EP2917383B1 - Can pretreatment for improved coat adhesion - Google Patents

Description

The present invention relates to the use of an aqueous composition for the pretreatment of can sheets in the course of which an inorganic-organic conversion layer is formed, which as such provides an excellent sliding behavior of the molded can sheets and also provides an excellent primer for subsequent painting. The invention encompasses a method in which the can sheet pressed to the half-open can-cylinder is brought into contact with an acidic aqueous composition before further forming processes, the water-soluble inorganic compounds of the elements Zr, Ti, Si, Hf or Ce, water-soluble polymers with carboxyl groups or hydroxyl groups and a dispersed wax. Both the outer and inner surfaces of metallic can-type cylinders can be pretreated in the process according to the invention. Furthermore, the invention relates to an acidic aqueous composition which is particularly suitable in the pretreatment process and comprises water-soluble polymers selected from condensation products of glycoluril and aldehydes. Furthermore, a production method for can-type cylinders comprising the pretreatment according to the invention is described.

Cans made of tinned steel (tinplate) and aluminum (or aluminum alloys, hereinafter referred to as "aluminum" for simplicity) and steel are widely used for storing food and especially beverages. In the process of can production these are usually degreased after deep drawing of the can plate to the can cylinder, washed and usually pretreated corrosion protection, including, for example, acidic or alkaline cleaners and passivation solutions are commercially available. At least the detergent solutions must have sufficient dissolving power for the metals of interest to effectively remove metal debris from the cans. By means of the cleaning pickling attack, the can surface is usually roughened to such an extent that a certain surface roughness remains even in the case of subsequent corrosion-protecting pretreatment by means of passivation solutions. This roughness of the outer surface of the cylindrical cans causes friction between contacting cans and between cans and Devices for receiving and further forming the can cylinder is increased. This friction causes in the transfer of the cans from one to the next manufacturing step regularly losses in transport and process speed, for example, by downtime especially in places where forms a doses back by separating the cans, or by slowing the recording and forming processes of can cylinders in the subsequent process steps until the completion of the beverage can. Since this reduces the capacity of the production plant, it is endeavored to condition the canned surfaces so that the friction between touching doses is minimized. For this purpose, the can-type cylinders are provided with a friction-reducing coating, which is usually applied in a conditioning sink following the anti-corrosive pretreatment. In this rinsing step, the can barrel is wetted with a mostly aqueous solution of special surfactants and / or organic substances which increase the sliding properties of the metal surface. Such substances are referred to in the art of canning as a "mobility enhancer". The pretreatment of the cancans thermoformed to the cancylinder therefore usually involves several wet-chemical treatment steps, so that in addition to the degreasing or cleaning and the corrosion-protective pretreatment, a surface conditioning of the outer jacket surface of the cancans is carried out by means of a sink containing "Mobility Enhancer".

However, the application of a friction-reducing layer must not result in the adhesion suffering from coatings, inscriptions or other coatings applied for corrosion protection and / or decorative reasons. In particular, when necking and the subsequent shaping of the cylinder edge to the flare, there may be no damage to the paint due to lack of paint adhesion. Especially in this forming process, however, paint chipping are often observed, so that damaged can-type cylinders must be sorted out.

The US 4,859,351 describes such surface conditioning of metallic cans to reduce frictional resistance containing water-soluble organic ethoxylated phosphate esters, alcohols and / or fatty acids, which are characterized by their compatibility with a subsequent coating. From the US 6,040,280 Also, a surface conditioning based on ethoxylated fatty acid esters and polyoxyalkylene ethers for aluminum cans, which does not adversely affect the subsequent coating and immediately follows a chromium-containing conversion treatment.

Furthermore, it must be ensured during the surface treatment and coating of the can-type cylinders that the different requirements with respect to corrosion resistance are met depending on the contents of the cans. In this case, only those active ingredients are to be used, which are generally ecologically and food safe in particular harmless. This concerns the selection of the active components in the surface treatment as well as the selection of the binder in the exterior and interior painting of the cans cylinder and this regardless of whether technically only the treatment of the outer can surfaces is provided, since it is often used for production-economic reasons in the spray process, at a certain Materialumgriff in the interior of the can cylinder can not be completely avoided.

The prior art discloses various chromium-free processes for the corrosion-protective pretreatment of metallic cans, which generally employ inorganic acids, in particular phosphoric acid, hydrofluoric acid or other sources of fluoride and / or complex fluorides, and which operate with or without the additional use of organic polymers.

For example, this describes US-A-4,992,116 an aqueous acidic processing solution containing phosphate, a fluoro acid of Zr, Ti, Hf or Si and a polyphenol compound which is a Mannich adduct of a substituted amine to a polyalkylene phenol or a tannin. The WO 2007-A-113141 discloses a method of surface treating metal sheets or shaped aluminum metal sheets with an aqueous composition containing phosphate, complex fluorides of Zr, Ti, Hf, and optionally another component.

The EP-B-8942 discloses treatment solutions, preferably for aluminum doses, comprising a) from 0.5 to 10 g / l of polyacrylic acid or an ester thereof and b) from 0.2 to 8 g / l of at least one of hexafluorozirconic acid, hexafluorotitanic acid or hexafluorosilicic acid.

The object of the present invention is therefore to provide a method for the surface treatment of metal cans, which on the one hand has an improved performance spectrum with regard to the aforementioned different requirements and on the other hand enables as little process steps as possible to condition the can cylinders. In particular, the sliding and forming behavior of the cans deep-drawn cans should be further improved and at the same time an excellent anti-corrosion primer for a protective coating can be provided.

1. a) 0,001-1g/l zumindest eine wasserlösliche Verbindungen der Elemente Zr, Ti, Si, Hf und/oder Ce, bezogen auf die Gesamtheit der vorgenannten Elemente,
2. b) 0,1-50g/l zumindest ein wasserlösliches organisches Harz, das zumindest Carboxyl-Gruppen oder Hydroxyl-Gruppen aufweist, wobei die Summe aus Säurezahl und/oder Hydroxylzahl des jeweiligen Harzes zumindest 50 mg KOH/g beträgt und
3. c) 0,1-10g/l zumindest einen dispergierten Wachs enthält.

This object is achieved by a process for the surface treatment of a deep-drawn aluminum sheet open on one side can cylinder, in which at least the outer surface of the can barrel is brought into contact with an acidic aqueous composition, the

1. a) 0.001-1g / l at least one water-soluble compound of the elements Zr, Ti, Si, Hf and / or Ce, based on the totality of the aforementioned elements,
2. b) 0.1-50 g / l at least one water-soluble organic resin having at least carboxyl groups or hydroxyl groups, wherein the sum of acid number and / or hydroxyl number of the respective resin is at least 50 mg KOH / g and
3. c) 0.1-10 g / l contains at least one dispersed wax.

An inorganic compound is water-soluble in the sense of the present invention, if at a temperature of 20 ° C 50 g of the inorganic compound in a kilogram of water can be solved with a pH of 3, without forming an insoluble soil body in the aqueous phase ,

An organic polymer is water-soluble in the context of the present invention, when at a temperature of 20 ° C, 10 g of the polymer can be dissolved in one kilogram of water having a pH of 3 and further a clear solution is present. A clear solution is when the turbidity value (NTU) measured according to DIN ISO 7027 at a wavelength of 860 nm in the scattered light method at a temperature of the solution of 20 ° C below a value of 50.

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 dissolving a weighed quantity of the polymer or the polymer mixture in a solvent mixture of methanol and distilled water in the volume ratio 3: 1 and then titrating 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 per gram of polymer or polymer mixture at the inflection point of the potentiometric titration curve.

Analogously, according to the invention, the hydroxyl number can be determined experimentally by potentiometric titration as a measure of the number of free hydroxyl groups in the polymer or in a polymer mixture. For this purpose, a weighed amount of the polymer or the polymer mixture is heated in a reaction solution of 0.1 mol / l phthalic anhydride in pyridine at 130 ° C for 45 minutes and first with 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 μScm ^-1 ). The liberated amount of phthalic acid is titrated in this mixture by means of 1 M sodium hydroxide solution. 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 hydroxyl number corresponds to the added amount of NaOH per gram of polymer or polymer mixture at the inflection point of the potentiometric titration curve.

For the purposes of the present invention, a wax refers to organic substances which are kneadable at 20 ° C., solid to brittle, have a coarse to finely crystalline structure, are translucent to opaque in color but are not glassy, melt above 40 ° C. without decomposition , slightly above the melting point are slightly liquid (less viscous), have a strong temperature-dependent consistency and solubility and can be polished under light pressure. If more than one of the above properties is not met, the organic matter is not wax.

The inventive method initially causes good corrosion protection of the outer surfaces of the can barrel and beyond due to the mixed organic-inorganic conversion layer a good paint adhesion, which is surprisingly not reduced by the wax content. The wax also adheres very well to the outer surfaces and is not removed by subsequent rinsing steps. The good adhesion of the waxes in turn increases the mobility of the can cylinders in the industrial can production, especially in the outlet of individual production steps, since the friction of touching shell surfaces of the can cylinder is significantly reduced, so that high transport and thus the production speeds can be ensured. Moreover, according to the invention pretreated and provided with a protective varnish can cylinder on an excellent forming behavior, wherein Lackabplatzungen at the tapering ("necking") occur at the open edge of the can barrel and shaping thereof to the flare less frequently and to a much lesser extent.

The method according to the invention is therefore particularly advantageous for reshaping in the edge region at the open end of the can barrel, comprising any such forming which is directly necessary for establishing a connection of the can barrel with a closure cap, for example drawing the open end of the can barrel for rejuvenation the diameter of the can barrel in the edge region ("necking") and / or the molding of the can barrel to the flare.

According to the invention are processes in which the content of water-soluble inorganic compounds of the elements Zr, Ti, Si, Hf and / or Ce according to component a) in the acidic aqueous composition in the range of 0.01-1 g / l based on the total of above-mentioned elements, wherein the proportion of water-soluble inorganic compounds of the elements Zr and / or Ti is at least 0.01 g / l, more preferably at least 0.02 g / l based on the totality of the elements Zr and Ti.

It is further preferred in this context for the water-soluble compounds according to component a) of the acidic aqueous composition to be selected from fluorocomplexes of the elements Zr, Ti and / or Si, more preferably from fluorocomplexes of the elements Zr and / or Ti.

For the purposes of the present invention, fluoro complexes are understood as meaning complexes with the corresponding abovementioned metallic or semimetallic elements which have at least one fluorine atom as ligands and are present in aqueous solution as anions.

The proportion of the organic resins to be used in the process of the invention in component b) in the acidic aqueous composition is in the range of 0.1-50 g / l, more preferably in the range of 0.5-10 g / l.

The water-soluble organic resin according to component b) of the acidic aqueous composition to be used in the process according to the invention is preferably selected from polymers or copolymers based on vinyl ethers, vinyl alcohols, (meth) acrylic acid, maleic acid or fumaric acid, from polyesters containing hydroxyl groups and from condensation products of glycoluril or melamine with aldehydes, particularly preferably organic resins are the condensation products of glycoluril or melamine with aldehydes, in particular condensation products of glycoluril with aldehydes having a hydroxyl number of preferably at least 50 mg KOH / g. The degree of alkylation of the condensation products of glycoluril or melamine with aldehydes is preferably below 20%, more preferably below 10%. For the aforementioned condensation products, it is true that primary aldehydes are preferred, in particular acetaldehyde and formaldehyde.

The wax used in the process according to the invention is preferably selected from synthetic waxes, particularly preferably from oxidized polyalkylene waxes, particularly preferably from oxidized polyethylene waxes. In order to ensure sufficient sliding properties of the outer lateral surfaces of the can barrel when in contact with other cans or with picking tools in the can production, the content of waxes in the acidic aqueous composition is at least 0.1 g / l, more preferably at least 1 g / l, so that it is ensured that a sufficient amount of the wax can be applied to the outer surfaces of the can barrel. For reasons of economy of the process according to the invention, the proportion of waxes in the acidic aqueous Composition not greater than 10 g / l.

Furthermore, it is preferred that the acidic aqueous composition additionally contains phosphate ions, preferably in an amount of at least 0.1 g / l, in the process according to the invention. The use of phosphates improves the corrosion protection properties of the mixed organic-inorganic conversion layer. The proportion of phosphate ions preferably exceeds 10 g / l for reasons of economy of the process and to avoid phosphate sludge.

The pH of the acidic aqueous composition in the process according to the invention is preferably not less than 2, more preferably not less than 3, and preferably not greater than 6, particularly preferably not greater than 5.

In the process of the present invention, preferably, immediately after contacting with the acidic aqueous composition, a rinsing step is carried out to remove excess active components of the acidic aqueous composition which are not incorporated into or adhered to the mixed organic-inorganic conversion layer.

A rinsing step in the sense of the present invention is used, unless otherwise stated, exclusively for the removal of a wet liquid adhering to the surface of the can containing the active components from a previous wet-chemical treatment step. A rinsing step is therefore preferably carried out with water, wherein the rinse water preferably has a drying residue of less than 1 g / l, particularly preferably less than 100 ppm, particularly preferably less than 10 ppm.

The process according to the invention is usually followed by further wet-chemical treatment steps, which ultimately comprise the coating of the can barrel with a can varnish. When applying the can varnish, a distinction is made in can production between inner and outer varnishes. The process of the invention provides a suitable paint adhesion-promoting and Corrosion-protecting pretreatment for the application of both exterior and interior paints.

In a preferred method according to the invention, therefore, at least the outer jacket surface of the can cylinder open on one side is provided with a protective lacquer after being brought into contact with the acidic aqueous composition and optionally after an immediately following flushing step.

Since tin can paints are often in contact with food, special requirements are placed on the coating of the can interior surfaces. In the prior art, for example, there is a departure from the use of bisphenol A based epoxy resins as can interior lacquer instead. Several national legislative initiatives, including those initiated by EU Directive 2002/72 / EU, set maximum limits for the migration of bisphenol A from outer packaging to food. Since in the paint application on the can outer surfaces a wrapper of the most sprayed paint in the can interior process technology can not be completely avoided, food-grade paints are preferably used for the paint in the exterior of the can. It has now been found that the method according to the invention is particularly suitable for those conformal coatings whose binders are based on acrylate resins and polyester resins.

In a preferred method according to the invention for the surface treatment of deep-drawn cancylinders, therefore, at least the outer surface of the unidirectional can cylinder is provided with such protective lacquers whose binders are selected from acrylate resins and / or polyester resins, the acrylate resins preferably being copolymers of alkenes, in particular ethene, propene, 1 Butene, 2-butene, isobutene, 1,3-butadiene and / or 2-methylbuta-1,3-diene, and α, β-unsaturated carboxylic acids, in particular cinnamic acid, crotonic acid, fumaric acid, itaconic acid, maleic acid, acrylic acid and / or methacrylic acid, consist.

Since in the method according to the invention a very low coefficient of sliding friction results on the pretreated outer lateral surfaces of the can barrel, there is no need for additional conditioning of the can cylinders to improve the Slip properties, for example by contacting with other liquids containing mobility enhancers, for example dispersed waxes. A preferred method according to the invention is therefore characterized in that no further wet-chemical pretreatment steps, which are not rinsing steps, are carried out after bringing the can cylinder open on one side with the acidic aqueous composition and before applying the protective lacquer.

The bringing into contact of the acidic aqueous compositions with the outer lateral surfaces of the can cylinders and the application of the protective lacquer are preferably carried out in the process according to the invention by spraying, for example by the airless method.
In the so-called airless method, the respective liquids are atomized airless and applied to the material surface. In these spraying methods, a predetermined amount of the liquid, while the can rotates about its own longitudinal axis to form a homogeneous wet film, is applied by means of spray guns.

After application of the wet film for coating with a protective varnish, the unilaterally opened can-type cylinders treated in this way are preferably cured at temperatures in the range from 120 ° C. to 200 ° C. (object temperature) to form a paint film.

The wet-chemically pretreated in such a method according to the invention and provided with a protective varnish, open on one side cans are usually formed in the later course of can making in one-sided open edge area, in particular for tapering the diameter of the can barrel fed in the edge region ("necking") and formed to the flare ,
The improved forming behavior of the can-type cylinders, which is mediated in addition to corrosion protection, paint adhesion and low lubricity, is therefore only used technically if the aforementioned forming process is followed by wet-chemical pretreatment according to the process of the invention.
The method according to the invention for surface treatment is therefore preferably characterized in that the bringing into contact with the acidic aqueous composition and an optionally subsequent step for applying a Protective varnish is carried out only on such unilaterally open can cylinders, which are not reshaped in the edge area open on one side, in particular there neither retracted for rejuvenation of the diameter of the can cylinder nor formed to the flare. The unidirectionally open can-end cylinders used in the method according to the invention for surface treatment are preferably deep-drawn from tinplate, sheet steel or aluminum sheet.

Furthermore, the present invention comprises a particularly suitable acidic aqueous composition for wet-chemical pretreatment in the process according to the invention for the surface treatment of can-open cans.

1. a) 0,005-0,5 Gew.-%, vorzugsweise 0,01-0,1 Gew.-%, an Fluorokomplexen der Elemente Zr, Ti und/oder Si,
2. b) 0,1-5 Gew.%, vorzugsweise 0,2-1 Gew.-%, an oxidierten Polyalkylenwachsen,
3. c) 0,05-3 Gew.-%, vorzugsweise 0,1-2 Gew.-%, an wasserlöslichen Harzen ausgewählt aus Kondensationsprodukten von Glycoluril mit Aldehyden, wobei das Kondensationsprodukt vorzugsweise eine Hydroxylzahl von zumindest 50 mg KOH/g aufweist und der Alkylierungsgrad des Kondensationsproduktes vorzugsweise kleiner als 20 % ist.

Such an acidic aqueous metallic surface-treating composition of the present invention has a pH in the range of 2 to 5 and contains

1. a) 0.005-0.5% by weight, preferably 0.01-0.1% by weight, of fluorocomplexes of the elements Zr, Ti and / or Si,
2. b) 0.1-5% by weight, preferably 0.2-1% by weight, of oxidized polyalkylene waxes,
3. c) 0.05-3 wt .-%, preferably 0.1-2 wt .-%, of water-soluble resins selected from condensation products of glycoluril with aldehydes, wherein the condensation product preferably has a hydroxyl value of at least 50 mg KOH / g and the Alkylierungsgrad the condensation product is preferably less than 20%.

For the condensation product primary aldehydes are preferred, in particular acetaldehyde and formaldehyde.

The acidic aqueous composition according to the invention preferably contains less than 0.1 wt .-% of organic polymers from the group of epoxies, urethanes and polyesters, preferably less than 0.1 wt .-% of such organic polymers containing no condensation products of glycoluril with Represent aldehydes.

1. (A) eine Ronde eines Metallblechs zu einem einseitig offenen Dosenzylinder tiefgezogen wird;
2. (B) der einseitig offene Dosenzylinder nasschemisch vorbehandelt und anschließend
   • mit oder ohne dazwischenliegendem Spülschritt, jedoch vorzugsweise ohne weitere dazwischenliegende nasschemische Vorbehandlungsschritte, die keine Spülschritte sind - lackiert wird, wobei in der nasschemischen Vorbehandlung zumindest die äußere Mantelfläche des Dosenzylinders mit einer sauren wässrigen Zusammensetzung enthaltend
     1. a) zumindest eine wasserlösliche anorganische Verbindungen der Elemente Zr, Ti, Si, Hf und/oder Ce;
     2. b) zumindest ein wasserlösliches organisches Polymer, das zumindest Carboxyl-Gruppen oder Hydroxyl-Gruppen aufweist, wobei die Summe aus Säurezahl und/oder Hydroxylzahl zumindest 50 mg KOH/g beträgt; und
     3. c) zumindest einen dispergierten Wachs
     in Kontakt gebracht wird;
3. (C) der nasschemisch vorbehandelte und lackierte Dosenzylinder zur Verjüngung des Durchmessers des Dosenzylinders im einseitig offenen Randbereich eingezogen und/oder im einseitig offenen Randbereich zum Bördel ausgeformt wird.

The present invention also relates to a manufacturing method for can-type cylinders in which

1. (A) a blank of a metal sheet is deep-drawn to a unilaterally open cancylinder;
2. (B) the unilaterally open can cylinder wet-chemically pretreated and then
   • with or without intermediate rinsing step, but preferably without further intervening wet-chemical pretreatment steps which are not rinsing steps - is painted, wherein in the wet-chemical pretreatment containing at least the outer surface of the can barrel with an acidic aqueous composition
     1. a) at least one water-soluble inorganic compounds of the elements Zr, Ti, Si, Hf and / or Ce;
     2. b) at least one water-soluble organic polymer having at least carboxyl groups or hydroxyl groups, wherein the sum of acid number and / or hydroxyl number is at least 50 mg KOH / g; and
     3. c) at least one dispersed wax
     is brought into contact;
3. (C) the wet-chemically pretreated and lacquered can cylinder is retracted for the purpose of narrowing the diameter of the can barrel in the edge region which is open on one side and / or is formed into the flared edge region on one side.

After deep-drawing of the blank to open on one side can-cylinder is preferably carried out a cleaning step for the removal of metalworking fluids.

For the wet-chemical pretreatment used in the manufacturing method for can-type cylinders according to the invention and the subsequent coating with a protective varnish, the same preferred embodiments apply as described above for the surface-treatment process according to the invention. The same applies to the methods for contacting the compositions in the pre-treatment and painting of the can-type cylinders and the material selection of the metal sheets.

EXAMPLES

• 50 ppm Zr aus H₂ZrF₆
• 40 ppm B aus Borsäure
• 80 ppm PO₄ aus Phosphorsäure
• 300 ppm NO₃ aus Salpetersäure
• 25 ppm freies Fluorid (gemessen mit ionenselektiver Elektrode)
• pH-Wert 3,2

As a basic formulation for the pretreatment of aluminum cans (EN AW-3104) an acidic aqueous treatment solution with the following composition was used:

• 50 ppm Zr from H ₂ ZrF ₆
• 40 ppm B from boric acid
• 80 ppm PO ₄ from phosphoric acid
• 300 ppm NO ₃ from nitric acid
• 25 ppm free fluoride (measured with ion-selective electrode)
• pH 3.2

• Org1: Tetramethylolglycoluril-Harz (Hydroxylzahl 450-480 mg KOH/g)
• Org2: Maleinsäure-Methylvinylether-Copolymer (Säurezahl 220-280mg KOH/g)
• Org3: Polyacrylsäure

Pre-treatment compositions according to the invention additionally contained an organic polymer and an emulsified, nonionic oxidized polyethylene wax. The following organic polymers were used:

• Org1: tetramethylolglycoluril resin (hydroxyl number 450-480 mg KOH / g)
• Org2: maleic acid-methyl vinyl ether copolymer (acid number 220-280 mg KOH / g)
• Org3: polyacrylic acid

The outer surfaces of the aluminum cans were sprayed with the treatment solutions listed in Table 1, then rinsed with deionized water (κ <1μScm ^-1 ) and dried at 60 ° C object temperature. Table 1 Formulations for the surface treatment of aluminum cans Example no. Polymer in g / l Wax in g / l Layer ¹ on Zr Org1 org2 Org3 mg / m ² V1 - - - - 17 V2 - - - 7 18 V2 6 - - - 17 E1 6 - - 7 20 E2 - 6 - 7 18 E3 - - 6 7 21 ¹ measured by X-ray fluorescence analysis (RFA)

The properties of the conversion coatings obtained after pretreatments with acidic compositions according to Table 1 are given in Table 2 regarding slip behavior and paint adhesion.

The sliding behavior was determined by stacking three cans in the shape of a triangle with the lower two cans forming the base raised at one end vertical to the longitudinal direction of the can. When lifting the stack of cans one-sidedly, the angle between the can axis and the horizontal is given as a "slip angle", in which the upper can starts to slide off. This test was repeated five times with different but similarly pretreated doses and the average of the particular "slip angle" formed.

1. 1: keine sichtbaren Risse oder Lackabplatzungen
2. 2: Risse und leichte Lackabplatzungen
3. 3: starke Lackabplatzungen

Tab. 2 Gleitverhalten und Lackhaftung der gemäß Tabelle 1 vorbehandelten äußeren Dosenflächen Beispiel-Nr. Slip Angle Lackhaftung V1 35 3 V2 35 3 V2 39 2 E1 22 1 E2 25 1-2 E3 30 1-2 The paint adhesion was after the exterior painting of the pretreated cans with a commercially available can varnish (paint base: acrylate-modified polyester, DSM, Uradil ® SZ250, layer thickness about 15 microns) and after the rejuvenation or compression of the open can edge ("necking") and 90 ° flanging of the edge of the can. The evaluation was carried out visually in the forming area of the can according to the following criteria for every five cans:

1. 1: no visible cracks or paint flaking
2. 2: Cracks and light paint flaking
3. 3: strong paint chips

Tab. 2 Sliding behavior and paint adhesion of the pretreated according to Table 1 outer can surfaces Example no. Slip Angle paint adhesion V1 35 3 V2 35 3 V2 39 2 E1 22 1 E2 25 1-2 E3 30 1-2

The results show that with pretreatment compositions according to the invention, in particular with compositions containing the glycoluril resin, the lowest slip Angle and the best paint adhesion are achieved (E1-E3).

Claims (13)

1. A method for treating the surface of a deep-drawn can cylinder that is made of aluminium sheet and is open at one end, in which at least the outer lateral surface of the can cylinder is brought into contact with an acidic, aqueous composition containing:

   a) from 0.01 to 1 g/l of at least one water-soluble compound of the elements Zr, Ti, Si, Hf and/or Ce, based on all of the aforementioned elements as a whole,

   b) from 0.1 to 50 g/l of at least one water-soluble organic resin, which at least comprises carboxyl groups or hydroxyl groups, wherein the sum of the acid number and/or hydroxyl number of each resin is at least 50 mg KOH/g, and

   c) from 0.1 to 10 g/l of at least one dispersed wax.
2. The method according to claim 1, characterized in that the water-soluble compounds according to component a) of the acidic aqueous composition are selected from fluor complexes of the elements Zr, Ti and/or Si.
3. The method according to one or both of the preceding claims, characterized in that the proportion of water-soluble compounds of the elements Zr and/or Ti is at least 0.01 g/l, particularly preferably at least 0.02 g/l based on all of the elements Zr and Ti as a whole.
4. The method according to one or more of the preceding claims, characterized in that the water-soluble organic resin according to component b) of the acidic aqueous composition is selected from polymers or copolymers based on vinyl ethers, vinyl alcohols, (meth)acrylic acid, maleic acid or fumaric acid, from polyesters containing hydroxyl groups and from condensation products of glycoluril or melamine with aldehydes.
5. The method according to one or more of the preceding claims, characterized in that the content of water-soluble organic resins according to component b) in the acidic aqueous composition is preferably in the range of from 0.5 to 10 g/l.
6. The method according to one or more of the preceding claims, characterized in that the wax in the acidic aqueous composition is selected from synthetic waxes, preferably from oxidized polyalkylene waxes, particularly preferably from oxidized polyethylene waxes.
7. The method according to one or more of the preceding claims, characterized in that the acidic aqueous composition also contains phosphate ions, preferably in an amount of at least 0.1 g/l, but preferably no more than 10 g/l phosphate ions.
8. The method according to one or more of the preceding claims, characterized in that the acidic aqueous composition has a pH of no less than 2, preferably no less than 3 and no more than 6, preferably no more than 5.
9. The method according to one or more of the preceding claims, characterized in that at least the outer lateral surface of the can cylinder than is open at one end is provided with a protective coating after being brought into contact with the acidic aqueous composition and optionally after a rinsing step that is carried out immediately thereafter.
10. The method according to claim 9, characterized in that, after bringing the can cylinder that is open at one end into contact with the acidic aqueous composition and before applying the protective coating to the outer lateral surface of the can cylinder, no additional wet-chemical pre-treatment steps that are not rinsing steps are carried out.
11. The method according to one or more of the preceding claims, characterized in that the can cylinder is not worked in the edge region that is open at one end, in particular is neither swaged at the edge region in order to taper the diameter of the can cylinder, nor shaped to form a rim.
12. A production method for a can cylinder, in which

    (A) a circular blank of aluminium sheet is deep-drawn to form a can cylinder open at one end,

    (B) the can cylinder open at one end is pre-treated and coated in a method according to claim 9 or 10,

    (C) the pre-treated and coated can cylinder is swaged in the edge region open at one end in order to taper the diameter of the can cylinder and/or is shaped in the edge region open at one end to form a rim.
13. Acidic aqueous composition having a pH in the range of from 2 to 5 for treating the surface of metal cans, containing

    a) from 0.005 to 0.5 wt.% fluor complexes of the elements Zr, Ti and/or Si,

    b) from 0.1 to 5 wt.% oxidized polyalkylene waxes, and

    c) from 0.05 to 3 wt.% water-soluble resins selected from condensation products of glycoluril with aldehydes.