EP3426822A1

EP3426822A1 - Fluoride-free zirconium-based metal pre-treatment for passivation

Info

Publication number: EP3426822A1
Application number: EP17701835.5A
Authority: EP
Inventors: Jörg Riesop; Volker GEICK
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2016-03-08
Filing date: 2017-01-23
Publication date: 2019-01-16
Anticipated expiration: 2037-01-23
Also published as: DE102016203771A1; CN108699699A; CA3015541A1; WO2017153075A1; KR20180118680A; ES2831777T3; CN108699699B; US11142827B2; BR112018016295B1; JP2019513892A; AU2017229193A1; EP3426822B1; AU2017229193B2; JP7049259B2; BR112018016295A2; US20190010610A1

Abstract

The invention relates to a method for the anti-corrosion pre-treatment of metal substrates by using zirconium-based aqueous anti-corrosion agents. The anti-corrosion effect of the zirconium-based agent is based on the presence of polycyclic hydrocarbons that have at least one anellated benzene ring, each having at least two ring-substituted hydroxyl groups in ortho position to each other. The aqueous anti-corrosion agent can be substantially free both of passivating chromium-containing compounds and of fluoride-containing compounds that pickle the metal substrate. According to the invention, pre-treatment by drying (dry-in-place method) is especially advantageous. Accordingly, the method according to the invention is suitable in particular for the pre-treatment of metal strip, wherein excellent anti-corrosion results are achieved on surfaces of aluminum or steel. The invention further relates to a method for producing coated can lids from aluminum strip by using the previously mentioned zirconium-based anti-corrosion agent. A further aspect comprises an aqueous concentrate for providing the ready-to-use anti-corrosion agent.

Description

Fluoride-free zirconium-based metal pretreatment for passivation

The present invention relates to a process for the anticorrosive pretreatment of metal substrates using zirconium-based aqueous corrosion inhibitors. The anticorrosion effect of the zirconium-based agent is based on the presence of polycyclic hydrocarbons which have at least one fused benzene ring with at least two nucleus-substituted hydroxyl groups in ortho-position to each other. The aqueous anticorrosive agent may be essentially free of passivating chromium-containing compounds as well as fluoride-containing compounds which add to the metal substrate. According to the invention, the pretreatment by drying (dry-in-place method) is particularly advantageous. Accordingly, the inventive method is particularly suitable for the pretreatment of metal strip, with excellent

Corrosion protection results can be achieved on surfaces of aluminum or steel. The invention additionally includes a method for producing coated aluminum can lids using the aforementioned zirconium-based

Corrosion protection agent. In another aspect, an aqueous concentrate is included for providing the ready-to-use corrosion inhibitor.

The conversion treatment of metallic surfaces to provide a corrosion-protective coating based on aqueous compositions containing water-soluble compounds of zirconium is a technical field extensively described in the patent literature. To improve the property profile of such

Conversion treatments in terms of corrosion protection and providing adequate paint adhesion are known various variants of such a metal pretreatment, either aimed at the composition of the conversion effecting agents or resort to further wet chemical treatment steps in the immediate context of the conversion treatment.

In this context, various method variants for providing the passivating coating are known in principle, wherein the drying of the same after

Applying a defined wet film always allows a pretreatment in as few steps as possible and in this respect occupies a prominent position in procedural perspective.

Basically, the application of aqueous corrosion inhibitors by drying a wet film is fully established and implemented in practice. For this purpose, DE 199 33 186 A1 can be used, for example, to remove a roll application method which enables the application of a defined wet film of conventional aqueous corrosion inhibitors based on fluorocomplexes of the elements zirconium and / or titanium on flat products and their controlled drying. Nevertheless, the coatings differ by Drying a wet film can be obtained in your morphological and chemical

Texture clearly from the classical conversion layers, which are accessible by immersion or spray application after subsequent removal of adhering to the metal substrate wet film of the corrosion inhibitor. Usually, all active components of the anticorrosive agent, which do not change to gaseous state on drying, are deposited on the metal substrate during the drying process. Accordingly, this includes not only all nonvolatile compounds of the elements intended for the passive layer, for example oxides / hydroxides or phosphates of the zirconium element, but also all nonvolatile active components of the anticorrosive agent and intermediates of the same elements used in the case of water-soluble fluorocomplexes of the element zirconium

Active component of the anticorrosion agent has a significant fluoride content in the

cause dried coating. However, these not completely converted active components and intermediates, which have become part of the dried coating, are usually the cause of inadequate corrosion protection properties or the need for aftertreatment. In this connection, EP 1 455 002 A1 specifies, for example, that the proportion of fluorides in the passivating coating caused by wet-chemical conversion by means of water-soluble fluoro compounds of the element zirconium should not exceed a certain proportion and at the same time suggests drying as a suitable after-treatment at elevated temperatures Temperature and rinsing with an alkaline solution before, to bring about a significant reduction of the fluoride content.

Accordingly, there continues to be a need to provide a process, which is as efficient as possible in terms of the number of necessary process steps, for the corrosion-protective pretreatment of metallic substrates, in which the passivating effect of compounds of the element zirconium is used. It is of particular importance to provide such an anticorrosion agent that excellent results are achieved already by applying and drying ("dry-in-place" method) .Excellent results are achieved when the application in the dry-in-place process results in coatings, in addition to their temporary corrosion-protecting effect in conjunction with subsequently applied primer coatings based on film-forming organic resins, provide excellent protection against corrosive softening In the present case, it is desirable to be able to cope with beverage cans, which is advantageously to be applied in one of these processes

Corrosion inhibitors also largely free of environmentally harmful fluoride-releasing compounds.

This range of tasks is solved by a process for corrosion protection

Pretreatment of a metallic substrate, wherein the surface of the metallic substrate is contacted with an aqueous corrosion inhibitor containing at least one water-soluble compound (A) of the element zirconium, which additionally comprises at least one polycyclic hydrocarbon (B) having at least one fused benzene ring each having at least two nucleus-substituted hydroxyl groups in the ortho position has to each other.

A compound (A) of the element zirconium is water-soluble in the context of the present invention, when the same at 20 ° C in deionized water, which has a specific conductivity of less than Ι μβαττ ¹ , a solubility of at least 0.1 g of the compound as to zirconium per kilogram of the aqueous solution prepared thereby.

In the method according to the invention it is ensured that, as a result of a pickling attack on the metallic substrate, a passivation of the metallic substrate is mediated by a

Surface coverage based on sparingly soluble compounds of the element zirconium and the polycyclic hydrocarbon occurs. In addition, metallic substrates pretreated according to the invention, which thus have a corresponding surface coverage, are ideally suited for imparting an excellent lacquer adhesion to subsequent primers comprising film-forming organic resins. For this purpose, the aqueous corrosion-protection agent can additionally contain organic polymers, without the passivation being adversely affected.

For a good passivation, to which the presence of the paint adhesion improving organic polymers does not adversely affect, it is particularly advantageous if the polycyclic hydrocarbon (B) has a low solubility in water, so that for a sufficient surface coverage in each application method necessary dissolved amount of polycyclic hydrocarbon (B) ideally just in the aqueous

Corrosion inhibitor dissolved present. In this connection are inventive

Preferred method in which the polycyclic hydrocarbon (B) at 20 ° C in deionized water having a conductivity of less than 1 μ8ϋητ has a solubility of less than 5 g, more preferably less than 1 g per kilogram of aqueous solution prepared thereby , Such a low solubility of the polycyclic hydrocarbon (B) is particularly advantageous when applying the anticorrosion agent in the drying process (so-called "dry-in-place process"), in which even small amounts of

Active components of the corrosion inhibitor for a passivating acting

Surface coverage of the metallic substrate to be protected may be sufficient. The term of solubility in water with respect to the compound (B) is understood to mean that above the mentioned solubility limits at a shear rate of 100 s ^~ dispersions or emulsions having an average particle diameter (D50 value) calculated from cumulative particle diameter distribution curves determined by means of dynamic light scattering methods more than 50 nm result.

In a preferred embodiment of the process according to the invention, the polycyclic hydrocarbon (B) contains at least two fused benzene rings each having at least two nucleus-substituted hydroxyl groups in ortho-position to each other, wherein the benzene rings each bridged by Anellierung to an acyclic hydrocarbon system, wherein the acyclic hydrocarbon system is preferably at least a Having oxo group or hydroxyl group. Such polycyclic hydrocarbons (B) are familiar to the person skilled in the art, for example in the form of hematoxylin and its oxidation product hematin as well as in the form of alizarin.

A particularly homogeneous surface coverage based on the element zirconium and thus also passivation succeeds when the pretreatment according to the invention takes place in the presence of polycyclic hydrocarbons (B) which build up on the anthraquinone skeleton. In the following, preference is given to those polycyclic hydrocarbons (B) in processes according to the invention which are selected from the group of anthraquinones which are nuclear-substituted with at least two hydroxyl groups ortho to one another, more preferably selected from the group consisting of 1, 2-dihydroxyanthraquinone, 3 , 4-Dihydroxyanthraquinone, 1, 2,3-trihydroxyanthraquinone, 1, 2,4-trihydroxyanthraquinone, 1, 2,3-trihydroxyanthraquinone, 1, 2,5-trihydroxyanthraquinone, 1, 2,6-trihydroxyanthraquinone, 1, 2,7 Trihydroxyanthraquinone, 1, 2,8-trihydroxyanthraquinone, 1, 2,3-trihydroxyanthraquinone, 1, 3,4-trihydroxyanthraquinone, 1, 4,5-trihydroxyanthraquinone, 1, 6,7-trihydroxyanthraquinone, 1, 2,5,8 -Tetrahydroxyanthraquinone, 1, 2,5,8-tetrahydroxyanthraquinone 1, 4,5,8-tetrahydroxyanthraquinone, 1, 2,3,4-tetrahydroxyanthraquinone, particularly preferred is the polycyclic hydrocarbon (B) selected from 1, 2-hydroxyanthraquinone.

Furthermore, the ratio of water-soluble compounds (A) of the element zirconium to polycyclic hydrocarbons (B) should be within a certain range for optimum passivation of the surfaces of the metallic substrates pretreated in the process according to the invention. Preferably, the weight ratio of water-soluble compounds (A) of the zirconium element to polycyclic element is zirconium

Hydrocarbons (B) in the corrosion inhibitor of the inventive method is less than 0.2, more preferably less than 0, 1, but preferably greater than 0.02.

Preferred amounts of the polycyclic hydrocarbons (B) in the corrosion inhibitor of the process according to the invention are in the range of 5-250 mg / kg.

The anticorrosive agent used in the method of the present invention is preferably made acidic for increased solubility of the water-soluble compounds (A) of the element zirconium and an effect to attract the metal substrate. In a preferred

Embodiment of the method according to the invention, the pH of the corrosion inhibitor is less than 2.0, more preferably less than 1, 6, but preferably greater than 0.5, more preferably greater than 1, 0.

The inventive method is characterized by the fact that a high pickling removal thus a high metal dissolution rate during the contacting with the corrosion inhibitor for a sufficient surface passivation is not necessary. Consequently, in particularly advantageous embodiments of the invention, the anticorrosion agent can be formulated to a large extent free of environmentally harmful fluorides or fluoride-releasing compounds, which are usually used to increase the pickling rate, in particular

Aluminum substrates are used.

Accordingly, processes according to the invention are preferred for which the molar ratio of zirconium to the total fluoride content in the homogeneous aqueous phase of the

Corrosion inhibitor greater than 1, preferably greater than 2, more preferably greater than 4. The total fluoride content is in a TISAB buffered aliquot part of the

Anticorrosion agent with a fluoride-sensitive electrode determined at 20 ° C (TISAB: "Total Lonic Strength Adjustment Buffer"), wherein the volume-related mixing ratio of buffer to aliquot of the anticorrosive agent is 1: 1. The TISAB buffer is prepared by dissolution of 58 g NaCl, 1 g of sodium citrate and 50 ml of glacial acetic acid in 500 ml of deionized water (K <1 μ8ϋητ) and setting a pH of 5.3 using 5 N NaOH and filling to a total volume of 1000 ml again with deionized water (κ <Ι μβαττ ¹ ).

It is further preferred in this context according to the invention that the source of the water-soluble compound (A) of zirconium is not also a source of fluoride ions and is preferably selected from zirconyl nitrate, zirconium acetate and / or

Ammonium zirconium carbonate, more preferably zirconyl nitrate.

The preferred amount of the water-soluble compound (A) in the anticorrosion agent of the method according to the invention is at least 40 mg / kg, more preferably at least 200 mg / kg, in particular at least 400 mg / kg, but preferably not more than 4000 mg / kg in each case based on the amount of the element zirconium.

In a particularly preferred embodiment of the process according to the invention, the total fluoride content in the aqueous phase of the anticorrosive agent is less than 50 mg / kg, preferably less than 10 mg / kg, more preferably less than 1 mg / kg, in each case based on the corrosion inhibitor.

Another ecological advantage of the present invention is also that the corrosion inhibitor need not contain sparingly soluble salts forming anions, such as phosphates, to form a passivating coating. In a preferred

Embodiment of the method according to the invention are therefore in the corrosion inhibitor less than 0.2 wt .-%, more preferably less than 0, 1 wt .-%, of dissolved phosphates calculated as PÜ4 included. The method according to the invention is outstandingly suitable for applying a paint adhesion base to metallic substrates, in particular by drying a wet film of the film

Corrosion inhibitor to provide. This suitability implies that the presence of paint adhesion improving organic polymers in the aqueous corrosion inhibitor does not adversely affect the passivation. In a preferred embodiment of the

The process according to the invention, in which organic polymers are used for further improving the paint adhesion, are therefore at least 0.1% by weight, more preferably at least 0.2% by weight, of organic compounds (C), in each case based on the aqueous corrosion inhibitor Contain corrosion inhibitors having a molecular weight above 5,000 g / mol. In the present case, the molar mass can be determined directly in the anticorrosive agent at 20 ° C. by means of gel permeation chromatography using a concentration-dependent detector, using molecular weight distribution curves calibrated against pullalan standards. The organic compounds (C) preferably contain at least partially functional groups selected from hydroxyl groups, carboxyl groups, phosphate groups, phosphonate groups and amino groups. In a particularly preferred

Embodiment, the sum of acid number and hydroxyl number is at least 100 milligrams KOH per gram, more preferably at least 200 milligrams KOH per gram of organic compounds (C), but preferably not more than 600 milligrams KOH per gram of organic compounds (C).

The acid number is according to the invention an experimentally determined parameter, which is a measure of the number of free acid groups in the polymer or in a polymer mixture. The acid number is determined by adding a weighed amount of the polymer or the

Polymer mixture is dissolved in a solvent mixture of methanol and distilled water in a volume ratio of 3: 1 and then titrated potentiometrically with 0.05 mol / l KOH in methanol. The potentiometric measurement is carried out using a combination electrode (LL-Solvotrode® from Metrohm, reference electrolyte: 0.4 mol / l tetraethylammonium bromide in ethylene glycol). The acid number corresponds to the added amount of KOH in milligrams per gram of polymer or polymer mixture at the inflection point of the potentiometric titration curve.

Analog applies according to the invention that the hydroxyl number as a measure of the number of free

Hydroxyl groups in the polymer or in a polymer mixture experimentally

potentiometric titration can be determined. For this purpose, a weighed amount of the polymer or the polymer mixture in a reaction solution of 0.1 mol / l

Phthalic anhydride in pyridine heated at 130 ° C for 45 minutes and first with the 1, 5 times the volume of the reaction solution of pyridine and then with the 1, 5 times the volume of the reaction solution of deionized water (κ <1 μ8ϋΐη ^{~ 1} ). The liberated amount of phthalic acid is titrated in this mixture by means of 1 M potassium hydroxide solution. The potentiometric measurement is carried out with a combination electrode (LL-Solvotrode® from Metrohm, reference electrolyte: 0.4 mol / l Tetraethylammonium bromide in ethylene glycol). The hydroxyl number corresponds to the added amount of KOH in milligrams per gram of polymer or polymer mixture at the inflection point of the potentiometric titration curve.

Especially for the pretreatment of aluminum in the dry-in-place process

According to the invention, preference is given to those aqueous corrosion inhibitors which are suitable as organic

Compounds (C) copolymers or copolymer blends of alkenes and vinyl alcohol, more preferably of ethene and vinyl alcohol, which particularly preferably have a hydroxyl number in the range of 200 to 500 milligrams KOH per gram of Copoylmers or the copolymer mixture. The proportion of these copolymers or copolymer mixture is preferably at least 0.1% by weight, more preferably at least 0.2% by weight, but preferably does not exceed 5% by weight, more preferably not more than 2% by weight, based in each case aqueous corrosion inhibitors.

The presence of particulate constituents, for example anticorrosion pigments, in the anticorrosive agent brings no significant advantages for further passivation and is rather disadvantageous for the formation of homogeneous thin coatings in the process according to the invention. Accordingly, preference is given to processes according to the invention in which

Corrosion inhibitor less than 0, 1 wt .-%, more preferably less than 0.01 wt .-%, of particulate inorganic constituents are included, which are retained in an ultrafiltration with an exclusion limit of 50 kD in the retentate.

Another advantage of the present invention is that the aqueous

Corrosion inhibitor may be formulated substantially free of toxic heavy metals. In a preferred embodiment, the aqueous corrosion inhibitor therefore contains less than 50 mg / kg, preferably less than 10 mg / kg, more preferably less than 10 mg / kg, of compounds of the element chromium, and in a further preferred embodiment less than 50 mg / kg, preferably less than 10 mg / kg, more preferably less than 1 mg / kg, of compounds of the elements chromium, nickel and cobalt.

The metallic substrates pretreated in the process according to the invention should have a sufficient dissolution pressure in the aqueous corrosion inhibitor under conditions customary in the process for acids and atmospheric oxygen, and thus corrode at least to such an extent that a conversion of the natural or by wet chemical cleaning specifically set thin oxide layer on the respective Metal substrate is initiated, which is completed by the deposition of elements and compounds of the active components of the corrosion inhibitor. Therefore, the pretreatment of such metallic substrates is preferred according to the invention, in a saturated with oxygen potassium hydrogen phthalate buffer (0.05 mol / L, pH 4.01, 20 ° C, 0.21 bar oxygen partial pressure in the atmosphere) a corrosion potential of less as +0.2 V (SHE).

In a particular embodiment of the method according to the invention, the metallic substrates are selected from zinc and / or aluminum and their alloys, particularly preferably from aluminum and its alloys. Alloys are formed in the context of the present invention of such metal substrates containing the respective metal element in a proportion of at least 50 at .-%. Precisely on substrates of the metal aluminum, a particularly effective and homogeneous passivation of the aluminum material can be observed in the process according to the invention, which occurs almost independently of the type of application and is usually carried out in such a way that excellent adhesion to subsequently applied primers containing at least one curable film-forming organic resin results in particular when the film-forming resin has condensation-capable functional groups selected from among phosphonic acid, phosphoric acid, oxirane, amino, hydroxyl and / or carboxyl groups.

The corrosion inhibitor can be brought into contact with the metal substrate by means of conventional methods known to the person skilled in the art of surface treatment. However, an application method which is preferred according to the invention is the setting of a defined wet film on the surface of a preferably flat-shaped metal substrate, for example in the roll application method or by spraying and wiping, and drying it, so that reproducible and always passivating amounts of the active components of the

Corrosion inhibitor remain on the metal substrate.

In this respect, such a method is preferred according to the invention, in which, after contacting the metallic substrate with the aqueous corrosion inhibitor, a wet film of the corrosion inhibitor remains on the surface of the metallic substrate before a subsequent rinsing step or a subsequent wet chemical treatment, preferably by heat Drying (so-called "dry-in-place" process) Drying may be carried out by any technical means which results in liquid components of the wet film having a boiling point of not more than 150 ° C at 1 bar Drying may therefore alternatively be done by passing a dry stream of air through it A wet-chemical treatment in the context of the present invention is any treatment of the substrate with a water-containing agent which does not solely serve in a wet-film containing A Remove ktivkomponenten a previous treatment step from the surface of the metal substrate. Furthermore, for sufficient passivation, in particular on the substrates, zinc and / or aluminum and their alloys are preferred according to the invention in that the wet film of the corrosion protection agent remains on the metal substrate in such a film thickness that, after drying, a coating of zirconium of more than 5 mg / m ² , preferably more than 10 mg / m ² , but preferably less than 150 mg / m ² , more preferably less than 50 mg / m ² .

The particular suitability of the process according to the invention for aluminum and its alloys in conjunction with the preferred application of the corrosion protection agent by application and immediate subsequent drying makes the process according to the invention particularly attractive for the provision of pretreated aluminum strip. A special embodiment of the method according to the invention is therefore the production of coated can ends made of aluminum strip, whose production in a first step on aluminum strip such a wet film of an aqueous corrosion inhibitor containing at least one water-soluble compound (A) zirconium and at least one polycyclic hydrocarbon (B) which has at least one fused benzene ring with in each case at least two ring-substituted hydroxyl groups in ortho-position to each other, realized after drying a coating of zirconium of more than 5 mg / m ² , whereupon after drying the lid material punched out of the band and the Can lid is reshaped. Subsequent to the drying, but preferably before the conversion to the cover material, an organic coating by means of primers containing at least one curable film-forming organic resin which in turn preferably for condensation functional groups selected from phosphonic acid, phosphoric acid, oxirane, amino, hydroxyl and / or carboxyl groups, according to the invention preferably applied and cured. In the present case, a primer for the first coating of the invention pretreated with the anticorrosion agent is used as the primer

Understood metal substrates with an organic material, which necessarily contains at least one curable film-forming organic resin. In the course of

Initial coating with the primer are usually realized layer thicknesses in the range of 0.5 - 50 μιη.

For the inventive method for producing coated can ends from

Aluminum strip are analogous to those already in the context of the general procedure for

corrosion-protective pretreatment of a metallic substrate described in more detail anticorrosive agents preferably use.

In a preferred process of the invention for producing coated aluminum can lids, the primer comprises a curable film-forming organic resin selected from a copolymer or copolymer blend of at least one aliphatic and acyclic alkene with at least one α, β unsaturated carboxylic acid water-dispersed form, wherein the acid value of the copolymer or the copolymer mixture is preferably at least 20 mg KOH / g, but preferably not more than 200 mg KOH / g, and the acid groups of the copolymer or the copolymer mixture in

water-dispersed form preferably present at least 20%, but preferably not more than 60% neutralized.

Alternatively, the curable film-forming organic resin of the primer is preferably selected from an acrylate dispersion obtainable as a reaction product of a terminal or pendant ethylenically unsaturated polymer having preferably a number average molecular weight in the range of 3000-50,000 g / mol, with a mixture of ethylenic unsaturated group-containing monomers including those having carboxyl groups such as (meth) acrylic acid, itaconic acid and crotonic acid. The preparation of such dispersions is described in detail in US 2015/0218407 A1 in paragraphs [0048] - [0049].

Due to the very good paint adhesion, which is achieved by a pretreatment according to the invention based on the anticorrosive agents described above, can be dispensed with special often epoxy-based primer in the packaging area small amounts of hormone toxins, such as bisphenol A, can deliver to the stored food and therefore preferably should not be used. Accordingly, the primers for the first coating of the pretreated aluminum strip for producing can lids are preferably largely free of organic compounds which have a diphenylmethane structural unit and more preferably contain less than 0.1% by weight

Diphenylmethane structural units calculated as C15H14 and based on the total amount of compounds with a boiling point of more than 150 ° C at 1 bar.

In a further aspect, the present invention comprises a concentrate of the above

described corrosion inhibitor, wherein the concentrate has a pH in the range of 0.5 to 2.0 and at least 1 wt .-% of a water-soluble compound (A) of the element zirconium based on the element zirconium and at least 0.01 wt. % of polycyclic hydrocarbons (B) containing at least two fused benzene rings each having at least two nucleus-substituted hydroxyl groups in ortho-position to each other, wherein the

Benzenringe bridged each other by Anellierung to an acyclic hydrocarbon system, wherein the acyclic hydrocarbon system preferably has at least one oxo group or hydroxyl group.

Naturally, the same proportions of water-soluble compounds (A) of the element zirconium and polycyclic hydrocarbons (B) are preferred relative to one another for the concentrate according to the invention as for the corrosion protection agent provided therefrom

inventive method. Optionally, the concentrate contains at least 1% by weight, preferably at least 2% by weight but preferably not more than 20% by weight, more preferably not more than 10% by weight of organic compounds (C) selected are made of copolymers or

Copolymer blends of alkenes and vinyl alcohol, preferably ethene and vinyl alcohol, which in turn each preferably have a hydroxyl number in the range of 200 to 500 milligrams KOH per gram of Copoylmers or the copolymer mixture.

Preferably, in the concentrate according to the invention, the water-soluble compound (A) of the element zirconium is selected from zirconyl nitrate.

Also preferred in the concentrate according to the invention is the polycyclic hydrocarbon (B) selected from 1,2-hydroxyanthraquinone.

The corrosion inhibitor for use in a method of the invention can be prepared by diluting the concentrate by a factor of 5-20.

Inasmuch as it has previously been pointed out for the anticorrosion agent in the described process according to the invention that the same should not contain certain components for ensuring a sufficient passivation above predetermined amounts, this also applies mutatis mutandis to the concentrate according to the invention, wherein the respective upper limits in the concentrate according to the invention by a factor of 5 are higher than for the corrosion inhibitor in the process according to the invention.

EXAMPLES

The effectiveness of the pretreatment according to the invention to form a potential paint adhesion base can be achieved by applying a small amount (about 1 ml) of an acidic aqueous pretreatment solution according to the invention (pH 1, 5) containing 15 g / kg Zr in the form of zirconyl nitrate and 500 mg / kg alizarin On aluminum sheet (Al 3008, 0.2 mm thickness) and subsequent drying at 30 ° C in comparison to a treatment with a solution that does not contain the alizarin detected. While the treatment of the invention provides a non-wipeable iridescent coating, the rather white coating based on the zirconyl nitrate-containing solution alone is easily removed with a cloth.

For the demonstration of the suitability of the pretreatment according to the invention to provide a good Lackhaftgrund different coating systems for can lids have been applied and the paint adhesion, especially paint detachments, the so-called "feathering", and discoloration, the so-called "blushing" after removal under sterilization conditions, which a coating, a Material that is suitable for the storage of food and therefore in direct contact with food is usually withstand, assessed.

Table 1 lists the various pretreatments and primer coatings tested in this regard. The pretreatment was carried out in alkaline (Bonderite® C-AK 1803 from Henkel AG & Co.KGaA, 15 g / L, 60 ° C., 10 s), cleaned aluminum foil washed with deionized water (κ <1 μ8ατΓ) (Al 3006 ) with a thickness of 0.2 mm and for this purpose a wet film of the pretreatment solution of about 4-6 ml / m ² applied and dried at 80 ° C, so that the coating layer of zirconium each 12 mg / m ² . The organic primer was knife-dried immediately after the drying step and dried at 249 ° C PMT (Peak Metal Temperature) and cured, with a dry film coating of primer of about 12 g / m ^{2 was} set.

The aging of the thus coated aluminum sheets under sterilization conditions was carried out at 121 ° C with tap water or in tap water containing 2 wt .-% pure

Citric acid for 30 minutes in an autoclave. An assessment of the lacquer detention on the cross-cut according to DIN EN ISO 2409 and the "blushing", ie the appearance of whitish discolorations, was then carried out The results are summarized in Tab. Table 1

Experiment no. Pretreatment primer

Zirconyl nitrate: 6 g / kg

E1 Alizarin: 0.08 g / kg epoxy dispersion ³

Ethylene-vinyl alcohol copolymer: 4.8 g / kg

Zirconyl nitrate: 6 g / kg

E2 Alizarin: 0.08 g / kg Acrylate dispersion ⁴

Ethylene-vinyl alcohol copolymer: 4.8 g / kg

CE1 base: Bonderite® MNT-802 N ² epoxy dispersion ³

CE2 base: Bonderite® MNT-802 N ² acrylate dispersion ⁴

Degree of hydrolysis 93 mol%

10% strength by weight aqueous solution of the commercial product (Henkel AG & Co.)

Co.KGaA) containing H2ZrF6 and polyacrylic acid in a weight ratio of 1, 23: 1 2489-814 (PPG)

2466-810 (PPG)

It can be seen that the pretreatment according to the invention, especially for the coating based on the acrylate-based primer, gives excellent paint adhesion values compared with a conventional fluorozirconate-based pretreatment, while for a coating based on the epoxy-based primer at least equally good results both with regard to paint adhesion as well as "blushing". Table 2

according to DIN EN ISO 2409 (0-5)

0: no discoloration

1: less than 10% of the area is discolored, single areas 2: less than 20% of the area is discolored, single areas 3: at least 20% of the area is discolored; Striped 4: at least 40% of the area is discolored

5: at least 60% of the area is discolored

Claims

claims

A process for the anticorrosive pretreatment of a metallic substrate, in which the surface of the metallic substrate is brought into contact with an aqueous anticorrosion agent containing at least one water-soluble compound (A) of zirconium, characterized in that the agent additionally comprises at least one polycyclic hydrocarbon (B) containing at least one fused benzene ring each having at least two nucleus-substituted hydroxyl groups in ortho position to each other.

2. The method according to claim 1, characterized in that the polycyclic

Hydrocarbon (B) at 20 ° C in deionized water having a conductivity of less than Ι μβαττ ^{1 has} a solubility of less than 5 g / kg, preferably less than 1 g / kg.

3. The method according to one or both of the preceding claims, characterized in that the polycyclic hydrocarbon (B) at least two fused benzene rings each having at least two nucleus-substituted hydroxyl groups in ortho-position to each other, wherein the benzene rings each bridged by Anellierung to an acyclic hydrocarbon system wherein the acyclic hydrocarbon system

preferably has at least one oxo group or hydroxyl group.

4. The method according to one or more of the preceding claims, characterized in that the polycyclic hydrocarbon (B) is selected from the group of nuclear-substituted with at least two hydroxyl groups in the ortho-position

Anthraquinones, preferably from 1, 2-hydroxyanthraquinone.

5. Method according to one or more of the preceding claims, characterized in that the source of the water-soluble compound (A) of the element zirconium is not also a source of fluoride ions and is preferably selected from zirconyl nitrate,

Zirconium acetate and / or ammonium zirconium carbonate, particularly preferably from

Zirconyl.

6. The method according to one or more of the preceding claims, characterized in that the total fluoride content in the aqueous phase of the anticorrosion agent is less than 50 mg / kg, preferably less than 10 mg / kg, more preferably less than

1 mg / kg.

7. The method according to one or more of the preceding claims, characterized in that the weight ratio of water-soluble compounds (A) of the element zirconium based on the element zirconium to polycyclic hydrocarbon (B) less than 0.2, preferably less than 0, 1, however, preferably greater than 0.02.

8. The method according to one or more of the preceding claims, characterized in that the pH of the anticorrosion agent is less than 2.0, more preferably less than 1, 6, but preferably greater than 0.5, more preferably greater than 1, 0 is.

9. The method according to one or more of the preceding claims, characterized in that in the anticorrosion agent additionally at least 0.1 wt .-%, preferably at least 0.2 wt .-%, of organic compounds (C) in each case based on the aqueous

Corrosion inhibitors are included, which have a molecular weight above 5,000 g / mol and preferably at least partially functional groups selected from hydroxyl groups, carboxyl groups, phosphate groups, phosphonate groups and amino groups, wherein the sum of acid number and hydroxyl number preferably at least

100 milligrams of KOH per gram, but preferably not more than 600 milligrams of KOH per gram of organic compounds (C).

10. The method according to claim 9, characterized in that the organic compounds (C) are selected from copolymers or copolymer blends of alkenes, preferably ethene, and vinyl alcohol, preferably having a hydroxyl number in the range of 200 to 500 milligrams KOH per gram of Copoylmers or the copolymer mixture, wherein the proportion of these copolymers or copolymer mixture is preferably not

5 wt .-%, particularly preferably not 2 wt .-% in each case based on the aqueous

Exceeds anticorrosion agent.

1 1. Method according to one or more of the preceding claims, characterized in that the metallic substrates are selected from zinc and / or aluminum, preferably of aluminum.

12. The method according to one or more of the preceding claims, characterized in that after contacting the metallic substrate with the aqueous corrosion inhibitor remains a wet film on the surface of the metallic substrate, before a subsequent rinsing step or a subsequent wet-chemical

Treatment, preferably by heat, is dried.

13. The method according to claim 12, characterized in that the wet film remains in such a film thickness that after drying a layer of zirconium more than 5 mg / m ² , preferably more than 10 mg / m ² , but preferably less than 150 mg / m ² , more preferably less than 50 mg / m ² results.

14. A method for producing coated can ends made of aluminum strip, wherein first in a first step on aluminum strip, a layer of zirconium more than

5 mg / m ² according to the method of claim 13 and optionally subsequently applying a primer and cured, after which the lid material is punched out of the strip and formed to the can lid.

15. Concentrate of a corrosion inhibitor having a pH in the range of 0.5 to 2.0 containing at least 1 wt .-% of a water-soluble compound of the element zirconium based on the element zirconium and at least 0.01 wt .-% of polycyclic hydrocarbons with at least two fused benzene rings each having at least two nucleus-substituted hydroxyl groups in ortho-position to each other, wherein the benzene rings each bridged by Anellierung to an acyclic hydrocarbon system bridged, wherein the acyclic hydrocarbon system preferably has at least one oxo group or hydroxyl group.