint system is applied. Nevertheless, it appears that this pretreatment system can not satisfactorily suppress the paint peeling caused by the corrosion at the cut edges.

It is therefore an object of the present invention to provide a method for the pretreatment of galvanized and alloy-galvanized steel surfaces, which significantly improves the Lackenthaftung emanating from defects in the zinc coating of the steel strip, especially at the cut edges, compared to the prior art.

The publications JP 57188663 A and JP 4048095 A each disclose methods for metallizing pretreatment of galvanized and alloy-galvanized steel surfaces by contacting with aqueous solutions containing tin ions. The aqueous solution of JP 57188663 A is very angry and long contact times of at least 5 minutes are required for satisfactory results. The doctrine of JP 4048095 A In the following, relatively high layer plots of tin of 0.1-0.5 g / m ^{2 are} required in order to correspond to the property profile desired there, in particular with regard to the lubricating effect.

The above object is achieved in this case by a method for metallizing pretreatment of galvanized or alloy-galvanized steel surfaces, wherein the galvanized or alloy-galvanized steel surface is contacted with an aqueous agent (1) for at least 1 second, but not longer than 30 seconds, whose pH Value is not less than 4 and not greater than 8, wherein cations and / or compounds of a metal (A) in the middle (1) are included whose redox potential E _redox measured on a metal electrode of the metal (A) at a given process temperature and concentration cations and / or compounds of the metal (A) in the aqueous medium (1) are more anodic than the electrode potential E _{Zn of} the galvanized or alloy-galvanized steel surface in contact with an aqueous agent (2) which differs from the agent (1) only in that that it contains no cations and / or compounds of the metal (A), characterized gekennzeic hnet that the cations and / or compounds of the metal (A) in the middle (1) are selected from cations and / or compounds of tin in the oxidation states + II and / or + IV and after contacting the galvanized or alloy-galvanized steel surface with the aqueous agent, a metallic coating with metal (A) in a layer of at least 1 mg / m ² , but not more than 50 mg / m ² is present.

The method according to the invention is suitable for all metal surfaces, for example strip steel, and / or assembled metallic components, which at least partially also consist of zinc surfaces, for example automobile bodies. The material combination of iron-containing surfaces and zinc surfaces is preferred.

• mit Ag / AgCl/1M KCl = 0,2368 V gegenüber Standardwasserstoffelektrode (SHE)
• mit M(1) das erfindungsgemäße Mittel (1) enthaltend Kationen und/oder Verbindungen des Metalls (A) bezeichnend

For the purposes of this invention, pretreatment refers to the passivation by means of inorganic barrier layers (eg phosphating, chromating) or a process step preceding the lacquer coating for conditioning the cleaned metallic surface. Such conditioning of the surface causes corrosion protection for the whole, at the end of a process chain Surface treatment resulting layer system an improvement in corrosion protection and paint adhesion. In the illustration 1 are typical process chains summarized in the sense of the present invention, which benefit in particular from the pretreatment according to the invention.
The specifying designation of the pretreatment as "metallizing" is to be understood as meaning a pretreatment process which directly effects a metallic deposition of metal cations (A) on the zinc surface, wherein after metallizing pretreatment at least 50 at% of the element (A) corresponding to in the example part of this application defined analytical method on the zinc surface in the metallic state.
According to the invention, the redox potential E _redox is measured directly on average (1) on a metal electrode of the metal (A) in relation to a standard commercial reference electrode, eg silver-silver chloride electrode. For example, in an electrochemical measuring chain of the following type: $${\mathrm{e}}_{\mathrm{redox}}\mathrm{in\; volts}:\mathrm{Ag}/\mathrm{AgCl}/\mathrm{1}\mathrm{M\; KCl}//\mathrm{metal}\left(\mathrm{A}\right)/\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">M</figure-callout>}\left(\mathrm{1}\right)$$

• with Ag / AgCl / 1M KCl = 0.2368 V versus standard hydrogen electrode (SHE)
• with M (1) the agent (1) according to the invention containing cations and / or compounds of the metal (A) indicative

The same applies to the electrode potential E _Zn , which is determined at a zinc electrode in the middle (2), which differs from the agent (1) only by the absence of cations and / or compounds of the metal (A), compared to a standard commercial reference electrode: $${\mathrm{e}}_{\mathrm{Zn}}\mathrm{in\; volts}:\mathrm{Ag}/\mathrm{AgCl}/\mathrm{1}\mathrm{M\; KCl}//\mathrm{Zn}/\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="imgf0002.png"\; state="\{\{state\}\}">M</figure-callout>}\left(\mathrm{2}\right)$$

The method according to the invention is characterized in that a metallizing pretreatment of the zinc surface takes place when the redox potential E _{redox is more} anodic than the electrode potential E _Zn . This is the case when E _Redox -E _Zn > 0.

• mit M(1) das Mittel (1) enthaltend Kationen und/oder Verbindungen des Metalls (A) bezeichnend, und
• mit M(2) das Mittel (2) bezeichnend, welches sich von M(1) nur dadurch unterscheidet, dass es keine Kationen und/oder Verbindungen des Metalls (A) enthält.

As the electromotive force (EMF), ie as a thermodynamic driving force for the electroless metallizing pretreatment, the potential difference of redox potential E _redox and electrode potential E _Zn according to the above definitions is to be considered. The electromotive force (EMF) corresponds to an electrochemical measuring chain of the following type: $$\mathrm{Zn}/\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="imgf0002.png"\; state="\{\{state\}\}">M</figure-callout>}\left(\mathrm{2}\right)//\mathrm{metal}\left(\mathrm{A}\right)/\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">M</figure-callout>}\left(\mathrm{1}\right)$$

• denoting M (1) the agent (1) containing cations and / or compounds of the metal (A), and
• denoting M (2) the agent (2) which differs from M (1) only in that it contains no cations and / or compounds of the metal (A).

It is advantageous for the process according to the invention if the redox potential E _{redox of} the cations and / or compounds of the metal (A) in the aqueous medium (1) is at least +50 mV, preferably at least +100 mV and particularly preferably at least +300 mV, but at most +800 mV anodic than the electrode potential E _{Zn of} the zinc surface in contact with the aqueous agent (2). If the EMF is less than +50 mV, sufficient metallization of the galvanized surface can not be achieved in technically relevant contact times, so that in a subsequent passivating conversion treatment the metal deposit of the metal (A) is completely removed from the galvanized surface and the effect of the pretreatment therewith will be annulled. Conversely, an excessively high EMF of more than +800 mV in short times can lead to a complete and massive occupation of the galvanized surface with the metal (A), so that the desired formation of an inorganic corrosion-inhibiting and adhesion-promoting layer does not occur or at least in a subsequent conversion treatment is hindered. It is found that metallization is particularly effective when the concentration of cations and / or compounds of the metal (A) is at least 0.001M and preferably at least 0.01M, but does not exceed 0.2M, preferably 0.1M ,

Further, those cations and / or compounds of the metal (A) are preferable, which in the middle (1) both the electromotive force (EMF) condition as described above and having a standard potential E ⁰ _{Me of} the metal (A) which is more cathodic than the normal potential E ⁰ _{H2 of} the standard hydrogen electrode (SHE), preferably more than 100 mV, more preferably more than 200 mV more cathodic than the normal potential E ⁰ _H2 , wherein the standard potential E ⁰ _{Me of} the metal (A) refers to the reversible redox reaction Me ⁰ → Me ^{n +} + ne ^- in an aqueous solution of the metal cation Me ^{n +} with the activity 1 at 25 ° C.

If this second condition is not met, passivation layers are formed in a conversion treatment following the method according to the invention due to reduced pickling rates of the substrate surface, which layers are less homogeneous and have more defects. In the extreme case, the passivating conversion of the substrate surface pretreated in the process according to the invention is omitted in the subsequent process step. The same applies to an organic coating immediately following the pretreatment according to the invention, which is based on a self-deposition process which is initiated by the pickling attack of the substrate (autophoretic dip coating, abbreviation: AC for "autodepositable coating").

In the pretreatment process according to the invention, in order to increase the deposition rate of the cations and / or compounds of the metal (A), ie the metallization of the galvanized or alloy-galvanized surface, it is preferable to add accelerators with a reducing action to the aqueous agent (1). Suitable accelerators are oxo acids of phosphorus or nitrogen and their salts in question, wherein at least one phosphorus atom or nitrogen atom must be present in a middle oxidation state. Such accelerators are, for example, hyposalphous acid, hypo nitric acid, nitrous acid, hypophosphoric acid, hypodiphosphonic acid, diphosphorus (III, V) acid, phosphonic acid, diphosphonic acid and particularly preferably phosphinic acid and salts thereof.

Furthermore, it is possible to use accelerators known to the person skilled in the art in phosphating. In addition to their reduction properties, they also have depolarizing properties, ie they act as hydrogen scavengers, thus additionally favoring the metallization of the galvanized Steel surface. These include hydrazine, hydroxylamine, nitroguanidine, N-methylmorpholine N-oxide, glucoheptonate, ascorbic acid and reducing sugars.
The molar ratio of accelerator to the concentration of the cations and / or compounds of the metal (A) in the aqueous medium (1) is preferably not greater than 2: 1, more preferably not greater than 1: 1 and preferably not below 1: 5.

Optionally, the aqueous agent (1) in the process according to the invention additionally contain small amounts of copper (II) cations, which can also be deposited metallically on the galvanized surface simultaneously with the cations and / or compounds of the metal (A). However, it should be noted here that no massive, almost completely surface-covering cementation of copper occurs, since otherwise a subsequent conversion treatment is completely prevented and / or the paint adhesion deteriorates significantly. Therefore, the aqueous agent (1) should additionally contain not more than 50 ppm, preferably not more than 10 ppm, but at least 0.1 ppm of copper (II) cations.

In addition, the aqueous agent (1) for the metallizing pretreatment may additionally contain surfactants which are able to liberate the metallic surface from impurities without itself inhibiting the surface by forming compact adsorbate layers for the metallization. Nonionic surfactants with average HLB values of at least 8 and at most 14 may be used for this purpose.

The pH of the aqueous agent (1) is not smaller than 4 and not larger than 8, preferably not larger than 6.

For the pretreatment process according to the invention, which forms part of the process chain of the surface treatment of galvanized and / or alloy-galvanized steel surfaces, the application methods customary in strip steel production and strip steel finishing are practicable. These include, in particular, dipping and spraying processes. The contact time or pretreatment time with the aqueous agent (1) is at least 1 second, but is not longer than 30 seconds, preferably not longer than 10 seconds. Within this contact time result in inventive embodiment of the Process metallic coatings of the metal (A) with a coating of at least 1 mg / m ² , but not more than 50 mg / m ² . For the purposes of the present invention, the metallic layer support is defined as the area-related mass fraction of the element (A) on the galvanized or alloy-galvanized steel surface immediately after the pretreatment according to the invention.
Both the preferred contact times and layer conditions as well as the preferred application methods also apply to the pretreatment according to the invention of components assembled from a plurality of metallic materials insofar as these at least partially have zinc surfaces.

The present invention also includes those combinations of alloy-galvanized steel surfaces and aqueous compositions (1) in which an alloying constituent of the galvanized steel surface is the same element (A) as the metal (A) in the form of its cations and / or compounds in the aqueous medium (1). ,

The pretreatment process according to the invention is adapted to the subsequent process steps of the surface treatment of galvanized and / or alloy-galvanized steel surfaces with regard to optimized corrosion protection and outstanding paint adhesion, in particular to cut edges, surface defects and bimetallic contacts. Consequently, the present invention encompasses various aftertreatment processes, ie conversion and lacquer coatings, which, in conjunction with the pretreatment described above, provide the desired results in terms of corrosion protection. The illustration 1 illustrates various preferred within the meaning of the present invention process chains for corrosion-protective coating of metallic surfaces in automotive manufacturing, which are already begun at the steel producer ("Coil Industry") and continued and completed in the paint shop ("Paint Shop °) at the car manufacturer.
The invention therefore relates in a further aspect to the production of a passivating conversion coating on the metallized pretreated galvanized and / or alloy-galvanized steel surface with or without intermediate rinsing and / or drying step (US Pat. illustration 1 , Method IIa).

For this purpose, a chromium-containing or preferably chromium-free conversion solution can be used. Preferred conversion solutions with which the metal surfaces pretreated according to the present invention can be treated prior to the application of a permanent corrosion-protective organic coating can be used DE-A-199 23 084 and the literature cited herein. According to this teaching, a chromium-free aqueous conversion agent besides hexafluoro anions of Ti, Si and / or Zr may contain as further active ingredients: phosphoric acid, one or more compounds of Co, Ni, V, Fe, Mn, Mo or W, a water-soluble or water-dispersible film-forming organic polymer or copolymer and organophosphonic acids that have complexing properties. On page 4 of this document, a detailed list of organic film-forming polymers which may be included in said conversion solutions is given in lines 17-39.
Following this, this document discloses a very extensive list of complex-forming organophosphonic acids as further possible components of the conversion solutions. Concrete examples of these components may be mentioned DE-A-199 23 084 be removed.
Furthermore, water-soluble and / or water-dispersible polymeric complexing agents with oxygen and / or nitrogen ligands based on Mannich addition products of polyvinylphenols with formaldehyde and aliphatic amino alcohols may be present. Such polymers are in the patent US 5,298,289 disclosed.

The process parameters for a conversion treatment in the context of this invention, such as treatment temperature, treatment time and contact time are to be chosen such that a conversion layer is produced, the per m ² surface at least 0.05, preferably at least 0.2, but not more than 3, Contains 5, preferably not more than 2.0 and more preferably not more than 1.0 mmol of the metal M, which is the essential component of the conversion solution. Examples of metals M are Cr (III), B, Si, Ti, Zr, Hf. The coverage of the zinc surface with the metal M can be determined, for example, by an X-ray fluorescence method.

In a particular aspect of a process (IIa) according to the invention, which comprises a conversion treatment following the metallizing pretreatment, the chromium-free conversion medium additionally contains copper ions. The molar ratio of metal atoms M selected from zirconium and / or titanium to copper atoms in such a conversion agent is preferably chosen such that it produces a conversion layer in which at least 0.1, preferably at least 0.3, but not more than 2 mmol Copper are also included.

1. i) gegebenenfalls Reinigung / Entfettung der Werkstoffoberfläche
2. ii) metallisierende Vorbehandlung mit einem wässrigen Mittel (1) gemäß der vorliegenden Erfindung
3. iii) gegebenenfalls Spül- und/oder Trocknungsschritt
4. iv) chrom(VI)freie Konversionsbehandlung, bei der eine Konversionsschicht erzeugt wird, die pro m² Oberfläche 0,05 bis 3,5 mmol des Metalls M enthält, das die wesentliche Komponente der Konversionslösung darstellt, wobei die Metalle M ausgewählt sind aus Cr(III), B, Si, Ti, Zr, Hf.

The present invention thus also relates to a process (IIa) which comprises the following process steps, including the metallizing pretreatment and a conversion treatment of the galvanized and / or alloy-galvanized steel surface:

1. i) optionally cleaning / degreasing the material surface
2. ii) metallizing pretreatment with an aqueous agent (1) according to the present invention
3. iii) optionally rinsing and / or drying step
4. iv) chromium (VI) free conversion treatment in which a conversion layer containing, per m ^{2 of} surface area, 0.05 to 3.5 mmol of the metal M which is the essential component of the conversion solution, the metals M being selected from Cr (III), B, Si, Ti, Zr, Hf.

Alternatively, a method (IIa), in which the metallizing pretreatment is followed by a conversion treatment to form a thin amorphous inorganic coating, may also include a method (IIa). illustration 1 , IIb) in which the metallization of the invention is followed by zinc phosphating to form a crystalline phosphate layer having a preferred coating weight of not less than 3 g / m ² . However, preference is given in accordance with the present invention to a process (IIa) because of the significantly lower process outlay and the marked improvement in the corrosion protection of conversion layers on galvanized surfaces which have been previously metallized.

In addition, the metallizing pretreatment and the subsequent conversion treatment usually follow further process steps for the application of additional layers, in particular organic paints or coating systems ( illustration 1 , Method III-V).

1. a) als Hydroxylguppen-haltiger Polyether vorliegendes Epoxidharz auf Basis eines Bisphenol-Epichlorhydrin-Polykondensationsproduktes,
2. b) blockiertes aliphatisches Polyisocyanat,
3. c) nicht blockiertes aliphatisches Polyisocyanat,
4. d) mindestens eine Reaktionskomponente ausgewählt aus Hydroxylgruppen-haltigen Polyestern und Hydroxylgruppen-haltigen Poly(meth)acrylaten.

The present invention therefore relates in a further aspect to a process (III) which extends the process chain (i-iv) of process (II), wherein an organic coating agent (1) is applied, which dissolved or dispersed in an organic solvent or solvent mixture containing organic resin components, characterized in that the coating agent (1) contains at least the following organic resin components:

1. a) epoxy resin present as hydroxyl group-containing polyether based on a bisphenol-epichlorohydrin polycondensation product,
2. b) blocked aliphatic polyisocyanate,
3. c) unblocked aliphatic polyisocyanate,
4. d) at least one reaction component selected from hydroxyl-containing polyesters and hydroxyl-containing poly (meth) acrylates.

Component a) is a fully reacted polycondensation product of epichlorohydrin and a bisphenol. This essentially has no epoxide groups as reactive groups more. The polymer is then in the form of a hydroxyl-containing polyether, which can undergo crosslinking reactions with, for example, polyisocyanates via these hydroxyl groups.

The bisphenol component of this polymer can be selected, for example, from bisphenol A and bisphenol F. The average molar mass (according to the manufacturer, for example determinable by gel permeation chromatography) is preferably in the range from 20,000 to 60,000, in particular in the range from 30,000 to 50,000. The OH number is preferably in the range from 170 to 210 and in particular in the range from 180 to 200. In particular, polymers are preferred whose hydroxyl content based on the Estherharz in the range of 5 to 7 wt .-%.

The aliphatic polyisocyanates b) and c) are preferably based on HDI, in particular on HDI trimer. As blocking agents in the blocked aliphatic polyisocyanate b), the customary polyisocyanate blocking agents may be used. Examples which may be mentioned are: butanone oxime, dimethylpyrazole, malonic esters, diisopropylamine / malonic esters, diisopropylamine / triazole and ε-caprolactam. Preferably, a combination of malonic ester and diisopropylamine is used as the blocking agent.
The content of blocked NCO groups of component b) is preferably in the range from 8 to 10% by weight, in particular in the range from 8.5 to 9.5% by weight. The equivalent weight is preferably in the range of 350 to 600, in particular in the range of 450 to 500 g / mol.

The non-blocked aliphatic polyisocyanate c) preferably has an equivalent weight in the range of 200 to 250 g / mol and an NCO content in the range of 15 to 23 wt%. For example, an aliphatic polyisocyanate can be selected which has an equivalent weight in the range of 200 to 230 g / mol, in particular in the range of 210 to 220 g / mol and an NCO content in the range of 18 to 22 wt .-%, preferably in the range from 19 to 21% by weight. Another suitable aliphatic polyisocyanate has for example an equivalent weight in the range of 220 to 250 g / mol, in particular in the range of 230 to 240 g / mol and an NCO content in the range of 15 to 20 wt .-%, preferably in the range of 16 , 5 to 19 wt .-%. Each of these aliphatic polyisocyanates mentioned may be component c). However, a mixture of these two polyisocyanates can also be present as component c). If a mixture of the two mentioned polyisocyanates is used, the ratio of the first-mentioned polyisocyanate to the last-mentioned polyisocyanate for component c) is preferably in the range from 1: 1 to 1: 3.

Component d) is selected from hydroxyl-containing polyesters and hydroxyl-containing poly (meth) acrylates. For example, a hydroxyl-containing poly (meth) acrylate having an acid number in the range of 3 to 12, in particular in the range of 4 to 9 mg KOH / g can be used. The content of hydroxyl groups is preferably in the range of 1 to 5 and in particular in the range of 2 to 4 wt .-%. The equivalent weight is preferably in the range of 500 to 700, in particular in the range of 550 to 600 g / mol.

If a hydroxyl-containing polyester is used as component d), a branched polyester having an equivalent weight in the range from 200 to 300, in particular in the range from 240 to 280 g / mol, can be selected for this purpose. Furthermore, for example, a weakly branched polyester having an equivalent weight in the range of 300 to 500, in particular in the range of 350 to 450 g / mol is suitable. These different types of polyester can each individually or as a mixture form the component d). Of course, a mixture of hydroxyl-containing polyesters and hydroxyl-containing poly (meth) acrylates may also be present as component d).

The coating composition (1) in process (III) according to the invention thus contains both a blocked aliphatic polyisocyanate b) and an unblocked aliphatic polyisocyanate c). As potential reaction components for these two types of polyisocyanate, the hydroxyl-containing components a) and d) are available. Possible reaction of each of components a) and d) with each of components b) and c) produces a complex polymer network of polyurethanes during curing of the agent (2). In addition, in the case where hydroxyl-containing poly (meth) acrylates are used as component d), further crosslinking via the double bonds of these components occur. Insofar as not all double bonds of the poly (meth) acrylates crosslink during curing, especially double bonds present on the surface can bring about improved bonding to a subsequently applied lacquer, if it also contains components with polymerizable double bonds. From this point of view, it is preferred that component d) consists at least partially of hydroxyl-containing poly (meth) acrylates.

When the coating composition (1) is cured in the process (III) according to the invention, it is to be expected that initially the non-blocked aliphatic polyisocyanate c) reacts with one or both of components a) and d). If the hydroxyl groups of the components d) are more reactive than those of the component a), during curing, first of all, a reaction of the component c) with the component d) occurs.

• a) : b) = 1: 0,8 bis 1 : 1,3
• c) : d)=1 ; 1,4 bis 1 : 2,3

Die Komponenten a) und d) einerseits sowie b) und c) andererseits liegen vorzugsweise in folgendem relativen Gewichtsverhältnis vor:

1. a) : d) = 1 : 2 bis 1: 6 und (vorzugsweise 1 : 3 bis 1 : 5)
2. b) : c) = 1 : 0,5 bis 1 : 5 (vorzugsweise 1 : 1 bis 1 : 3).

In contrast, the blocked aliphatic polyisocyanate b) only reacts with one or both of the components a) and d) when the deblocking temperature is reached. For polyurethane formation is then only that of the reactants a) and d) to Available, which has the less reactive OH groups. For the forming polyurethane network, this means, for example, that when the OH groups of components a) are less reactive than those components d), two polyurethane networks from the reaction of components c) and d) on the one hand and the components a) and b) on the other.
The coating composition (1) in process (III) according to the invention comprises components a) and b) on the one hand and c) and d) on the other hand preferably in the following relative weight ratios:

• a): b) = 1: 0.8 to 1: 1.3
• c): d) = 1; 1.4 to 1: 2.3

The components a) and d) on the one hand and b) and c) on the other hand are preferably present in the following relative weight ratio:

1. a): d) = 1: 2 to 1: 6 and (preferably 1: 3 to 1: 5)
2. b): c) = 1: 0.5 to 1: 5 (preferably 1: 1 to 1: 3).

Preferred absolute ranges of the said four components a) to d) are given below since these are based on the density of optionally present conductive pigments ( illustration 1 , Method IIIb). Preferably, the coating composition (1) contains, in addition to the components a) to d), a conductive pigment or a mixture of conductive pigments. These may have a relatively low density, such as carbon black and graphite, or a relatively high density, such as metallic iron. The absolute content of the coating composition (1) of the conductivity pigments depends on their density, since it depends less on the mass fraction than on the volume fraction of the conductive pigment in the cured coating for the effect as a conductive pigment.

In general, the coating composition (1), based on the total mass of the composition, contains (0.8 to 8) × ρ% by weight of conductive pigment, where ρ is the density of the conductive pigment or the average density of the mixture of conductive pigments in g / cm ² means. The coating composition (1) preferably contains (2 to 6), based on its total mass, ρ% by weight of conductive pigment.

For example, if the coating composition (1) contains only graphite having a density of 2.2 g / cm ² as the conductive pigment, then it preferably contains at least 1.76, in particular at least 4.4, and preferably not more than 17 , 6, in particular not more than 13.2 wt .-% graphite. If iron powder having a density of 7.9 g / cm ^{2 is used} as sole conductive core pigment, the coating composition (1), based on its total mass, preferably contains at least 6.32, in particular at least 15.8% by weight and not more than 63 , 2, in particular not more than 47.4% by weight. The proportions by weight are calculated accordingly if, for example, exclusively MoS ₂ having a density of 4.8 g / cm 3 as the conductive pigment, aluminum having a density of 2.7 g / cm ³ or zinc with a density of 7.1 g / cm ³ is used.

However, a favorable combination of properties may occur if the coating composition (1) contains not only a single conductive pigment but a mixture of at least two conductive pigments, which then differ greatly in their density. For example, a mixture can be used in which the first mixing partner is a light conductive pigment such as carbon black, graphite or aluminum and the second partner of the mixture is a heavy conductive pigment such as zinc or iron. In these cases, for the density ρ in the aforementioned formula, the average density of the mixture is used, which can be calculated from the weight percentages of the components in the mixture and from their respective density.

Accordingly, a specific embodiment of a coating composition (1) in process (IIIb) is characterized in that it contains both a conductive pigment having a density of less than 3 g / cm ³ and a conductive pigment having a density of greater than 4 g / cm ³ , Wherein the total amount of conductive pigment, based on the total mass of the composition (2), is (0.8 to 8) × ρ% by Weight, Where ρ is the average density of the mixture of the conductive pigments in g / cm ³ .

For example, the coating agent (1) as a conductive pigment, a mixture of carbon black or graphite on the one hand and iron powder on the other hand. On the other hand, the weight ratios of carbon black and / or graphite on the one hand and iron on the other hand can be in the range from 1: 0.1 to 1:10, in particular in the range from 1: 0.5 to 1: 2.

The coating composition (1) may therefore contain aluminum flakes, graphite and / or carbon black as a light electrically conductive pigment. The use of graphite and / or carbon black is preferred. Carbon black, and especially graphite, not only provide electrical conductivity of the resultant coating, but also contribute to this layer having a desirable low Mohs hardness of not more than 4 and being readily reshapeable. In particular, the lubricating effect of graphite contributes to a reduced wear of the forming tools. This effect can be further promoted by additionally using pigments with a lubricating effect such as molybdenum sulfide with. As further lubricants or forming aids, the coating agent (1) may contain waxes and / or Teflon.

The electrically conductive pigment having a specific weight of at most 3 g / cm ³ may be in the form of small spheres or aggregates of such spheres. It is preferred that the balls or the aggregates of these balls have a diameter of less than 2 microns. However, these electrically conductive pigments are preferably in the form of platelets whose thickness is preferably less than 2 μm.

The coating composition (1) in process (III) according to the invention comprises at least the resin components described above and also solvents. The resin components a) to d) are usually present in their commercial form as a solution or dispersion in organic solvents. The coating composition (1) prepared therefrom then also contains these solvents.

These are desirable in order, in spite of the additional presence of the electrically conductive pigment such as, for example, graphite and optionally further pigments such as, in particular, anticorrosive pigments to set a viscosity which allows the coating agent (1) to be applied to the substrate in the coil coating process. If necessary, additional solvent can be added. The chemical nature of the solvents is usually dictated by the choice of raw materials containing the appropriate solvent. For example, the following may be present as solvents: cyclohexanone, diacetone alcohol, diethylene glycol monobutyl ether acetate, diethylene glycol, propylene glycol methyl ether, propylene glycol n-butyl ether, methoxypropyl acetate, n-butyl acetate, Xylene, dimethyl glutarate, dimethyl adipate and / or dimethyl succinate.

The preferred proportion of solvent on the one hand and organic resin components on the other hand in the coating agent (1), expressed in% by weight, depends on the content of conductive pigment in% by weight in the coating agent (1). The higher the density of the conductive pigment, the higher its preferred weight ratio of the total coating agent (1), and the lower the weight proportions of solvent and resin components. The preferred weight percentages of solvent and resin components therefore depend on the density ρ of the conductivity pigment used or the average density ρ of a mixture of conductive pigments.

In general, for the coating composition (1) in the process (III) according to the invention, it is preferable that, based on the total mass of the coating composition (1), [(25 to 60). Adjustment factor] wt%, preferably [(35 to 55) adjustment factor] wt% organic solvent and [(20 to 45) adjustment factor] wt%, preferably [(25 to 40) adjustment factor] wt. % organic resin components, wherein the sum of the weight percentages of organic resin component and solvent is not greater than [93 - adjustment factor] wt%, preferably not greater than [87 * adaptation factor] wt%, and wherein the adjustment factor [100 -2,8ρ]: 93.85 and ρ is the density of the conductive pigment or the average density of the mixture of conductive pigments in g / cm ³ .

With regard to the individual resin component a), it is preferable that the coating agent (1), based on the total mass of the coating agent (1), [(2 to 8) adjustment factor] wt .-%, preferably [(3 to 5) adjustment factor] wt. % of the resin component a), wherein the adjustment factor is [100-2.8ρ]: 93.85 and ρ is the density of the conductive pigment or the average density of the mixture of conductive pigments in g / cm ³ . From the proportion of the resin component a) can be calculated with the above-mentioned preferred ratios of the individual resin components, the preferred proportions of the resin components b) to d) in the coating agent (1). For example, the proportion of components b) in the total mass of the coating agent [(2 to 9) adjustment factor] wt .-%, Preferably, [(3 to 6) adjustment factor] wt .-%, the proportion of resin components c) [(4 to 18) adjustment factor] wt .-%, preferably [(6 to 12) adjustment factor] wt.% And the proportion of Resin Components d) [(7 to 30) Adjustment Factor] wt%, preferably [(10 to 20) Adjustment Factor] wt%. The "adaptation factor" has the meaning given above.
Furthermore, it is preferred that the layer b) additionally contains corrosion inhibitors and / or anticorrosive pigments. Corrosion inhibitors or anticorrosive pigments which are known in the prior art for this purpose can be used here. Examples which may be mentioned are: magnesium oxide pigments, in particular in nanoscale form, finely divided and very finely divided barium sulfate or anticorrosive pigments based on calcium silicate. The preferred weight fraction of the anticorrosion pigments on the total mass of the coating composition (1) in turn depends on the density of the anticorrosion pigments used. Preferably, the coating composition (1) in the process (III) according to the invention, based on the total mass of the coating composition, contains [(5 to 25). Adjustment factor] wt .-%, in particular [(10 to 20). Adjustment factor] wt% anticorrosive pigment, where the adjustment factor is [100-2.8ρ]: 93.85 and ρ is the density of the conductive pigment or the average density of the mixture of conductive pigments in g / cm ³ .

The mechanical and chemical properties of the coating obtained after the baking of the coating agent (1) in process (III) according to the invention can be further improved by additionally containing fillers. For example, these may be selected from silicas or silicas (optionally hydrophobed), alumina (including basic alumina), titania and barium sulfate. With regard to their preferred amounts, the coating composition (1) is [(0.1 to 3). Adjustment factor] wt .-%, preferably [(0.4 to 2) adjustment factor] wt .-% filler selected from silicas or silicon oxides, aluminum oxides, titanium dioxide and barium sulfate, wherein the adjustment factor [100-2.8 p]: 93 , 85 and ρ means the density of the conductive pigment or the average density of the mixture of conductive pigments in g / cm ³ .

1. i) gegebenenfalls Reinigung / Entfettung der Werkstoffoberfläche
2. ii) metallisierende Vorbehandlung mit einem wässrigen Mittel (1) gemäß der vorliegenden Erfindung
3. iii) gegebenenfalls Spül- und/oder Trocknungsschritt
4. iv) chrom(VI)freie Konversionsbehandlung, bei der eine Konversionsschicht erzeugt wird, die pro m² Oberfläche 0,01 bis 0,7 mmol des Metalls M enthält, das die wesentliche Komponente der Konversionslösung darstellt, wobei die Metalle M ausgewählt sind aus Cr(III), B, Si, Ti, Zr, Hf.
5. v) gegebenenfalls Spül- und/oder Trocknungsschritt
6. vi) Beschichtung mit einem Beschichtungsmittel (1) gemäß vorstehender Beschreibung und Aushärten bei einer Substrattemperatur im Bereich von 120 bis 260 °C, vorzugsweise im Bereich von 150 bis 170 °C.

If lubricants or forming aids are additionally used, it is the case that the coating composition (1), based on its total mass, lubricants or forming aids, preferably selected from waxes, molybdenum sulfide and Teflon, preferably in an amount of [(0.5 to 20). Adjustment factor], in particular in an amount of [(1 to 10) adjustment factor] wt%, where the adjustment factor is [100-2,8ρ]: 93.85 and ρ is the density of the conductive pigment or the average density of the mixture of conductive pigments in g / cm ³ .
The process (III) according to the invention, which comprises the application of organic paints, accordingly consists of the following process chain:

1. i) optionally cleaning / degreasing the material surface
2. ii) metallizing pretreatment with an aqueous agent (1) according to the present invention
3. iii) optionally rinsing and / or drying step
4. iv) chromium (VI) free conversion treatment which produces a conversion layer containing, per m ^{2 of} surface, 0.01 to 0.7 mmol of the metal M which is the essential component of the conversion solution, the metals M being selected from Cr (III), B, Si, Ti, Zr, Hf.
5. v) optionally rinsing and / or drying step
6. vi) coating with a coating agent (1) as described above and curing at a substrate temperature in the range of 120 to 260 ° C, preferably in the range of 150 to 170 ° C.

In this case, preferably all steps (i-vi) are carried out as a strip treatment method, wherein the liquid coating composition (1) is applied in step (vi) in such an amount that, after curing, the desired layer thickness is in the range from 0.5 to 10 Preferably, therefore, the coating agent (1) is applied in the so-called coil coating process. Here, continuous metal strips are continuously coated. The coating agent (1) can be applied by different methods, which are familiar in the prior art. For example, applicator rolls can be used to directly adjust the desired wet film thickness. Alternatively, one can immerse the metal strip in the coating agent (1) or spray it with the coating agent (1), after which the desired wet film thickness is adjusted by means of squeeze rolls.

If metal strips coated immediately before with a metal coating, for example with zinc or zinc alloys, electrolytically or by hot dip coating, it is not necessary to clean the metal surfaces prior to performing the metallizing pretreatment (ii). However, if the metal strips have already been stored and in particular provided with corrosion protection oils, a purification step (i) is necessary before carrying out step (ii).

After applying the liquid coating agent (1) in step (vi), the coated sheet is heated to the required drying or crosslinking temperature for the organic coating. The heating of the coated substrate to the required substrate temperature ("peak-metal-temperature" = TMP) in the range of 120 to 260 ° C, preferably in the range of 150 to 170 ° C can take place in a heated continuous furnace. However, the treatment agent can also be brought to the corresponding drying or crosslinking temperature by infrared radiation, in particular by near infrared radiation.

Such pre-coated metal sheets are tailored and converted in the automotive production for the production of bodies accordingly. The assembled component or the assembled body shell therefore has unprotected edges, which must be treated in addition corrosion protection. In the so-called "paint shop", therefore, there is a further corrosion-protective treatment and, ultimately, the realization of the automobile-typical paint structure.

The present invention therefore relates, in a further aspect, to a process (IV) which extends the process chain (i-vi) of process (III), wherein a crystalline phosphate layer is first deposited on the exposed metal surfaces, in particular on the cut edges, in order to subsequently to provide a final corrosion protection by means of dip paint, in particular protection against infiltration of the paint system at the cutting edges. In the event that the first coating in process (III) leads to a conductive coating with an organic coating agent (1), the entire metallic component including the phosphated cut edges and the first-coated surfaces in process (III) can be electrodeposited ( illustration 1 , Method IVb). at Insufficient conductivity of the initial coating, the phosphated cutting edges are exclusively electrocoated, without a further paint build on the erstbeschichteten surfaces is realized. The same applies if the cut edges are not phosphated, but coated with a self-depositing dip (AC) ( illustration 1 , Method IVc). However, the present invention is distinguished by the fact that the zinc surfaces pretreated in a metallizing manner according to the invention in particular excellently prevent edge corrosion. In a process chain according to the invention, which comprises the electrodeposition coating (KTL, ATL) in process (IV) and the application of further paint layers in a process (V), therefore, the amount of deposited dip paint per m ^{2 of} the component consisting of zinc surfaces pretreated according to the invention (US Pat. illustration 1 , Method I) and / or the amount of filler to be applied, which has the main task of protecting the body panels against stone chipping and compensate for any unevenness of the metal surface, in the secondary coating ( illustration 1 , Method V) are significantly reduced, without a loss of performance in terms of corrosion protection and paint adhesion is the result.

In a further aspect, the present invention relates to the galvanized and / or alloy-galvanized steel surface and the metallic component, which consists at least partially of a zinc surface which has been pretreated by metallizing in accordance with the process according to the invention with the aqueous agent (1) or subsequently this pretreatment with further passivating Conversion layers and / or paints, for example according to the inventive method (II-IV) coated.
Such a treated steel surface or treated component is used in body construction in automotive manufacturing, shipbuilding, construction and for the production of white goods.

Claims (14)

1. A method for the metallizing pretreatment of galvanized or alloy-galvanized steel surfaces, wherein the galvanized or alloy-galvanized steel surface is brought into contact with an aqueous agent (1) for at least 1 second, but not longer than 30 seconds, the pH value of which is not less than 4 and not greater than 8, wherein cations and/or compounds of a metal (A) are contained in the agent (1), the redox potential E_Redox of which cations and/or compounds of the metal (A) measured at a metal electrode of the metal (A) at a specified method temperature and concentration of cations and/or compounds of the metal (A) in the aqueous agent (1) is more anodic than the electrode potential E_Zn of the galvanized or alloy-galvanized steel surface in contact with an aqueous agent (2) that differs from the agent (1) only in that the agent (2) does not contain cations and/or compounds of the metal (A), characterized in that the cations and/or compounds of the metal (A) in the agent (1) are selected from cations and/or compounds of tin in the oxidation states +II and/or +IV and, after the galvanized or alloy-galvanized steel surface has been brought into contact with the aqueous agent, a metallic plating with metal (A) is present in a coating of at least 1 mg/m², but not more than 50 mg/m².
2. The method according to claim 1, characterized in that the redox potential E_Redox of the cations and/or compounds of the metal (A) in the aqueous agent (1) is more anodic than the electrode potential E_Zn of the galvanized or alloy-galvanized steel surface in contact with the aqueous agent (2) by at least +50 mV, preferably at least +100 mV, and especially preferably at least +300 mV, but at most +800 mV.
3. The method according to one or both of claims 1 and 2, characterized in that the concentration of cations and/or compounds of the metal (A) is at least 0.001 M and preferably at least 0.01 M, but does not exceed 0.2 M, preferably 0.1 M.
4. The method according to one or more of the preceding claims, characterized in that the pH value of the aqueous agent is not greater than 6.
5. The method according to one or more of claims 1 to 4, characterized in that the aqueous agent additionally contains accelerators selected from oxoacids of phosphorus or nitrogen and salts thereof, wherein at least one phosphorus atom or nitrogen atom is present in an average oxidation state.
6. The method according to one or more of claims 1 to 4, characterized in that the aqueous agent additionally contains accelerators selected from hydrazine, hydroxylamine, nitroguanidine, N-methylmorpholine-N-oxide, glucoheptonate, ascorbic acid, and reductive sugars.
7. The method according to one or both of claims 5 to 6, characterized in that the molar ratio of accelerator to the concentration of the cations and/or compounds of the metal (A) is not greater than 2:1, preferably not greater than 1:1, but is not below 1:5.
8. The method according to one or more of claims 1 to 7, characterized in that the aqueous agent additionally contains not more than 50 ppm, preferably not more than 10 ppm, but at least 0.1 ppm, of copper(II) cations.
9. The method according to one or more of claims 1 to 8, characterized in that the aqueous agent additionally contains surfactants.
10. The method according to one or more of claims 1 to 9, characterized in that the galvanized or alloy-galvanized steel surface is brought into contact with the aqueous agent for not longer than 10 seconds.
11. The method according to one or more of claims 1 to 10, characterized in that, after the galvanized or alloy-galvanized steel surface has been brought into contact with the aqueous agent, a passivating conversion treatment of the galvanized or alloy-galvanized steel surface pretreated in a metallizing manner occurs with or without an intermediate rinsing and/or drying step.
12. The method according to claim 11, characterized in that further steps for applying additional layers, particularly organic paints or paint systems, follow.
13. A metallic component, consisting at least partially of a galvanized or alloy-galvanized steel surface metallized according to one or more of claims 1 to 10.
14. The metallic component according to claim 13, characterized in that further layers, particularly conversion layers and/or paints, are applied.

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