EP1678344B1 - Essentially chromium-free method for passivating metallic surfaces consisting of zn, zn alloys, al or al alloys - Google Patents

Abstract

The present invention relates to a substantially chromium-free process for passivating metallic surfaces of Zn, Zn alloys, Al or Al alloys by treating the surface with an acidic aqueous formulation which comprises at least one substantially noncrosslinked, water-soluble polymer or copolymer containing at least 50% by weight of (meth)acrylic acid units and comprises water or an aqueous solvent mixture comprising at least 50% by weight of water, and by further treating the surface with at least one water-soluble crosslinker comprising at least 2 crosslinking groups selected from the group consisting of azirane, oxirane, and thiirane groups. The invention further relates to passivating layers obtainable by means of the process and to a formulation suitable for this process.

Description

The present invention relates to a substantially chromium-free process for passivating metallic surfaces of Zn, Zn alloys, Al or Al alloys by treating the surface with an acidic, aqueous preparation containing at least one substantially uncrosslinked, water-soluble polymer or copolymer at least 50% by weight of (meth) acrylic acid units, as well as water or an aqueous solvent mixture containing at least 50% by weight of water, and by additionally treating the surface with at least one water-soluble crosslinker containing at least 2 crosslinking groups selected from the group of azirane. , Oxirane or thiirane groups. The invention further relates to passivation layers obtainable by the process and to a preparation suitable for this process.

The corrosion protection treatment of modern metallic materials usually takes place in multi-stage processes, and the surface of treated metals has several different layers.

The protection of metallic components against corrosion has great economic importance. At the same time, the requirements for corrosion protection are becoming ever higher. By way of example, it should be noted that with newer car types nowadays up to 12 years warranty against rust through are granted.

Particularly important technically and economically is the corrosion protection treatment of aluminum surfaces and the surfaces of galvanized metals, in particular of galvanized or hot-dip galvanized iron or steel. The corrosion protection of zinc is based on the fact that it is less noble than the metallic material itself and therefore first itself corroded. The metallic material itself remains intact as long as it is still covered with zinc throughout.

In the presence of atmospheric oxygen, on the surface of Zn or Zn alloys, Al or Al alloys, a thin oxide layer initially forms, which more or less slows down the corrosive attack on the underlying metal, depending on the external conditions.

In order to enhance the protective effect of such an oxide layer, Al and Zn surfaces are usually subjected to an additional passivation treatment. In the course of such a treatment, a part of the metal to be protected dissolves, and is then immediately re-incorporated into an oxide film on the metal surface. This movie is similar to the already existing oxide film but offers one stronger protection. It is commonly referred to as a passivation layer. It also often improves the adhesion of paint coatings applied to the metal. Instead of the term "passivation layer", the term "conversion layer" is therefore often used interchangeably, sometimes also the term "pretreatment layer". Passivation layers are comparatively thin and usually have a thickness of not more than 3 μm.

To enhance the corrosion protection, additional (paint) layers are generally applied to the passivation layer. Usually it is a combination of several layers of paint, each serving different purposes. They serve, for example, to protect the passivation layer and the metal from corrosive gases and / or liquids but also from mechanical damage, such as rockfall, and of course also aesthetic purposes. Coating layers are usually much thicker than passivation layers. Typical thicknesses range from 5 μm to 400 μm. The use of crosslinkers with azirane, oxirane or thiirane groups in coating materials, paints or the like is known, for example from WO 01/30513 . JP-A 2002/327096 . JP-A 2003/027254 and JP-A 2002/326310 , However, as shown above, a paint or coating is clearly distinguishable from a passivation.

The passivation can be used for permanent corrosion protection or even for temporary corrosion protection. A temporary protection is used, for example, only for storing or transporting a metal sheet or other metallic workpiece and removed again before the final processing.

Heretofore, passivation layers on zinc or aluminum surfaces have usually been obtained by treating the workpiece to be protected with aqueous, acidic solutions of CrO ₃ . The mechanism of such passivation is complex. Among other things, metallic Zn or Al is released from the surface and precipitates again in the form of amorphous zinc chromium oxides or aluminum chromium oxides. However, the layers may also contain foreign ions and / or further components from the treatment solution. In particular, in the case of treatment with chromic acid, it can not be avoided that a certain amount of Cr (VI) is also incorporated into the passivation layer.

In order to avoid treatment with carcinogenic Cr (VI) solutions, treatments with acidic, aqueous Cr (III) solutions have been proposed. For example, be on US 4,384,902 or WO 97/40208 directed. However, there are increasing numbers of customers in the market who desire completely chrome-free passivation processes. To avoid the use of Cr (VI) such as Cr (III), therefore, the use of polymers is becoming increasingly important.

Chromium-free passivation processes using organic polymers are known in principle.

DE-A 195 16 765 discloses a chromium and fluoride-free process for forming conversion coatings on Zn or Al metallic surfaces. The acidic solution used for passivation comprises a water-soluble polymer, phosphoric acid and Al chelate complexes. The use of crosslinkers for passivation is not disclosed.

DE-A 197 54 108 discloses a chromium-free aqueous corrosion inhibitor comprising hexafluoro anions of Ti (IV) and / or Zr (IV), vanadium ions, cobalt ions and phosphoric acid. Optionally, still further different film-forming polymers can be added. The use of crosslinkers is not disclosed.

DE-A 199 23 084 discloses a chromium-free aqueous corrosion inhibitor containing hexafluoro anions of Ti (IV), Si (IV) and / or Zr (IV), an organophosphonic acid, and a water-soluble or water-dispersible, film-forming organic polymer or copolymer. Acrylic acid and methacrylic acid are disclosed as polymeric binders in addition to a large number of other polymers. Furthermore, the use of urea derivatives, epoxy resins, (blocked) polyisocyanates or their oligomeric derivatives as crosslinkers is disclosed. However, epoxy resins based on bisphenol A or F units and epichlorohydrin are not water soluble. In the preferred embodiment of DE-A 199 23 084 For example, a (meth) acrylate dispersion is optionally used in combination with an epoxy resin. However, dispersions are generally less well suited than homogeneous solutions, since on the one hand the dispersion aids and surfactants present in dispersions can be troublesome and furthermore the low viscosity enables only a very poor film thickness adjustment. Homogeneous systems are easier to handle, because the viscosity can be easily adjusted by the content of the solvent. The combination of a water-soluble polymer with more than 50% by weight of (meth) acrylic acid units with a water-soluble crosslinker is known in DE-A 199 23 084 not revealed.

EP-A 787 830 discloses a chromium-free metal surface treatment composition comprising an OH group-containing organic resin, phosphoric acid, and at least one metal ion, for example, Co, Cu, Fe, Mn, Sn, or V. The examples also disclose copolymers comprising acrylic acid and / or methacrylic acid units. However, the amount of (meth) acrylic acid units in the copolymers is in each case well below 50 wt.%. In addition, especially acrylates are used as comonomers. The disclosed copolymers are not homogeneous water-soluble polymers. The Scripture also mentions optionally the use of epoxy crosslinkers. The combination of a water-soluble polymer with However, more than 50% by weight of (meth) acrylic acid units with a water-soluble crosslinker is not disclosed.

JP-A 56-000279 discloses a Cr-free process for surface treatment in which the surface of Zn or galvanized steel is treated with an aqueous solution of a polyamine and a metal salt of phytic acid. The use of crosslinkers is not disclosed.

In our still unpublished application DE 103 07 973.4 describes the use of carboxylate-rich polymers for the passivation of metals. The use of crosslinkers is not disclosed.

In addition to achieving very good corrosion protection, a chromium-free passivation process must also meet a number of process engineering requirements.

For example, passivation is carried out by immersing the workpieces to be passivated in a passivating solution. Loose workpieces (eg screws) can be filled into a drum and the drum submerged. Larger workpieces can also be mounted on a suitable frame and the frame dipped. In the dipping method, the contact time between the passivating solution and the workpiece can be determined comparatively freely by the person skilled in the art, and thus quite thick passivation layers can also be obtained. The contact time can be in the range of minutes. In this technique, more complex workpieces are usually first joined together, for example, welded together from steel parts and galvanized and passivated therein as a whole.

For the production of flat metal workpieces such as automotive parts, body panels, equipment panels, cladding, ceiling panels or window profiles metal sheets are formed by means of suitable techniques such as punching, drilling, folding, profiling and / or deep drawing. Larger components, such as automobile bodies are optionally joined together by welding several items. The raw material for this purpose are usually long metal strips, which are produced by rolling the metal and wound into rolls ("coils") for storage and transport.

The galvanizing and passivation of such metal strips is made on a large scale in continuous systems. The metal strip is first driven for galvanizing by a device for galvanizing, for example a trough with molten zinc, and then directly on through a further device for passivation, for example, also a tub or a flushing device. As a rule, will be still further process steps continuously made, for example, cleaning or rinsing steps or the application of a first coat of paint on the passivation layer. Typical speeds at which metal belts are driven through the continuous systems are 50 to 100 m / min. This means that the contact time between the metallic surface and the preparation used for passivation is only short. Usually only a few seconds are available to treat. An industrially suitable process must therefore still have sufficient results with only short contact times.

The object of the invention was therefore to provide an improved, substantially Cr-free method for passivating metallic surfaces of Zn, Zn alloys, Al or Al alloys, which offers improved corrosion protection over the prior art and in which Nevertheless, a satisfactory result requires only short contact times between the metallic surface and the preparation used for passivation. In particular, the method should also be able to be carried out continuously.

1. (a) mindestens ein im wesentlichen unvernetztes, wasserlösliches Polymer oder Copolymer (A), welches mindestens 50 Gew. % (Meth)acrylsäureeinheiten umfasst, sowie
2. (b) Wasser oder ein mindestens 50 Gew. % Wasser enthaltendes, wässriges Lösemittelgemisch (B) umfasst,

und man die Oberfläche weiterhin mit mindestens einem wasserlöslichen Vernetzer behandelt, wobei der Vernetzer mindestens 2 vernetzende Gruppen, ausgewählt aus der Gruppe von Aziran-, Oxiran- oder Thiirangruppen umfasst, welche mittels einer mindestens 2 C-Atome umfassenden, verknüpfenden Gruppe (X) miteinander verbunden sind das zahlenmittlere Molekulargewicht M_n des Vernetzers 112 bis 5000 g/mol beträgt, die löslichkeit des Vernetzers in Wasser mindestens 10g/l beträgt, und man die Behandlung mit dem Vernetzer vor, nach oder gleichzeitig mit der Behandlung mit der Zubereitung (Z) vornimmt.Accordingly, a substantially chromium-free process has been found for passivating metallic surfaces of Zn, Zn alloys, Al or Al alloys comprising contacting the surface of the metal with an acidic aqueous preparation of a polymer containing -COOH groups and / or the salts thereof, treated, wherein the used for the treatment preparation (Z) at least

1. (A) at least one substantially uncrosslinked, water-soluble polymer or copolymer (A) which comprises at least 50% by weight of (meth) acrylic acid units, and
2. (b) water or an aqueous solvent mixture (B) comprising at least 50% by weight of water,

and further treating the surface with at least one water-soluble crosslinker, wherein the crosslinker comprises at least 2 crosslinking groups selected from the group of azirane, oxirane or thiirane groups which are linked together by means of a linking group (X) comprising at least 2 C atoms the number average molecular weight M _{n of} the crosslinker is 112 to 5000 g / mol, the solubility of the crosslinker in water is at least 10 g / l, and the treatment with the crosslinker before, after or simultaneously with the treatment with the preparation (Z) performs.

In a preferred embodiment of the invention, the metallic surface is the surface of a band metal, and more preferably, the passivation is carried out by means of a continuous process.

The invention further relates to a passivation layer on a metallic surface of Zn, Zn alloys, Al or Al alloys obtainable by the process, metallic surfaces comprising such a passivation layer and a preparation for passivation.

More specifically, the following is to be accomplished for the invention:

The term "substantially chromium-free" in the sense of this invention means that the actual passivating effect is caused by the polymer used in combination with the crosslinker and optionally further components of the preparation. However, it should not be excluded that small amounts of chromium compounds could be added for fine control of the properties of the passivation layer. The amount should, however, not exceed 10% by weight, preferably 5% by weight and more preferably 2% by weight, relative to the amount of polymer used and crosslinker together, moreover a content of 2% by weight, preferably 1% by weight and especially preferably 0.5 wt.% Chromium should not be exceeded with respect to all constituents of the composition. If chromium compounds are to be used, Cr (III) compounds should preferably be used. In any case, the Cr (VI) content should be kept so low that the Cr (VI) content on the passivated metal does not exceed 1 mg / m ² .

The preparation used for passivation preferably does not comprise Cr (VI) and particularly preferably no chromium compounds, and no other method step consciously uses chromium compounds, no matter what oxidation state. But even in this case, indirect and intrinsically unintentional small amounts of chromium can be introduced into the process. Namely, if zinc or aluminum alloys comprising chromium as an alloying component or zinc-plated steel in which the iron is alloyed with chromium are used in the method of the present invention, it is always within the range of possible to have small amounts of chromium in the metal to be treated can be solved by the preparation used for the process and accordingly can inadvertently get into the preparation itself. Even when using such metals and the resulting consequences, the process should be regarded as "essentially chromium-free".

The metallic surfaces which are passivated by means of the method according to the invention are surfaces of Zn, Zn alloys, Al or Al alloys. These may be the surfaces of bodies or workpieces made entirely of said metals or alloys. However, they may also be the surfaces of Zn, Zn alloy, Al or Al alloy coated bodies, which bodies may be made of other materials such as other metals, alloys, polymers or composites. In particular, it may be the surface of galvanized iron or steel. In a particular embodiment of the method is the surface of a strip metal, in particular electrolytically galvanized or hot-dip galvanized steel.

Zn or Al alloys are known to those skilled in the art. Depending on the desired application, the skilled person will select the type and amount of alloying components. Typical components of zinc alloys include in particular Al, Pb, Si, Mg, Sn, Cu or Cd. Typical constituents of aluminum alloys include in particular Mg, Mn, Si, Zn, Cr, Zr, Cu or Ti. It may also be Al / Zn alloys in which Al and Zn are present in approximately the same amount. Steel coated with such alloys is commercially available.

The preparation (Z) used for passivation comprises at least one water-soluble, uncrosslinked polymer or copolymer (A) which comprises at least 50% by weight of (meth) acrylic acid units (a1). The COOH groups may also be wholly or partially present as salts, for example as ammonium or Na salts.

The term water-soluble in the sense of this invention is intended to mean that the polymer or copolymers (A) used should be homogeneously water-soluble. Aqueous dispersions of crosslinked polymer particles of water-insoluble polymers are outside the scope of this invention.

Preferably, the (co) polymers used should be completely miscible with water, even if this is not absolutely necessary in every case. But they must be water-soluble at least to such an extent that the passivation by means of the method according to the invention is possible. As a rule, the (co) polymers used should have a solubility of at least 50 g / l, preferably 100 g / l and particularly preferably at least 200 g / l.

It is known to the person skilled in the art of water-soluble polymers that the solubility of COOH-group-containing polymers in water can be dependent on the pH. As a reference point, therefore, each of the desired for the particular application pH should be selected. A (co) polymer, which in a certain pH has insufficient solubility for its intended use, may have sufficient solubility at another pH.

The polymer or copolymer (A) may be pure polyacrylic acid or polymethacrylic acid.

However, (A) is preferably a copolymer which comprises from 50 to 99% by weight of (meth) acrylic acid units (Aa) and additionally from 1 to 50% by weight of at least one further ethylenically unsaturated comonomer other than (meth) acrylic acid ,

Preferably, the copolymer comprises 60 to 95% by weight, more preferably 65 to
90% by weight and most preferably 70 to 85% by weight
(Meth) acrylic acid units (Aa).

The comonomers must meet a number of requirements: they must be copolymerizable with (meth) acrylic acid and optionally other comonomers. Furthermore, the copolymer (A) must be water-soluble.

The at least one comonomer is in particular at least one comonomer (Ab) different from (meth) acrylic acid, which has an ethylenically unsaturated group and an acidic group. These may likewise be carboxylate groups, but also other acidic groups such as, for example, phosphoric acid, phosphonic acid or sulfonic acid groups. The comonomers may each have only the same or different acidic groups. Of course, several different comonomers (Ab) can be used with acidic groups.

Examples of comonomers (Ab) include COOH-containing acids of the general formula RHC = CH- (CH ₂ ) _n -COOH with n = 1 to 8, and R = H or C ₁ to C ₃ such as vinylacetic acid, crotonic acid or isocrotonic acid , two COOH-containing unsaturated acids such as maleic acid or fumaric acid, phosphonic acid-containing acids such as vinylphosphonic acid, allyphosphonic acid or 3-butenylphosphonic acids such as Phosphoric acid monovinyl ester, Phosphorsäuremonoallylester, phosphoric acid (mono-3-butenyl) ester or (meth) acrylic acid (phosphonoxyethyl ) esters or sulfonic acid-containing acids such as styrene sulfonic acid.

Examples of particularly suitable comonomers (Ab) include maleic acid, fumaric acid and vinylphosphonic acid.

Preference is given to 2 to 50 and more preferably 5 to 40% by weight of further comonomers (Ab).

The copolymer (A) may further comprise one or more comonomers (Ac) which comprise an ethylenically unsaturated group but not an acidic group. Examples of such monomers include olefins such as ethylene, propylene or styrene, esters of vinyl alcohol and monocarboxylic acids, especially such as vinyl acetate or vinyl propionate, and further especially (meth) acrylates having a wide variety of alcohol radicals such as methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl ( meth) acrylate or 2-ethylhexyl (meth) acrylate. It may also be OH-containing monomers, such as p-vinylphenol or in particular ethoxylated or propoxylated (meth) acrylic acid.

The comonomers (Ac) are used to fine-tune the properties. If present, their amount is determined depending on the desired properties of the polymers, for example their solubility. However, the amount should as a rule not exceed 30% by weight, preferably 20% by weight, particularly preferably 10% by weight and very particularly preferably 5% by weight.

The copolymers (A) can be prepared by methods known to those skilled in the art. The polymers and / or copolymers are preferably prepared by free-radical copolymerization of the abovementioned components (Aa) and, if appropriate, (Ab) and / or (Ac). Monomers having more than one ethylenically unsaturated group, which have a corresponding crosslinking effect, can be used in special cases for the fine control of the properties. However, they should at most be used in a very small amount, so that the polymer remains essentially uncrosslinked. The amount of a crosslinking monomer should as a rule not exceed 1% by weight, preferably 0.5% by weight, and preferably none is used at all.

The preparation of the polymers can also be carried out by using in the case of the acidic monomers for the polymerization not the free acids, but in the form of their salts, esters, anhydrides or other hydrolyzable derivatives. Free acid groups can then be obtained therefrom in a separate step by hydrolysis, if appropriate using suitable bases. In particular, maleic acid is usually polymerized in the form of maleic anhydride and hydrolyzed only after the polymerization, or possibly even in the preparation.

The average molecular weight of the (co) polymers used is not limited in principle, as long as the (co) polymers are still sufficiently soluble in water. It is determined by the person skilled in the art according to the desired application. By choosing a specific molecular weight, the person skilled in the art can, for example, influence the viscosity of the preparation and tailor it for the desired purpose. In general, the weight average M _{w of} the polymers is from 500 to 2,000,000 g / mol, preferably from 1,000 to 1,000,000, more preferably from 2,000 to 500,000 g / mol and very particularly preferably from 3,000 to 300,000 g / mol.

The copolymer (A) is particularly preferably one composed of (meth) acrylic acid and maleic anhydride, in particular from 70 to 80% by weight of (meth) acrylic acid and from 20 to 30% by weight of maleic anhydride.

In addition to (meth) acrylic acid and maleic anhydride, vinylphosphonic acid may furthermore preferably be used as further comonomer in amounts of 1 to 30% by weight, preferably 1 to 20% by weight and more preferably 1 to 10% by weight. A preferred copolymer may, for example, be composed of 70 to 80% by weight of (meth) acrylic acid, 15 to 25% by weight of maleic anhydride and 1 to 10% by weight of vinylphosphonic acid.

The maleic anhydride units are hydrolyzed directly at the beginning, in parallel or following the polymerization to maleic acid units, preferably with a base such as triethanolamine.

As component (b), the preparation (Z) used for the process according to the invention preferably comprises only water or an aqueous solvent mixture containing at least 50% by weight of water. If an aqueous mixture is used, the mixture preferably comprises at least 65% by weight, more preferably at least 80% by weight and most preferably at least 95% by weight of water. The data refer to the total amount of all solvents. Other components of a mixture are water-miscible solvents. Examples include monoalcohols such as methanol, ethanol or propanol, higher alcohols such as ethylene glycol or polyether polyols and ether alcohols such as butyl glycol or methoxypropanol.

Preferably, only water is used as solvent.

The concentration of the polymers or copolymers (A) in the formulation will be determined by one skilled in the art according to the desired application. For example, the thickness of the passivation layer depends on the chosen process technology, but also, for example, on the viscosity of the composition used for the passivation. In general, a concentration of 0.01 g / l has proven to 500 g / l, preferably 0.1 g / l to 200 g / l, and more preferably 0.5 g / l to 5 g / l. The concentrations given refer to the ready-to-use preparation. As a rule, it is possible first to prepare a concentrate which is first diluted to the desired concentration with water or optionally other solvent mixtures on site.

The preparation (Z) used according to the invention is acidic. It generally has a pH of 1 to 6, wherein depending on the substrate and method of application and duration of exposure of the preparation (Z) on the surface tighter pH ranges may be selected. For example, the pH for treating aluminum surfaces is preferably set in the range of 2 to 4, and in the case of treating zinc or galvanized steel, preferably in the range of 2 to 5.

The pH of the preparation can be controlled on the one hand by the nature and concentration of the COOH-containing polymers or copolymers and thus results automatically.

However, the preparation may optionally also comprise at least one inorganic or organic acid or mixtures thereof. Examples of suitable acids include phosphorus, sulfur or nitrogen-containing acids such as phosphoric acid, phosphonic acid, sulfuric acid, sulfonic acids such as methanesulfonic acid, sulfamic acid, p-toluenesulfonic acid, m-nitrobenzenesulfonic acid and derivatives thereof, nitric acid, hydrofluoric acid, hydrochloric acid, boric acid, formic acid, oxalic acid or acetic acid. The acid is preferably selected from the group consisting of HNO ₃ , H ₂ SO ₄ , H ₃ PO ₄ , formic acid or acetic acid. Particularly preferred are H ₃ PO ₄ and / or HNO ₃ . Of course, mixtures of different acids can be used.

The type and concentration of the acid in the preparation (Z) is determined by the skilled person according to the desired application and pH. In general, a concentration of 0.01 g / l to 30 g / l, preferably 0.05 g / l to 3 g / l, and more preferably 0.1 g / l to 5 g / l has proven.

According to the invention, at least one water-soluble crosslinker is furthermore used for the process, where the crosslinker comprises at least 2 crosslinking groups selected from the group of azirane, oxirane or thiirane groups. As a rule, the crosslinkers used have only one type of crosslinking groups, even if deviations from this rule are to be possible in special cases. Likewise, it is preferred when using a plurality of different crosslinkers, if they have only one type of crosslinking groups.

Preferably, the crosslinkers used should be completely miscible with water, even if this is not absolutely necessary in every case. But they must be water-soluble at least to such an extent that the passivation by means of the method according to the invention is possible. The crosslinkers used have a solubility in water of at least 10 g / l, preferably 30 g / l and particularly preferably at least 60 g / l.

The number average molecular weight M _{n of} the crosslinker is from 112 to about 5000 g / mol, preferably from 150 to 2500 g / mol and more preferably from 200 to 2000 g / mol.

The at least two crosslinking groups are connected to one another by means of a linking group X comprising at least 2 C atoms. In the case of oxirane and thirane groups, it is naturally possible to link only in the 2 or 3 position of the three-membered ring. For azirane groups, the 1-position is also an option. This is also the preferred position. Oxirane or azirane crosslinkers are preferred.

The linking group X may be a straight-chain, branched or cyclic aliphatic, aromatic or araliphatic group, which may also have additional heteroatoms or substituents. The linking group is preferably a straight-chain or branched aliphatic group in which non-adjacent carbon atoms may also be replaced by O atoms.

The crosslinkers comprise at least 2 crosslinking groups. The number of crosslinking groups is not limited to the top. However, a number of from 2 to 20, preferably from 2 to 10 and particularly preferably from 3 to 6 crosslinking groups has proven useful.

wobei es sich bei m um eine natürliche Zahl ≥ 2 handelt. Bevorzugt handelt es sich bei m um eine natürliche Zahl von 2 bis 6. Bei R² handelt es sich um H und/oder eine Methylgruppe. Bevorzugt umfasst ein Vernetzermolekül nur die gleichen Reste R² an den vernetzenden Gruppen und besonders bevorzugt handelt es sich bei R² um ein H-Atom.In particular, proven for carrying out the present invention, at least two azirane-containing crosslinkers of the general formula (I)

where m is a natural number ≥ 2. Preferably, m is a natural number from 2 to 6. R ² is H and / or a methyl group. Preferably, a cross-linker molecule comprises only the same radicals R ² in the crosslinking groups, and most preferably, R ² is a hydrogen atom.

angebunden sind. Die Aziran-Gruppen sind also jeweils über verknüpfende Gruppen mit dem Rest R¹O_m- verbunden.The radical R ¹ O _m - is an m-valent, aliphatic alkoxy radical. The remainder has at least m O atoms to which m radicals of the general formula (Ia)

are connected. The azirane groups are thus linked via linking groups with the radical R ¹ O _m -.

The aliphatic alkoxy radicals R ¹ O _m - may have further O atoms or other heteroatoms such as, for example, N in the radical R ¹ . They are derived from the corresponding aliphatic alcohols R ¹ (OH) _m , where m '≥ m.

Examples of suitable alcohols include glycol, propanediol, butanediol, butenediol, butynediol, pentanediol, hexanediol, diglycol, triglycol, oligo- or polyethylene glycol, glycerol, polypropylene glycol, neopentyl glycol, polyglycerol, trimethylolmethane, trimethylolethane, trimethylolpropane, 1,2,4-butanetriol, Tris (hydroxymethyl) amine, tris (hydroxyethyl) amine, tris (hydroxypropyl) amine, pentaerythritol, bis (trimethylolpropane) or sugars, such as glucose or sorbitol. The alcohols can also be reacted with ethylene oxide, propylene oxide or butylene oxide to di- or higher functional polyetherols. Preferably, only ethoxylated products are used. The alcohols can also be oligomers or polymers of suitable molecular weight which comprise vinyl alcohol units, for example polyvinyl alcohol or polyvinyl alcohol copolymers.

Preferred for carrying out this invention are glycol, butanediol, glycerol, trimethylolethane, trimethylolpropane, 1,2,4-butanetriol, pentaerythritol, and their polyetherols based on ethylene oxide, particularly preferred is trimethylolpropane.

bewährt, wobei es sich bei m um eine natürliche Zahl ≥ 2 handelt. Bevorzugt handelt es sich bei m um eine natürliche Zahl von 2 bis 6.To prepare the crosslinkers of the general formula (I), it is possible first to react an m'-valent alcohol of the general formula R ¹ (OH) _m 'with (meth) acrylic acid or a suitable (meth) acrylic acid derivative to give a (meth) acrylic acid ester. Not all OH groups of the alcohol have to be reacted as long as at least 2 are reacted. In particular, (meth) acrylic acid anhydride is suitable for carrying out this reaction. The resulting ester is reacted in a second reaction step with azirane or 2-methylazirane, wherein the azirane is added by means of a Michael addition to the double bond of the (meth) acrylic acid unit. Azirane groups comprising crosslinkers of formula (I) are also commercially available, for example as Corial® hardener (BASF AG) In a further embodiment of the invention, at least two oxirane-containing crosslinkers of the general formula (II)

proven, where m is a natural number ≥ 2. Preferably, m is a natural number of 2 to 6.

The abbreviation R ¹ O _m - has the meaning given above. Preferred radicals in the crosslinkers (II) are derived from glycerol, oligoglycerols, in particular di- or triglycerol, glycol or polyethylene glycols of the general formula HO- (CH ₂ -CH ₂ -O) _n -H, where n is preferably from 2 to 25 stands.

To prepare the crosslinkers of the formula (II), a polyhydric alcohol of the general formula R ¹ (OH) _{m '} can be reacted with glycidyl chloride. Not all OH groups of the alcohol have to be reacted as long as at least 2 are reacted. Crosslinkers of the formula (II) comprising various oxirane groups are commercially available, for example under the trade name Denacol® (Nagase Chemicals Ltd.).

The person skilled in the art makes a suitable choice among the crosslinkers which are possible in principle, depending on the desired passivation conditions and the desired properties of the passivation layer.

The water-soluble crosslinkers used according to the invention can be dissolved in the preparation (Z) so that the treatment of the metallic surface with the crosslinker and the treatment with the preparation take place simultaneously.

However, it is also possible to treat the surface with the crosslinker in a separate step before and / or after the treatment with the preparation. The latter is particularly recommendable if the crosslinker is not completely inert in the chosen preparation and the selected passivation conditions, but reacts with the components of the preparation. Adverse reactions are also advantageously avoided by mixing the crosslinker only immediately before use in the preparation.

The ratio of the crosslinker to the polymer is determined by the person skilled in the art according to the desired properties. As a rule, a weight ratio of polymer to crosslinker of 0.05: 1 to 50: 1, preferably 0.1 to 20: 1 and particularly preferably 0.5: 1 to 10: 1, has proven useful.

The preparation may optionally further comprise other components via said components.

The optionally present components may be, for example, transition metal ions and compounds, for example Ce, Ni, Co, V, Fe, Zn, Zr, Ca, Mn, Mo, W, Ti, Zr, Hf, Bi, Cr and /. or the lanthanides act. If Cr is present, the quantities defined above should not be exceeded. Preferably, no Cr (VI) compounds are used, more preferably no chromium compounds at all. They may also be compounds of main group elements, such as Si and / or Al. The compounds can be used for example in the form of the respective aqua complexes. However, they can also be complexes with other ligands, such as, for example, fluoride complexes of Ti (IV), Zr (IV) or Si (IV) or oxometalates such as MoO ₄ ^2- or WO ₄ ^2- . Furthermore, it is also possible to use complexes with typical chelating ligands, such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), hydroxyethylethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA) or methylglycinediacetic acid (MGDA).

Other optional components include surface-active compounds, corrosion inhibitors or typical electroplating aids.

The person skilled in the art will make an appropriate selection of the optionally possible optional components and their quantities depending on the desired application.

In the method according to the invention for passivating metallic surfaces, the surface of the metal is treated with the preparation (Z) and with the crosslinker, for example by spraying, dipping or rolling. After a dipping process, you can drain the workpiece to remove excess treatment solution; in the case of metal sheets, metal foils or the like, however, excess treatment solution can also be squeezed off or doctored off, for example. In the treatment, at least parts of the polymer used as well as other components of the preparation are chemisorbed by the surface of the metal, so that a firm bond between the surface and the component comes about. Treatment with the preparation is usually carried out at room temperature without that higher temperatures should be excluded in principle.

If the crosslinker is not contained in the preparation, the crosslinker is preferably also dissolved in water, and applied to the metal surface by, for example, spraying, rolling or dipping before and / or after the treatment with the preparation without crosslinker. Of course, a part of the crosslinker may be included in the preparation, while a second part of the crosslinker is applied in a separate step.

The treatment may be a so-called "no-rinse" process, in which the treatment solution is dried directly in a drying oven immediately after application without rinsing.

However, it is also possible to rinse the surface after the treatment with a cleaning liquid, in particular with water, in order to remove residues of the preparation used according to the invention from the surface.

The crosslinking of the polymer by the crosslinker can also be carried out at room temperature. Preferably, however, the metal surface is heated after the treatment of the metal with the preparation and the crosslinker. A temperature of 30 ° C. to 120 ° C., preferably 40 ° C. to 100 ° C., and particularly preferably 50 ° C. to 80 ° C., has proven useful.

The treatment of the metal surface with the preparation and the crosslinker may be carried out batchwise or preferably continuously. A continuous process is particularly suitable for treating strip metals. The metal strip is driven by a pan or a spray device with the preparation and optionally a pan or spray device for the crosslinker and optionally by other pre- or post-treatment stations.

The duration of treatment will be determined by the skilled person according to the desired properties of the layer, the composition used for the treatment and the technical conditions. It can be significantly less than a second or several minutes. In the continuous process, it has proven particularly useful to contact the surface with the preparation for a period of 1 to 60 seconds.

Whether the crosslinker is added to the preparation or the metal surface treated with the crosslinker in a separate step is decided by the skilled person depending on the desired result and the conditions. The use of a preparation which already contains the crosslinker is easier and cheaper to carry out, because a separate second process step is not required.

The treatment with the preparation and with the crosslinker in two (or three) separate process steps, on the other hand, has the advantage that it provides more process-technological degrees of freedom that can be used for special effects.

As a rule, the preparation containing the crosslinker can not be heated to elevated temperatures for a relatively long time, since otherwise at least parts of the crosslinker are prematurely and undesirably mixed with the polymer, other constituents of the polymer Preparation or react with yourself. Such unwanted side reactions may degrade passivation layer properties and, in the worst case, even completely unusable results. The treatment in this case must therefore usually take place essentially at room temperature.

If the treatment with the crosslinker is carried out in a separate step, the treatment with the preparation can be carried out at significantly higher temperatures, for example at 50 to 80 ° C., without fear of undesired reactions of the crosslinker. As a result, the formation of the passivation layer can be accelerated and / or other properties of the passivation layer, such as, for example, its thickness, can be influenced. The treatment with the crosslinker is then carried out in a separate step, for example with a solution of the crosslinker at room temperature. It can be done afterwards, but also before the treatment with the preparation.

The process according to the invention may optionally also comprise one or more pretreatment steps. For example, the metallic surface can be cleaned prior to passivation with the preparation used according to the invention, e.g. to remove fats or oils. Furthermore, it can also be pickled prior to passivation to remove oxide scale, scale, temporary corrosion protection and the like. Furthermore, the surface must also be optionally rinsed with water after and between such pretreatment steps in order to remove the residues of rinsing solutions or pickling solutions.

By means of the method according to the invention, a passivation layer on a metallic surface of Zn, Zn alloys, Al or Al alloys is obtainable. The exact structure and composition of the passivation layer is unknown to us. However, in addition to the customary amorphous oxides of aluminum or zinc and, if appropriate, further metals, it also comprises the reaction products of the polymer and of the crosslinker and optionally further components of the layer. The composition of the passivation layer is not homogeneous, but the components appear to have concentration gradients.

The thickness of the passivation layer is adjusted by the person skilled in the art according to the desired properties of the layer. As a rule, the thickness is 0.01 to 3 μm, preferably 0.1 to 2.5 μm, and particularly preferably 1 to 2 μm. The thickness can be influenced, for example, by the type and amount of the applied components as well as the exposure time. Furthermore, it can be influenced by process parameters, for example by doctoring or rolling to over-applied treatment solution.

The thickness of the layer is determined by differential weighing before and after the action of the composition used according to the invention on the metal surface, assuming that the layer has a specific density of 1 kg / l. In the following, "layer thickness" is always understood to mean a size determined in this way, regardless of which specific density the layer actually has. These thin layers are sufficient to achieve excellent corrosion protection. Such thin layers ensure the dimensional accuracy of the passivated workpieces.

A further subject of the present application is a metallic surface which comprises the passivation layer according to the invention. The passivation layer is applied directly to the actual metal surface. In a preferred embodiment, strip metal is made of steel, which comprises a coating of Zn or a Zn alloy, and on which a passivation layer according to the invention is applied.

The metallic surface with passivation layer can be overcoated in a manner known in principle with one or more color or effect paint layers. Typical lacquers, their composition and typical layer sequences in the case of several lacquer coats are known in principle to the person skilled in the art.

The use of a water-soluble crosslinker according to the invention makes it possible to markedly increase the effectiveness of the passivation layer over layers without crosslinker.

The following examples are intended to illustrate the invention in more detail:

General experimental description

For the examples and comparative examples test plates made of galvanized steel (20 microns one-sided zinc coating) were used

• Unpassivierte Stahlbleche wurden 10 s in eine Reinigungslösung aus 0,5% HCl und
• 0,1 % eines Alkylphenolethoxylats mit 10 Ethylenoxid-Einheiten getaucht, sofort mit Wasser abgespült und anschließend mit Stickstoff getrocknet.

In the examples the following sheet pretreatment was chosen:

• Unpassivated steel sheets were placed in a cleaning solution of 0.5% HCl and 10 s for 10 s
• 0.1% of an alkylphenol ethoxylate dipped with 10 ethylene oxide units, rinsed immediately with water and then dried with nitrogen.

Preparation of the compositions for passivation:

In each case 5% aqueous solutions of the polymer used in each case were homogenized and filled in a dipping bath. The solutions also contained 0.1% by weight of HNO ₃ or H ₃ PO ₄ . The pre-cleaned sheets were immersed for 10 seconds and at Room temperature dried. Finally, the edges of the passivated sheets were taped to eliminate edge effects.

The sheets were passivated as described below.

The thickness of the passivation layer was determined by differential weighing before and after exposure of the composition used according to the invention to the metal surface and assuming that the layer has a specific gravity of 1 kg / l. In the following, "layer thickness" is always understood to mean a size determined in this way, regardless of which specific density the layer actually has.

• Bilden sich weiße Flecken von im Allgemeinen mehr als 1 mm Durchmesser (Zn-oder Al-Oxid, sogenannter Weißrost), so wird die Standzeit als die Zeit angegeben, nach der das Schadbild dem Bewertungsgrad 8 in DIN EN ISO 10289 vom April 2001, Anhang B, Seite 19, entspricht.
• Bilden sich schwarze Flecken von im Allgemeinen weniger als 1 mm Durchmesser bevor sich Weißrostflecken bilden, so wird die Standzeit als die Zeit angegeben, nach der das Schadbild dem Bewertungsgrad 8 in DIN EN ISO 10289 vom April 2001, Anhang A, Seite 9, entspricht.

The corrosion-inhibiting effect was determined by means of a salt spray test according to DIN 50021. Depending on which type of corrosion damage is observed, the service life in the corrosion test is defined differently.

• If white spots of generally more than 1 mm in diameter are formed (Zn or Al oxide, so-called white rust), the service life is given as the time after which the damage pattern corresponds to the evaluation level 8 in DIN EN ISO 10289 of April 2001, Appendix B, page 19.
• If black spots of generally less than 1 mm in diameter are formed before white rust spots form, the lifetime is reported as the time after which the damage pattern corresponds to the evaluation level 8 in DIN EN ISO 10289 of April 2001, Appendix A, page 9.

Example 1: Passivation layer with aziridine crosslinker (I) and acrylic acid copolymer

Dispense once for 10 s into a 5% strength by weight ethanolic solution of trimethylolpropane tris (beta-aziridino) propionate (solubility of the crosslinker in water 60 g / l). The layer thickness is 0.6 μm.

Subsequent dipping for 10 seconds at RT in a 5% aqueous solution of poly (acrylic acid-co-maleic acid) in 0.1% HNO ₃ with a weight-based monomer composition of 80:20 and adjusted with triethanolamine pH of 3 ; 5. The sheet after 5 minutes of drying / curing at room temperature shows no changes in color and metallic luster to the original sheet. The layer thickness is 1.8 μm (polymer + crosslinker together).

A salt spray test was performed until Grade 8 in a 5% salt spray atmosphere at 35 ° C. The residence time / life up to rating 8 was 50 h.
The results are summarized in Table 1.

Example 2: Passivation layer with aziridine crosslinker [I] and acrylic acid copolymer

Dispense once at RT for 10 sec into a 5% aqueous formulation of solution 1 (85 wt% trimethylolpropane tris (beta-aziridino) propionate, 7.5% diacetone alcohol and 2.5% triethylenediamine) and dry the plate at room temperature ,

Subsequent dipping in solution 2 (5% aqueous poly (acrylic acid-comaleic acid) solution as in Example 1). The sheet after 5 minutes of drying / curing at room temperature shows no changes in color and metallic luster to the original sheet. The layer thickness is 1.65 μm in total.

A salt spray test was performed as described above. The residence time was 50 h. The results are summarized in Table 1.

Example 3: Passivation layer with oxirane crosslinker [II] and acrylic acid copolymer

Single immersion for 10 seconds at RT in a 5% aqueous solution of a poly (acrylic acid-co-maleic acid) solution having a weight-based monomer composition of 80:20 and a pH adjusted to 3.5 with triethanolamine and the crosslinker glycerol diglycidyl ether (Denacol ® 313, solubility of the crosslinker in water 100 g / l) in 0.1% HNO ₃ . The weight ratio of polymer to crosslinker is 32:68.

The plate shows after 5 minutes of drying / curing at 80 ° C, no changes in color and metallic luster to the original sheet. The layer thickness is 1.4 μm.

A salt spray test was performed as described above. The residence time was 29 h. The results are summarized in Table 1.

Comparative Example 1 Passivation layer with acrylic acid copolymer

Discrete dipping for 10 sec. At 40 ° C in a 5% aqueous poly (acrylic acid-co-maleic acid) solution having a weight-based monomer composition of 80:20 and a pH of 3.5 adjusted with triethanolamine. After 5 minutes of drying / hardening at 70 ° C., the sheet shows no changes in color and metallic luster to the original sheet. The layer thickness is 1.1 μm.

Residence time up to grade 8 in a 5% salt spray atmosphere at 30 ° C is 21 h.

Comparative Examples 2 and 2a, respectively

Treatment of the metal only with HNO ₃ (Ex 2) or H ₃ PO ₄ (Ex. 2a)

Single immersion for 10 sec at RT in a 0.1% aqueous solution of phosphoric acid or nitric acid

The residence time until assessment 8 in a 5% salt spray atmosphere at 30 ° C. is <2 h in each case.

Comparative Example 3 Passivation layer with acrylic acid copolymer and bisphenol A diglycidyl ether

Single immersion for 10 sec at RT in a 5% strength by weight ethanolic solution of bisphenol A diglycidyl ether. The layer thickness is 1.6 μm.

Dispense once at 40 ° C for 10 sec. Into a 5% poly (acrylic acid-co-acrylic acid) aqueous solution having a weight average monomer composition of 80:20 and a triethanolamine pH of 3.5 in 0.1% HNO ₃ . The sheet shows after 5 minutes of drying / hardening at 70 ° C spotty and dark changes in color and metallic luster to the original sheet.

The total layer thickness (crosslinker + polymer together) is 2.2 μm.

Dwell time up to grade 8 in a 5% salt spray atmosphere at 30 ° C is 19 hours.

Comparative Example 4 Passivation layer of azirane crosslinker [I]

Dispense once for 10 sec into a 5 wt% ethanolic solution of trimethylolpropane tris (beta-aziridino) propionate. The layer thickness is 1.0 μm.

Dwell time up to grade 8 in a 5% salt spray atmosphere at 30 ° C is <2 h. Table 1: Results of the experiments and comparative experiments No. polymer crosslinkers Remarks Layer thickness [μm] Life in the salt spray test [h] up to the damage picture 8 Standardized service life (= service life / layer thickness) [h / μm] example 1 Acrylic acid / maleic acid copolymer Aziranvernetzer First treatment with crosslinker, then polymer 1.8 50 28 Example 2 Acrylic acid / maleic acid copolymer Aziranvernetzer First treatment with crosslinker, then polymer 1.65 50 30 Example 3 Acrylic acid / maleic acid copolymer Oxiranvernetzer Polymer and crosslinker at the same time 1.4 29 21 Comparative Example 1 Acrylic acid / maleic acid copolymer - no networking 1.1 21 19 Comparative Example 2 - - Only with 0.1% nitric acid - <2 0 Comparative Example 3 Acrylic acid / maleic acid copolymer Bisphenol A spotty, dark 2.2 19 8th Comparative Example 4 - Aziranvernetzer Only crosslinkers 1.0 <2 2

The present examples show that the use of crosslinkers can greatly improve the corrosion resistance of zinc surfaces by chemically stabilizing the passivating polyacrylate layer by reactive crosslinkers. For this purpose, highly reactive polyfunctional azirane or Oxiranvernetzer are suitable. Due to their reactivity, the azirane crosslinkers can be used at room temperature and are stronger in their action than the oxirane crosslinkers.

The crosslinker alone gives no effect, and the polymer alone shows a significantly worse effect than the combination of crosslinker and polymer.

With non-water-soluble bisphenol A-type oxirane crosslinkers, only an inhomogeneous layer is obtained. Despite having a significantly greater layer thickness, it even shows a deterioration in comparison to a test without the use of crosslinking agents.

Claims (24)

1. A substantially chromium-free process for passivating metallic surfaces of Zn, Zn alloys, Al or Al alloys by treating the surface with an acidic aqueous formulation of a polymer comprising -COOH groups and/or salts thereof, wherein the formulation (Z) used for the treatment at least comprises

   (a) at least one substantially noncrosslinked, water-soluble polymer or copolymer (A) comprising at least 50% by weight of (meth)acrylic acid units, and

   (b) water or an aqueous solvent mixture (B) comprising at least 50% by weight of water,

   and the surface is further treated with at least one water-soluble crosslinker, the crosslinker comprising at least 2 crosslinking groups selected from the group consisting of azirane, oxirane, and thiirane groups and joined to one another by means of a linking group (X) comprising at least 2 carbon atoms, the number-average molecular weight M_n of the crosslinker being from 112 to 5000 g/mol, the solubility of the crosslinker in water being at least 10 g/l, and the treatment with the crosslinker being carried out before, after or simultaneously with the treatment with the formulation (Z).
2. The process according to claim 1, wherein the treatment with the crosslinker and with the formulation (Z) is carried out simultaneously and the crosslinker is present in the formulation (Z).
3. The process according to claim 1 or 2, wherein (Z) further comprises an organic or inorganic acid.
4. The process according to claim 3, wherein the acid is H₃PO₄ and/or HNO₃.
5. The process according to any one of claims 1 to 4, wherein the crosslinker is a crosslinker of the general formula (I)

   

   which contains at least two azirane groups and where m is a natural number ≥ 2, R¹O_m- is an m-valent, aliphatic alkoxy radical, and R² is H or methyl.
6. The process according to any one of claims 1 to 4, wherein the crosslinker is a crosslinker of the general formula (II)

   

   which contains at least two oxirane groups and where m is a natural number ≥ 2, and R¹O_m- is an m-valent, aliphatic alkoxy radical.
7. The process according to claim 5 or 6, wherein m is a natural number from 2 to 6.
8. The process according to any one of claims 1 to 7, wherein the water-soluble polymer (P) comprises (meth)acrylic acid.
9. The process according to any one of claims 1 to 7, wherein the water-soluble polymer (P) is a copolymer which in addition to the (meth)acrylic acid units further comprises at least one comonomer which comprises acidic groups but is other than (meth)acrylic acid.
10. The process according to any one of claims 1 to 9, wherein the weight ratio of polymer to crosslinker is from 0.5 : 1 to 50 : 1.
11. The process according to any one of claims 1 to 10, wherein the solvent is water.
12. The process according to any one of claims 1 to 11, wherein subsequently the metal surface is heated after the treatment.
13. The process according to any one of claims 1 to 12, wherein the treatment takes place by means of rolling, spraying or dipping methods.
14. The process according to any one of claims 1 to 13, wherein the metal surface is the surface of a strip metal.
15. The process according to claim 14, wherein the strip metal is electrolytically galvanized or hot-dip galvanized steel.
16. The process according to claim 14 or 15, wherein the treatment is carried out by means of a continuous process.
17. The process according to any one of claims 14 to 16, wherein the surface is contacted with the formulation for a time of from 1 to 60 s.
18. A passivating layer on a metallic surface of Zn, Zn alloys, Al or Al alloys, obtainable by a process according to any one of claims 1 to 17.
19. The passivating layer according to claim 18, whose thickness is from 0.01 to 3 µm.
20. A metallic surface comprising a passivating layer according to claim 18 or 19.
21. The metallic surface according to claim 20, wherein atop the passivating layer there are one or more paint layers.
22. A strip metal of steel comprising a coating of Zn or a Zn alloy which has a surface according to claim 20 or 21.
23. An acidic, substantially chromium-free formulation for passivating metallic surfaces of Zn, Zn alloys, Al or Al alloys, comprising at least

    (a) at least one substantially noncrosslinked, water-soluble polymer or copolymer (A) which comprises at least 50% by weight of (meth)acrylic acid units,

    (b) water or an aqueous solvent mixture (B) comprising at least 50% by weight of water, and

    (c) at least one water-soluble crosslinker of the general formula

    

    or

    

    where m is a natural number from 2 to 6, R¹O_m- is an m-valent alkoxy radical, and R² is H or methyl, and the number-average molecular weight M_n of the crosslinker is from 112 to 5000 g/mol, and the solubility of the crosslinker in water is at least 10 g/l.
24. The formulation according to claim 23, further comprising H₃PO₄ and/or HNO₃.