EP2802688B1 - Method for passivating tinplate - Google Patents

Description

The invention relates to a method for passivating the surface of tin-plated steel strips, which are moved at a belt speed through a coating plant, by anodic oxidation and post-treatment of the tinned steel strip with a chromium-free aftertreatment agent. The invention further relates to the use of complex-linked transition metal agents or organic additives normally used to disperse or improve wetting, as a chromium-free aftertreatment agent in the manufacture of tinned steel strips. The invention further relates to a tin-plated steel strip or sheet with a carrier layer of a fine or Feinstblech made of steel and a deposited thereon tin layer and a surface layer of a chromium-free aftertreatment agent.

Tinplate is a versatile, economically and ecologically advantageous material that is mainly used in the packaging industry. Tinplate is cold-rolled steel sheet with a thickness of up to 0.5 millimeters, which is coated with a thin layer of tin to protect the steel sheet from corrosion. The tin layer is, for example, applied electrolytically to the metal sheet.

In the production of tinned steel sheet, especially in electrolytically working strip tinning, the coated steel sheet is chemically or electrochemically passivated and then greased to make the tin-plated steel resistant to oxidation and to lower the coefficient of friction, so that the tinned steel during subsequent processing, eg. in the production of tinplate packaging for food, can be processed better. The passivation is usually carried out using Cr ⁶⁺ -containing solutions. The use of chromium-containing agents in the treatment of metal products is environmentally harmful and should therefore be regulated by law, in particular for metal products intended for the food industry.

State of the art

For this reason, the prior art has proposed Cr ⁶⁺ -free passivation solutions. For example disclosed DE4205819A an anhydrous composition for the production of anti-corrosive coatings on metal surfaces based on silarium compounds and compounds of tetravalent titanium or zirconium.

EP1002143A discloses a process for the alkaline passivation of galvanized and alloy-galvanized steel surfaces as well as aluminum and its alloys in belt plants. This passivation with an aqueous solution results in a corrosion protection layer, which can serve as the basis for subsequent painting.

These publications mainly relate in particular to the passivation of aluminum and zinc containing surfaces of hot-dip galvanized sheet and other hot-dip galvanized steel parts for use in the automotive industry. However, a practical method for chromate-free passivation of tinplate, which provides satisfactory results, is not yet known.

EP1270764A discloses a surface-treated tinplate comprising an alloy layer on a surface of a steel sheet, a tin layer coated on the alloy layer so that the alloy layer is exposed on an area of 3.0% or more and having thereon a film including P and Si a coating weight of 0.5 to 100 mg / m ² or 250 mg / m ² applied to the exposed alloy layer and the tin layer.

Chromium-free aftertreatment agents for tinplate are in the US 2009/0155621 A1 and the publications cited therein.

EP1767665A describes a method for passivating a tinplate, in which an aqueous solution of a surface-active substance is sprayed onto a steel strip which is moved at a belt speed between 200 and 600 m / min and coated with tin. Suitable surface-active substances include polymethylsiloxanes having polyether side chains and acidic polyethers.

Disadvantages of the prior art

When using coated steel sheet for the production of food containers (cans) are compared to the requirements for the above materials, which are intended for use in the automotive industry, set other requirements for the oxidation resistance and thus the passivation of the coated metal surface. In particular, the passivation here must prevent excessive growth of the tin oxide layer during storage of the coated steel sheet or the food containers produced therefrom until painting and beyond until consumption of the preserve. Furthermore, the passivation should prevent discoloration of the coated metal surface. Such discolorations occur, for example, in the sterilization of cans with sulfur-containing contents, because the sulfur reacts with the tin of the coated sheet steel surface, if it is not sufficiently passivated. The matt discoloration (marbling) or gold coloration of the surface of the packaging may give the consumer the impression that the product is spoiled. The reaction with sulfur can also lead to paint adhesion problems, which can be avoided by passivation of the coated steel sheet. The passivation must also ensure the resistance of the painted metal container after filling with food against acids contained in the food, such. B. mercapto-aminocarboxylic acid anions, such as cysteine and methionine. Such acid anions in the product can cause delamination of the inner coating of the container in case of insufficient passivation.

In the conventional production of tinplate in strip-tinning systems, the cold-rolled fine or ultra-fine sheet is first melted by heating to temperatures above the tin melting point after tinning and then quenched in a water bath. Passivation is then carried out by treating the tinned steel sheet with a chromate solution and finally rinsing with demineralized water and drying it thermally. This is followed by electrostatic lubrication with dioctyl sebacate (DOS) or acetyltributyl citrate (ATBC). The chromate adsorbed on the tinplate surface is converted by reaction with the = Sn = O and = Sn-OH groups the tin surface to Cr ³⁺ and in electrochemical cathodic passivation also partly reduced to chromium metal. The Cr ³⁺ precipitates as Cr ³⁺ hydroxide. The passivation layer contains no more Cr ⁶⁺ ions after rinsing and drying the tinplate ^surface .

Object of the invention

Based on this, the object of the invention is to provide a process for the chromium-free passivation of the surface of steel strips coated with a tin coating, which are moved at a belt speed through a coating system, which enables efficient passivation of the steel belt surface even at high belt speeds , In addition, at the same time an improved paint adhesion and resistance to acids in foods, especially against sulfur-containing amino acids, can be achieved.

Solution to the problem of the invention

These objects are achieved with a method having the features of claim 1 and with a tin-plated steel sheet or strip having the features of claim 15. Preferred embodiments are defined in the subclaims.

In the method according to the invention, after the melting and quenching of the tin-plated steel strip and before the treatment with a chromium-free aftertreatment agent, an anodic oxidation of the tin surface is provided. The invention is based on the recognition that the passivation of the tinned surface of the steel strip by aftertreatment with a chromium-free aftertreatment agent alone is not sufficient to protect the surface over the entire surface and permanently against corrosion and discoloration (marbling). In particular, it has been found that chromium-free aftertreatment agents do not protect the tin-plated steel strip surface from reaction with sulfur. It has now surprisingly been found that the resistance of the tinned steel strip surface against corrosion and reaction with sulfur increases considerably can be, if prior to the post-treatment with a chromium-free aftertreatment agent initially carried out an inerting of the tinned steel strip surface by an anodic oxidation. The anodic oxidation produces an oxide layer with a layer thickness in the nm range on the tinned steel strip surface. The oxide layer is essentially a layer of tetravalent tin oxide (SnO ₂ ), which is substantially more inert than divalent tin oxide (SnO). If, according to the invention, a thin surface layer of a chromium-free aftertreatment agent is applied to this oxide layer, the surface of the tinned steel strip is fully and effectively protected against corrosion and against reaction with sulfur.

The method according to the invention will be described in more detail below with reference to an exemplary embodiment:

Step 1

In the first step of the process according to the invention, an electrochemical tinning of a cold-rolled steel strip (fine or ultra-fine plate) takes place in a strip-tinning plant. The steel strip is thereby moved through an electrolytic bath at a belt speed, which is usually in the range from 200 m / min to 750 m / min, and electrolytically coated with tin. Subsequently, the steel strip is conductively or inductively (or conductively and inductively) heated to temperatures above the tin melting point (232 ° C) to melt the tin coating. Thereafter, the moving steel strip is quenched in a water bath. With this fresh surface, the tinned steel strip reaches the second step of the process, namely the anodic oxidation of the tin surface.

step 2

In the second step of the process according to the invention, anodic oxidation takes place in soda solution, ie in sodium carbonate solution. The tinned steel strip is thereby moved further at the belt speed and connected as an anode in the soda-electrolyte bath polarized. The electrolyte used is an aqueous soda solution. The concentration of sodium carbonate in the soda solution is preferably 1 wt .-% to 10 wt .-%, preferably 2 wt .-% to 8 wt .-%, preferably 3 wt .-% to 7 wt .-%, especially 4 Wt .-% to 6 wt .-%, in particular about 5 wt .-%.

The device for electrolytic anodic oxidation expediently comprises an electrolytic immersion bath with a vertical tank. In the vicinity of the bottom, a deflection roller is arranged within the vertical tank, via which the tinned steel strip is deflected. The vertical tank is filled with the electrolyte. A potential is applied between the tin-plated steel strip and the counter-electrode (for example, a steel cathode) in the vertical tank. The charge amount Q is suitably between 0.2 C and 2 C, preferably between 0.2 C and 0.6 C at a current density of 1-3 A / dm ^second

The anodization time corresponds to the residence time of the tinned steel strip in the electrochemical oxidation bath (electrolyte bath). This is predetermined by the length of the electrolyte bath or its fill level as well as the anode length and the belt speed and is advantageously in the range of 0.1 s to 1 s, in particular between 0.1 s and 0.7 s, preferably in the typical belt speeds Range from 0.15s to 0.5s, and ideally 0.2s. The anodization time, depending on the belt speed, can be set to the values suitable according to the invention via the fill level.

The distance between the steel strip and the counter electrode in the electrolyte bath is set by the system. It is, for example, in the range of 3 to 15 cm, preferably in the range of 5 to 10 cm and in particular by 10 cm.

The temperature of the electrochemical oxidation bath is preferably in the range of 30 to 60 ° C, more preferably in the range of 35 to 50 ° C, and especially around 45 ° C.

The current density is set in the range of 1.0 to 3 A / dm ² , preferably 1.3 to 2.8 A / dm ² , more preferably 2 to 2.6 A / dm ² , more preferably 2.4 A / dm ² , The total amount of charge moves in the range between 0.2 C and 0.6 C and is preferably, for example, 0.48 C. The corresponding charge densities (with respect to the area of the treated tape) are in the range of 0.2 C / dm ² to 0.6 C / dm ² .

step 3

In the third step of the process, thorough rinsing of the tinned and oxidized steel strip with distilled or completely desalted water followed by drying, e.g. can be done with hot air. For this purpose, however, other drying measures are suitable, such as drying with water-absorbing solvents and then drying with a cold or hot air blower, which also the use of hot air is preferred for drying with air-convection drying equipment such as IR radiation body, inductive heating or resistance heating, or drying only with a cold or hot air blower, preferably a hot air blower.

Step 4

In the fourth step of the process, the tinned and oxidized steel strip surface is coated with a post-treatment agent.

For this purpose, a solution of the aftertreatment agent, preferably a solution with water or an organic solvent, or a ready-to-use preparation of the aftertreatment agent is sprayed onto the steel belt moving at the belt speed. Expediently, 1.5 to 10% strength aqueous solutions of the aftertreatment agent have been found. Preferably, the solution of the aftertreatment agent is then squeezed off by means of squeezing rollers and dried. After squeezing and drying, only a thin film of the aftertreatment agent still remains on the surface of the coated metal strip, wherein the support of this thin film is usually between 2 and 30 mg / m ² .

The aftertreatment agent is, for example, sprayed on pipes, which are arranged at a distance from the coated metal strip surface and transversely to the strip running direction, and Have holes or nozzles through which passes the aftertreatment agent on the coated steel strip surface. At least one tube with such bores is preferably arranged on each side of the steel strip in order to spray or spray both sides of the metal strip with the aftertreatment agent. Preferably, the distance of the tubes to the tinned and anodized steel strip is adjusted and the position of the bores or nozzles with respect to the direction of movement of the steel strip is selected so that the exiting liquid treatment agent perpendicular to the steel strip surface or at least within an angular range of + - 45 °, preferably impinge on the surface of the steel strip within an angular range of + -15 ° around the normal (vertical).

As an alternative to spraying the aftertreatment agent on the surface of the tinned steel strip and an application in a dipping process is possible.

To squeeze the sprayed-on treatment agent, two pairs of squeezing rollers are expediently arranged in the strip running direction behind the tubes. The distance of the first pair of squeezing rollers to the tubes in the direction of travel is approximately between 20 and 100 cm. After squeezing, only a few molecular layers of the aftertreatment solution remain on the tinned steel belt surface, possibly only a single-molecule solution layer.

The squeezed from the squeezing rollers solution collects in a storage tank, from where the excess post-treatment solution is fed via a pump, if necessary, a treatment and reuse.

As the post-treatment agent, the agents defined below can be used. Representative of these is the application of a Ti / Zr-containing post-treatment agent is described. As Ti / Zr containing the post-treatment agent available from Henkel KGaA under the trade mark ^® 1456 Granodine substance is, for example, used. This is prepared as a solution with a dry coverage in the range of 0.5 to 2 mg Ti / m ² , more preferably 0.8 to 1.5 mg Ti / m ² , in particular by 1 mg Ti / m ² , on the tinned and oxidized steel strip surface applied.

Step 5

The fifth step is again a drying step, wherein the drying temperature (strip temperature) in the range of 30 to 95 ° C and preferably between 35 and 60 ° C. The drying time is adapted to the belt speed. In this case, the drying devices mentioned in step 3 can be used.

The method described, a tin-plated steel sheet is achieved with a layer structure, which is composed as follows: At the bottom is as a support a cold-rolled steel sheet, in particular a fine or Feinstblech with a thickness of 0.5 mm to 3 mm (sheet) or less than 0.5 mm (fine sheet). On the steel plate follows as the next layer, for example. Electrodeposited tin layer. The tin coating is usually 0.1 to 11.2 g / m ² , but in individual cases may be less than 0.1 g / m ² or more than 11.2 g / m ² . Any alloy layers of support material and tin are neglected here as separate intermediate layers. On the tin layer then follows the oxide layer produced by the anodic oxidation with a thickness of a few nm, which consists essentially of tetravalent tin oxide. The thickness of the tin oxide layer is estimated to be in the range of 2 to 10 nm. The surface layer is followed by the aftertreatment agent layer which has been deposited on the thin oxide layer by the post-treatment and subsequent drying. The application of the post-treatment agent in the dry state (dry coating) is expediently between 2 and 30 mg / m ² .

The sheet metal produced and treated according to the invention is either cut up in the form of metal sheets or rolled up as a roll (coil). The end user, for example, the manufacturer of tin cans, the sheet is then usually provided with a coat of paint, for example. With a tin can or an epoxy paint. By deep-drawing the painted sheet is then processed into moldings, for example to tin cans. The layer structure resulting from the treatment according to the invention contributes, in comparison to known tinplate materials, to an improved paint adhesion and a reduced flaking off of the paint, for example due to the presence of mercapto-group-containing amino acids.

The substances which are suitable for use in the process according to the invention for the after-treatment of the surface of anodized tinplate must have properties such that they can adhere to the tin surface and at the same time permit wetting of the lacquer layer to be applied during the subsequent coating of the tin surface. The bond between the functional group on the anodized tin surface and the functional groups of the lacquer surface with their adhesion promoter molecules must be so strong after drying of the lacquer film that they are in the cysteine test (sterilization of the painted tinplate at 121 ° C. for 90 minutes in a solution of 3.65 g / l KH ₂ PO ₄ with 7.22 g / l Na ₂ HPO ₄ * 2H ₂ O and 1 g / l cysteine). Furthermore, the substances used for the aftertreatment should be usable without chromium and without the addition of organic solvents, or be soluble in distilled water, since the use of solubilizers would cause too high concentrations of the solvents in the exhaust air and would thus require costly cleaning systems for the removal of the solvents ,

Substances which are particularly suitable as aftertreatment agents have, for example, proved to be substances which are preferably used in practice as additives for the better dispersion of pigments in paints or for improving the wetting and / or the adhesion of paints to metal surfaces. Such agents are selected from copolymers of acrylates, polymethylsiloxanes with polyether side chains, acidic polyethers, and polymers having heterocyclic groups. But even those substances which are used as corrosion inhibitors for sheets, for example in the automotive industry, for example, Bonder or Parkerisierungsmittel, can be used advantageously. Such materials are selected from acidic, aqueous, liquid compositions containing complex metal fluoride anions with di- to tetravalent cations and polymeric materials

• a) ein organisch-modifiziertes Polysiloxan mit einem Brechungsindex von 1,456 bis 1,466 nach DIN 53491 und einer Dichte bei 20°C von 1,09-1,13 g/cm³ nach DIN 51757, [im Handel unter der Bezeichnung "EFKA 3580" erhältlich],
• b1) ein Polymer mit einer chemischen Zusammensetzung von einem sauren Polyether mit einer Dichte von 1,20-1,30 g/cm³ nach DIN 51757 und einem Säurewert von 270-310 mg KOH/g nach DIN 53402, [EFKA 8512],
• b2) ein mit Fluorcarbonresten modifiziertes Polyacrylat, neutralisiert mit Dimethylethanolamin, wobei eine wässrige Lösung mit 59 bis 61 Gew.-% Wirkstoffen bei 20°C eine Dichte von 1,04 bis 1,06 g/cm³ nach DIN 51757, einen Brechungsindex von 1,420 bis 1,440 nach DIN 53491 und einen Säurewert von 50 -70 mg KOH/g nach DIN 53402 aufweist, [EFKA 3570],
• b3) ein modifiziertes Polyacrylat, welches bei einem Anteil von 38-42 Gew.-% Wirksubstanz in Wasser eine Dichte von 1,02 bis 1,06 g/cm³ nach DIN 51757 und eine Aminzahl von 22 bis 28 mg KOH/g nach DIN 16945 aufweist, [EFKA 4560],
• c) ein Polymer das enthält:
  1. i) 0-80 Mol % von einem oder mehreren Monomeren der Formel
     
     wobei R₁, R₂, R₃ und R₄ gleich oder verschieden sein können und H oder Alkyl darstellen,
  2. ii) 0-70 Mol % von einem oder mehreren Monomeren der Formel
     
     worin R₅, R₆ und R₇ gleich oder verschieden sein können und H oder Alkyl darstellen, und R₈ Alkyl oder substituiertes Alkyl darstellt, und die Alkylgruppe R₈ durch - O- Gruppen unterbrochen sein kann,
  3. iii) 5-50 Mol % von einem oder mehreren Monomeren, enthaltend eine heterocyclische Gruppe mit mindestens einem basischen Ringstickstoffatom, oder an das bzw. an die eine derartige heterocyclische Gruppe sich nach einer Polymerisation befindet,
  4. iv) 0-10 Mol % von einem oder mehreren Monomeren, enthaltend eine oder mehrere Gruppen, die für Vernetzung oder Kupplung reaktiv sind, und
  5. v) 0-20 Mol % von einem oder mehreren Monomeren, die nicht in die vorstehenden Gruppen i) - iv) fallen, wobei die Menge der Monomere von Gruppe i) zusammen mit Monomeren, die eine Acrylatgruppe enthalten, mindestens 20 Mol % beträgt, sowie organische Salze davon, oder
• d) eine saure, wässrige, flüssige Zusammensetzung, die neben Wasser und ggf. Lösemitteln, die folgenden Komponenten enthält:
  1. (A) Fluormetallatanionen mit Titan, Zirkonium, Hafnium, Silizium, Aluminium und/oder Bor als Zentralatom; sowie gegebenenfalls ionisierbaren Wasserstoffatomen, und/oder gegebenenfalls einem oder mehreren Sauerstoffatomen;
  2. (B) ein oder mehrere zwei- bis vierwertige, insbesondere zweiwertige und/oder vierwertige Kationen von Kobalt, Magnesium, Mangan, Zink, Nickel, Zinn, Kupfer, Zirkonium, Eisen und/oder Strontium;
  3. (C) Phosphor enthaltende anorganische Oxianionen und/oder Phosphonatanionen, und
  4. (D) ein oder mehrere wasserlösliche und/oder in Wasser dispergierbare organische Polymere und/oder polymerbildende Harze.

Particularly suitable after-treatment agents for the process according to the invention, besides copolymers of acrylates, are the following substances:

• a) an organically modified polysiloxane having a refractive index of 1.456 to 1.466 according to DIN 53491 and a density at 20 ° C. of 1.09-1.13 g / cm ³ according to DIN 51757, [commercially available under the name "EFKA 3580" available],
• b1) a polymer having a chemical composition of an acidic polyether with a density of 1.20-1.30 g / cm ³ according to DIN 51757 and an acid value of 270-310 mg KOH / g according to DIN 53402, [EFKA 8512],
• b2) a fluorocarbon-modified polyacrylate neutralized with dimethylethanolamine, wherein an aqueous solution with 59 to 61 wt .-% of active ingredients at 20 ° C has a density of 1.04 to 1.06 g / cm ³ according to DIN 51757, a refractive index of 1,420 to 1,440 according to DIN 53491 and has an acid value of 50-70 mg KOH / g according to DIN 53402, [EFKA 3570],
• b3) a modified polyacrylate, which at a content of 38-42 wt .-% active ingredient in water, a density of 1.02 to 1.06 g / cm ³ according to DIN 51757 and an amine value of 22 to 28 mg KOH / g after DIN 16945, [EFKA 4560],
• c) a polymer containing:
  1. i) 0-80 mol% of one or more monomers of the formula
     
     wherein R ₁ , R ₂ , R ₃ and R _{4 may be the} same or different and represent H or alkyl,
  2. ii) 0-70 mol% of one or more monomers of the formula
     
     wherein R ₅ , R ₆ and R _{7 may be the} same or different and represent H or alkyl, and R _{8 is} alkyl or substituted alkyl, and the alkyl group R ₈ may be interrupted by -O- groups,
  3. iii) 5-50 mole% of one or more monomers containing a heterocyclic group having at least one basic ring nitrogen atom or to which such heterocyclic group is located after polymerization,
  4. iv) 0-10 mole% of one or more monomers containing one or more groups reactive for crosslinking or coupling, and
  5. v) 0-20 mol% of one or more monomers which do not fall into the above groups i) - iv), the amount of the monomers of group i) together with monomers containing an acrylate group being at least 20 mol%, and organic salts thereof, or
• d) an acidic, aqueous, liquid composition which, in addition to water and optionally solvents, contains the following components:
  1. (A) fluorometallate anions with titanium, zirconium, hafnium, silicon, aluminum and / or boron as the central atom; and optionally ionizable hydrogen atoms, and / or optionally one or more oxygen atoms;
  2. (B) one or more di- to tetravalent, especially divalent and / or tetravalent cations of cobalt, magnesium, manganese, zinc, nickel, tin, copper, zirconium, iron and / or strontium;
  3. (C) phosphorus-containing inorganic oxianions and / or phosphonate anions, and
  4. (D) one or more water-soluble and / or water-dispersible organic polymers and / or polymer-forming resins.

1. (A) Fluormetallatanionen, die jeweils bestehen aus: (i) wenigstens vier Fluoratomen und (ii) wenigstens 1 Atom eines metallischen Elements, das aus der Gruppe, bestehend aus Titan, Zirkonium, Hafnium, Silizium, Aluminium und Bor, ausgewählt ist; sowie gegebenenfalls (iii) ionisierbaren Wasserstoffatomen, und/oder gegebenenfalls (iv) einem oder mehreren Sauerstoffatomen;
2. (B) eine Menge von einem oder mehreren zwei- bis vierwertigen, insbesondere zweiwertigen und/oder vierwertigen Kation(en) von Kobalt, Magnesium, Mangan, Zink, Nickel, Zinn, Kupfer, Zirkonium, Eisen und/oder Strontium, so dass das Verhältnis der Gesamtzahl des Kations (der Kationen) zu der Anzahl der Anionen in der Komponente (A) wenigstens 1:5 beträgt, jedoch nicht größer als 3:1 ist;
3. (C) Phosphor enthaltende anorganische Oxyanionen und/oder Phosphonatanionen, und
4. (D) ein oder mehrere wasserlösliche und/oder in Wasser dispergierbare organische Polymere und/oder polymerbildende Harze, wobei die Menge dieser Komponente so ist, dass das Verhältnis des Feststoffgehalts an organischem Polymer und polymerbildendem Harz in der Zusammensetzung zu dem Feststoffgehalt der Komponente (A) im Bereich von 1:2 bis 3:1 liegt.

The substance d) is preferably an acidic, aqueous, liquid composition which, in addition to water, contains the following components:

1. (A) fluorometalate anions each consisting of: (i) at least four fluorine atoms and (ii) at least one atom of a metallic element selected from the group consisting of titanium, zirconium, hafnium, silicon, aluminum and boron, is selected; and optionally (iii) ionizable hydrogen atoms, and / or optionally (iv) one or more oxygen atoms;
2. (B) an amount of one or more di- to tetravalent, especially divalent and / or tetravalent cation (s) of cobalt, magnesium, manganese, zinc, nickel, tin, copper, zirconium, iron and / or strontium, so that Ratio of the total number of the cation (s) to the number of anions in the component (A) is at least 1: 5 but not greater than 3: 1;
3. (C) phosphorus-containing inorganic oxyanions and / or phosphonate anions, and
4. (D) one or more water-soluble and / or water-dispersible organic polymers and / or polymer-forming resins, the amount of said component being such that the ratio of the solids content of organic polymer and polymer-forming resin in the composition to the solids content of the component (A ) is in the range of 1: 2 to 3: 1.

1. (A) wenigstens 0,010 M/kg Fluormetallatanionen, wobei diese Anionen jeweils bestehen aus: (i) wenigstens vier Fluoratomen und (ii) wenigstens 1 Atom eines metallischen Elements, das aus der Gruppe ausgewählt ist, die aus Titan, Zirconium, Hafnium, Silicium, Aluminium und Bor besteht; sowie gegebenenfalls (iii) ionisierbaren Wasserstoffatomen, und/oder gegebenenfalls (iv) einem oder mehreren Sauerstoffatomen;
2. (B) eine Menge von zwei- bis vierwertigen, insbesondere einem oder mehreren zweiwertigen und/oder vierwertigen Kation(en) des Cobalts, Magnesiums, Mangans, Zinks, Nickels, Zinns, Kupfers, Zirconiums, Eisens und/oder Strontiums, so dass das Verhältnis der Gesamtzahl des Kations (der Kationen) zu der Anzahl der Anionen in der Komponente (A) wenigstens 1:5 beträgt, jedoch nicht größer als 3:1 ist;
3. (C) wenigstens 0,015 MP/kg und vorzugsweise wenigstens 0,030 Mp/kg Phosphor enthaltender anorganischer Oxianionen und/oder Phosphonatanionen, und
4. (D) wenigstens 0,10 % und vorzugsweise wenigstens 0,20 % eines wasserlöslichen (oder mehrerer wasserlöslicher) und/oder in Wasser dispergierbaren (in Wasser dispergierbarer) organischen Polymers (organischer Polymere) und/oder polymerbildenden Harzes (polymerbildender Harze), wobei die Menge dieser Komponente derartig ist, daß das Verhältnis des Feststoffgehalts des organischen Polymers (der organischen Polymere) und des polymerbildenden Harzes (der polymerbildenden Harze) in der Zusammensetzung zu dem Feststoffgehalt der Komponente (A) im Bereich von 1:2 bis 3:1 liegt.

Specifically, the substance d) is an acidic aqueous liquid composition substantially free of hexavalent chromium and / or ferricyanide for treating metal surfaces not more than 1.0% and preferably not more than 0.0002 % of both the hexavalent chromium and the ferricyanide and which otherwise contain besides water the following components:

1. (A) at least 0.010 M / kg fluorometallate anions, each of said anions consisting of: (i) at least four fluorine atoms and (ii) at least one atom of a metallic element selected from the group consisting of titanium, zirconium, hafnium, silicon , Aluminum and boron; and optionally (iii) ionizable hydrogen atoms, and / or optionally (iv) one or more oxygen atoms;
2. (B) an amount of di- to tetravalent, in particular one or more divalent and / or tetravalent cation (s) of cobalt, magnesium, manganese, zinc, nickel, tin, copper, zirconium, iron and / or strontium, so that Ratio of the total number of the cation (s) to the number of anions in the component (A) is at least 1: 5 but not greater than 3: 1;
3. (C) at least 0.015 MP / kg and preferably at least 0.030 Mp / kg phosphorus-containing inorganic oxianions and / or phosphonate anions, and
4. (D) at least 0.10% and preferably at least 0.20% of a water-soluble (or more water-dispersible) and / or water-dispersible (water-dispersible) organic polymer (s) and / or polymer-forming resin (s) where the amount of said component is such that the ratio of the solids content of the organic polymer (s) and polymer-forming resin (s) in the composition to the solids content of component (A) ranges from 1: 2 to 3: 1 lies.

Preferably, component d) comprises dihydrogen hexafluorotitanate (2-) and organic polymers. Particularly preferred is the component Granodine 1456.

welche in Patentanspruch 1 und den abhängigen Patentansprüchen der Europäischen Patentanmeldung mit der Publikationsnummer EP0319017 A2 genauer definiert ist.The polymer (D) may be a polymer compound comprising a copolymer material, wherein at least a part of the copolymer has the structure

which in claim 1 and the dependent claims of the European patent application with the publication number EP0319017 A2 is defined in more detail.

• Ein Kunststoffkolben wird mit 400 ml Propasol P (ein propoxyliertes Propan-Lösungsmittel, erhältlich von Union Carbide Corp., Danbury, Conn.) und 160 g Resin M (ein Polyvinylphenol, erhältlich von Maruzen Oil MW=5000) befüllt. Eine Aufschlämmung von 263,3 g N-Methyglucamin in 400 desionisiertem Wasser wird zugegeben und das Gemisch wird auf 60-65 °C unter Rühren erwärmt. Dann werden 100,2 ml- 37 % Formaldehyd über eine bis anderthalb Stunden zugegeben. Das Gemisch wird dann auf 90°C erwärmt und für 6 Stunden gehalten. Nach dem Kühlen wird das Gemisch mit desionisiertem Wasser auf 9,6 Gew.-% Feststoffe verdünnt. Der pH-Wert der fertigen Lösung beträgt 9,1 und die Lösung umfasst ein N-Methylglucamin-Derivat.

Such a polymer can be prepared, for example, as follows:

• A plastic flask is charged with 400 ml of Propasol P (a propoxylated propane solvent, available from Union Carbide Corp., Danbury, Conn.) And 160 grams of Resin M (a polyvinyl phenol, available from Maruzen Oil MW = 5000). A slurry of 263.3 g of N-methylglucamine in 400 ml of deionized water is added and the mixture is heated to 60-65 ° C with stirring. Then 100.2 ml - 37% Formaldehyde added over one to one and a half hours. The mixture is then heated to 90 ° C and held for 6 hours. After cooling, the mixture is diluted with deionized water to 9.6 wt% solids. The pH of the final solution is 9.1 and the solution comprises an N-methylglucamine derivative.

Also suitable are the polyphenol derivatives according to the patent claim 1 and the dependent claims of the European patent application with the publication number EP 0 319 016 A2 :

• 80 g eines Harzes obiger Formel mit einem mittleren Molekulargewicht von etwa 2 400, worin R₁, R₁₃, R₁₄ und W₂ H sind, R₂ -CH₃ ist und Y₂ ein Alkylamin-Rest oder ein Alkylammonium-Rest ist (bezogen auf die in EP 0 319 016 A2 angegebene Formel I und deren Definitionen), werden langsam in 160 ml Propasol P (einem propoxylierten Propanol-Lösungsmittel, erhalten von Union Carbide Corp., Danbury, Connecticut) in einem 1 Liter Kunststoff-Kolben unter Benutzung eines Hochgeschwindigkeits-Mischers gelöst. Der Kunststoff-Kolben ist mit einem Blattrührer, einem Rückflusskühler und einer Stickstoff-Spülung ausgerüstet. Zu der Harz-Lösung werden dann 53,5 g 2-(Methylamino)ethanol und 160 ml entionisiertes Wasser gegeben. Es wird begonnen, vorsichtig auf 60°C zu erwärmen. Wenn 60°C erreicht sind, wird mit der Zugabe von 50 ml 37-% Formaldehyd in Wasser begonnen, und diese Zugabe wird während einer Zeitspanne von 1 h fortgesetzt. Weitere 25 ml Propasol P werden zugesetzt, und die Reaktionsmischung wird 1,5 h auf 60°C gehalten. Die Temperatur wird auf 80 °C erhöht und dort 1,75 h gehalten. Man lässt die Reaktionsmischung sich auf Raumtemperatur abkühlen, und 21,8 g 75-% H₃PO₄ und danach 960 ml entionisiertes Wasser werden hinzugefügt. Gegebenenfalls wird ein Aminoxid, das keinen zusätzlichen Schritt der Neutralisation benötigt, durch Hinzufügen von 0,75 Mol 30-% H₂O₂ (85 g) zu der Reaktionsmischung gebildet. Man lässt die Reaktionsmischung über Nacht rühren und verdünnt sie dann mit 960 ml entionisiertem Wasser. Das Ergebnis dieses wahlweise durchzuführenden Schrittes ist ein wasserlösliches Aminoxid-Harz, das zur Wasser-Stabilität keine Neutralisation erfordert.

Such a polymer can be prepared, for example, as follows:

• 80 g of a resin of the above formula having an average molecular weight of about 2,400, wherein R ₁ , R ₁₃ , R ₁₄ and W _{2 are} H, R _{2 is} -CH ₃ and Y _{2 is} an alkylamine radical or an alkylammonium radical ( based on the in EP 0 319 016 A2 given formula I and their definitions) are slowly dissolved in 160 ml of Propasol P (a propoxylated propanol solvent, obtained from Union Carbide Corp., Danbury, Connecticut) in a 1 liter plastic flask using a high speed mixer. The plastic flask is equipped with a paddle stirrer, a reflux condenser and a nitrogen purge. To the resin solution is then added 53.5 g of 2- (methylamino) ethanol and 160 ml of deionized water. It is started to warm gently to 60 ° C. When 60 ° C is reached, the addition of 50 ml of 37% formaldehyde in water is begun, and this addition is continued for a period of one hour. Another 25 ml of Propasol P are added and the reaction mixture is held at 60 ° C for 1.5 hours. The temperature is raised to 80 ° C and held there for 1.75 hours. The reaction mixture is allowed to cool to room temperature and 21.8 g of 75% H ₃ PO ₄ and then 960 ml of deionized water are added. Optionally, an amine oxide which does not require an additional step of neutralization is formed by adding 0.75 moles of 30% H ₂ O ₂ (85 g) to the reaction mixture. The reaction mixture is allowed to stir overnight and then diluted with 960 ml of deionized water. The result of this optional step is a water-soluble amine oxide resin which does not require neutralization for water stability.

Suitable treatment agent with the complexed transition metals, for example, products in the Granodine ^®, which represent an aqueous solution containing the complexed transition metals (Ti, Mn, Zr) and optionally a silane. Particularly suitable titanium-containing and / or zirconium aftertreatment agents have shown such products in the Granodine ^® (manufacturer: Henkel) or Gardobond ^® (manufacturer: Chemetall), in particular the products "Granodine ^® 1456" and "Gardobond ^® X 4707". These titanium-containing and zirconium-containing products are expediently metered as aftertreatment agent for the process according to the invention such that after squeezing and drying a titanium coating (dry coating) of 0.5 mg / m ² to 2 mg / m ² and in particular of about 1.0 mg / m ^{2 is present} on the surface of the treated tinplate. For this purpose, typically 1.5 to 10% aqueous solutions of these aftertreatment agents are used, wherein the titanium content in the aqueous solution is preferably between 0.2 and 1.2 g / l and more preferably between 0.2 and 0.5 g / I lies.

Components (a) to (c) were developed by EFKA Chemicals and EFKA Additives, respectively, and are currently supplied by BASF SE. The products are in the publications US5688858A . EP0311157 A1 (Page 12, line 45 to page 13, line 36, as well as the examples), US5399294A . EP0438836 A1 (Column 10, lines 42 to 57, as well as the examples), US5882393A . WO97 / 26984 A1 (Page 20, lines 4 to 20, as well as the examples), US2004063828A . WO02 / 057004 A1 (Page 11, lines 1 to 6, as well as the examples), US2004236007A . WO03 / 033603 A1 (Page 20, lines 1 to 23, as well as the examples), US2009234062A . WO2004 / 045755 A2 (Page 21, lines 2 to 13, as well as the Examples), US2007293692A such as WO2005 / 085261 A1 (Page 14, lines 1 to 25 and examples), in particular in the independent claims cited therein.

The following products from BASF SE are preferred: EFKA 3570, EFKA 3580, EFKA 4560 and EFKA 8512. Particular preference is given to EFKA 4560.

For the post-treatment agent, acrylate-containing agents having N-heterocyclic groups have been found to be particularly suitable, e.g. EFKA 4560. These correspond to the components (c) defined above.

They can be made, for example, as follows

In a reaction flask with reflux condenser suitable for polymerizations, 2.84 g of vinyltoluene, 4.55 g of isobutyl methacrylate, 7.36 g of ethylhexyl acrylate, 5.20 g of hydroxyethyl methacrylate, 1.80 g of polyethylene glycol monomethacrylate are dissolved in 9.86 g of xylene and 4.93 g of methoxypropyl acetate having a molecular weight of about 400 and 0.44 g of di-tertiary-butyl peroxide dissolved. The polymerization was carried out at the boiling point of the mixture while stirring and introducing an inert gas. At the end of the polymerization, 9.79 g of isophorone diisocyanate were dissolved in 16.58 g of isobutyl acetate and 16.58 g of methoxypropyl acetate, and the remaining free NCO groups were then reacted with 3.60 g of polyethylene glycol monomethacrylate having a molecular weight of about 400 and 4.51 g 1- (3-aminopropyl) imidazole reacted.

The solids content was then adjusted to 40% by weight with butyl acetate.

In a manner similar to above, 3.54 g of vinyl toluene, 5.69 g of isobornyl methacrylate, 9.20 g of 2-ethylhexyl methacrylate, 7.15 g of hydroxyethyl methacrylate, and 1.28 g of di-tertiary-butyl peroxide dissolved in 11.94 g of xylene and 5.97 g of methoxypropyl acetate, polymerized.

Then, 12.23 g of isophorone diisocyanate dissolved in 20.36 g of butyl acetate and 20.36 g of methoxypropyl acetate were added. The remaining free NCO groups were then reacted with 4.50 g of polyethylene glycol monomethacrylate having a molecular weight of about 400 and 3.78 g of 3-amino-1,2,4-triazole in 11.34 g of N-methylpyrrolidone.

The solids content was then adjusted to 40% by weight with butyl acetate.

These substances are sprayed undiluted or as an aqueous solution onto the tinned steel strip according to the above-described method of the invention and optionally subsequently squeezed off and dried. As order quantity for eg the substance EFKA 4560, dry runs in the range of 2 to 15 mg / m ² and preferably between 2 and 10 mg / m ^{2 are} suitable.

With the aftertreatment agent (s), the (further) tin oxide growth on the coated metal strip surface can be greatly reduced during its storage until it is painted. At the same time, in the case of the treatment according to the invention of the anodically oxidized, tinned steel strip surface with these aftertreatment agents, the paint adhesion is improved. The tinplate surfaces treated according to the invention have proven to be very easy to paint.

As a result of the inventive treatment of tinplate with an anodic oxidation and the order of the chromium-free aftertreatment agent has been shown that sulfur-containing substances that occur in food, for example, derived from the amino acids cysteine or methionine, no longer through diffusion through the later applied paint layer and the passivation according to the invention can reach the tin surfaces and there cause unsightly marbling (yellowing or browning), which are essentially due to the formation of tin sulfide, and which in extreme cases lead to a deterioration of the paint adhesion to the tinplate or even to a detachment of the paint application could.

Some of the tinplate samples treated according to the invention have a markedly reduced sliding friction compared to untreated tinplate, and even lower sliding friction values could be determined for individual substances than with conventional treatment of the tinplate with DOS.

From an overall view of the results of comparative experiments, it can be deduced that the process according to the invention for passivating the surface of tinplate by anodic oxidation and coating with the aftertreatment agents used according to the invention gives the best results in terms of oxidation resistance and marbling resistance (sulfide barrier effect) and sliding friction become. The results are comparable to the quality of the known from the prior art passivation of tinplate with chromium-containing aftertreatment agents.

The substances "EFKA 3580", "EFKA 4560", "EFKA 8512" and "EFKA 3570" give very good results as aftertreatment agent in terms of properties low sliding friction, oxidation resistance (low tin oxide growth) and marbling resistance (sulfide barrier effect). As a preferred aftertreatment has "EFKA 4560" out in this regard. With regard to the Marmorierungsbeständigkeit and the paint adhesion, the titanium-containing post-treating agent of the product lines show Granodine ^® (especially "Granodine ^® 1456") and Gardobond ^® (especially Gardobond X ^® 4707) very advantageous results. However, other chromium-free aftertreatment agents, some of which are already known from the prior art, are also suitable for carrying out the process according to the invention. The method according to the invention can be applied both to tinplate with a melted tin layer and to tinplate, in which the tin layer has not been melted.

Claims (15)

1. Method for passivation of the surface of tinned steel strip which is moved through a coating installation at a strip speed of at least 200 m/min, wherein after the tinning of the steel strip first the surface is anodically oxidised in order to form an oxide layer which essentially consists of tetravalent tin oxide (SnO₂), and then a liquid solution of a chromium-free after-treatment agent is applied to the oxide layer, wherein the after-treatment agent is selected from copolymers of acrylates, polymethyl siloxanes with polyether side chains, acid polyethers, polymers with heterocyclic groups and acid, aqueous,liquid compounds which contain complex metal fluoride anions with divalent to tetravalent cations and polymeric substances.
2. Method according to claim 1, wherein the anodic oxidation is carried out with a basic electrolyte and with a current density of from 1.0 A/dm² to 3 A/dm² bypassing the tinned steel strip through an electrolysis bath.
3. Method according to claim 2, wherein the basic electrolyte is selected from alkali metal or alkaline earth metal hydroxide or carbonate, basic alkali metal phosphate and basic organic alkali metal or alkaline earth metal salt.
4. Method according to claim 2 or 3, wherein the electrolyte contains sodium carbonate.
5. Method according to claim 2, characterised in that the electrolysis bath is adjusted so that a charge of at least 0.2 C is obtained.
6. Method according to one of the preceding claims, characterised in that the after-treatment agent contains titanium and/or zirconium.
7. Method according to one of the preceding claims, wherein after the anodic oxidation an aqueous solution of the after-treatment agent or a ready to use solution of the after-treatment agent is applied by passage through a bath containing the after-treatment agent.
8. Method according to one of the preceding claims, characterised in that the after-treatment agent is sprayed on by means of at least one pipe which is arranged a distance from the coated surface of the metal strip and exhibits at least one bore or nozzle through which the after-treatment agent is sprayed on to the or each coated surface of the steel strip.
9. Method according to one of the preceding claims, characterised in that the solution of the after-treatment agent is applied on both sides of the steel strip.
10. Method according to one of claims 8 or 9, characterised in that the after-treatment agent is sprayed on to the tinned steel strip surface(s) in the form of jets of liquid, wherein the jets of liquid impinge on the surface at an angle ranging from +45° to -45° with respect to the normal.
11. Method according to one of the preceding claims, characterised in that after the application on the tinned and oxidised surface of the steel strip, the solution of the after-treatment agent is squeezed off by means of squeezing rollers and after the after-treatment agent has been squeezed off the tinned steel strip is dried.
12. Method according to claim 11, characterised in that after the squeezing off of the after-treatment agent and the drying, a thin film of the after-treatment agent with a coatingof between 2 mg/m² and 30 mg/m² is present on the surface of the tinned steel strip.
13. Method according to claim 11, characterised in that the after-treatment agent contains titanium and in that after the squeezing off of the titanium-containing after-treatment agent and after the drying, a thin film of the after-treatment agent with a titanium coatingof between 0.5 mg/m² and 2 mg/m² is present on the surface of the tinned steel strip.
14. Method according to one of the preceding claims, characterised in that the anodic oxidation of the tinned surface of the steel strip is carried out within an anodisation time of from 0.1 to 1.0 seconds and preferably within an anodisation time of between 0.2 and 0.7 seconds.
15. Tinned steel strip or sheet with a carrier layer composed of a fine or ultra-fine sheet of steel, a layer of tin deposited thereon and a surface layer of a chromium-free after-treatment agent, characterised in that between the layer of tin and the surface layer of the after-treatment agent is formed an oxide layer which essentially consists of tetravalent tin oxide (SnO₂) and in that the after-treatment agent is selected from copolymers of acrylates, polymethyl siloxanes with polyether side chains, acid polyethers, polymers with hetrocyclic groups and acid, aqueous, liquid compounds which contain complex metal fluoride anions with divalent to tetravalent cations and polymeric substances.