DE102013107506A1 - Method for passivation of band-shaped black plate - Google Patents

Abstract

The invention relates to a process for the passivation of strip-shaped black plate, comprising the following steps: electrochemical treatment of the black plate by passing the black plate through an electrolyte to form an inert steel surface, rinsing the black plate, applying an aqueous chromium-free treatment solution to at least one surface of the black plate for the formation of a corrosion-protecting conversion layer and an adhesive layer for paints and organic coating materials. The black sheets treated according to the invention are distinguished by high corrosion resistance and have good adhesion to paints and organic coatings and are therefore very suitable as substitutes for tin-free steel sheet (TFS or ECCS) and tinplate for the production of packaging, in particular cans. In contrast to the conventional production and passivation of tin-free sheet steel and tinplate no environmentally and health hazardous chromium-VI is used in the process according to the invention.

Description

The invention relates to a method for the passivation of strip-shaped black sheet, wherein in an initial step by an electrochemical treatment of the black plate an inert layer is formed on the black plate surface and in a further step, an aqueous chromium-free treatment solution on at least one surface of the black plate to form a protective against corrosion Conversion layer is applied, which also forms an adhesive layer for paints and organic coating materials. Passivation is understood here to mean the targeted generation of a protective layer (here: conversion layer) on the black sheet, which prevents or at least greatly slows the corrosion of the black sheet. The invention further relates to the use of black plates treated according to the invention as packaging steel.

In order to protect metallic surfaces against corrosion, methods are known in which the metallic surface is provided with a coating of another, usually less noble metal (such as, for example, zinc and chromium). So it is z. B. known steel sheets with zinc or chromium or with tin (which, however, is noble compared to steel) to coat. For the production of packaging, in particular in the food industry, for example, very extensively tinned Feinstbleche (tinplate) are used. Tinplates are characterized by a very good corrosion resistance and a good forming behavior and their weldability and are therefore very well suited for the production of packaging such. B. beverage cans.

In order also to protect the metallic coating, for example the tin coating in tinplate, against corrosion and to produce a good primer for coatings and plastic coatings, conversion coatings are frequently applied to the surface of the metallic coating.

Conversion layers are non-metallic, usually inorganic, very thin layers on a metal surface, which are generally produced by chemical reaction of an aqueous treatment solution with the metallic substrate. Conversion coatings ensure a very effective corrosion protection, in particular with fine metal sheets, a good primer for coatings and plastics and they reduce surface friction and abrasion.

Depending on the substrate, a distinction is made between iron, zinc or manganese phosphating, electrolytic phosphating or chromate, oxalate and anodization processes. Chromium-containing conversion layers have proven to be very effective corrosion protection. In chromating, the metallic surface is treated with an acidic solution containing chromium (VI) ions, whereby chromium (VI) is reduced to chromium (III). The treatment forms a chromium-containing conversion layer which protects against corrosion on the metal surface.

However, chromium (VI) compounds are acutely toxic and carcinogenic. For automotive and home appliance applications, the passivation of metal surfaces containing chromium (VI) -containing substances has already been banned in the EU. For this reason, chromium-free conversion layers have been developed in the prior art. So are, for example, from the WO 97/40208-A and the EP 2532769 A1 Method for producing chromium-free conversion layers on zinc or aluminum surfaces known. In the WO 2008/119675 Furthermore, treatment solutions for the production of chromium-free conversion layers are described which contain oxo cations and halogen complex ions, which lead to colorless and slightly iridescent conversion layers.

Tinplate has excellent properties as a food packaging material and has been manufactured and processed for many decades for this purpose. However, tin, which is the anticorrosion coating on tinplate, has become a relatively valuable material due to the global shortage of resources. As an alternative to tinplate, especially for use as packaging steel of the prior art, electrolytically plated chromium plated steel sheets are known as Tin Free Steel (TFS) or Electrolytic Chromium Coated Steel (ECCS) , On the one hand, these tin-free steel sheets are distinguished by a good adhesion to paints or organic protective coatings (for example of PP or PET), but on the other hand have considerable advantages in carrying out the coating process because of the toxic and health-endangering properties of the chromium-VI-containing materials used for coating Disadvantages.

The object of the present invention is therefore to provide a chromium-free packaging steel, which is suitable as a substitute for tin-free steel sheet (TFS or ECCS) and as a replacement for tinplate and in particular both in terms of corrosion resistance and with respect to the adhesion for paints or organic coatings should be with tinplate or tin-free steel.

This object is achieved by a method for passivation of black belt-shaped sheet having the features of claim 1. According to this method, an uncoated black plate is used in strip form and its surface rendered inert in a first step by an electrochemical treatment, then rinsed with water and finally in a another step coated with a corrosion-stable conversion coating by applying to at least one surface of the black plate an aqueous chromium-free treatment solution.

Further particular embodiments of the method are defined in the dependent claims.

• • Festigkeit: 300–1000 MPa
• • Bruchdehnung: 1–40%
• • Dicke: 0,05–0,49 mm
• • Oberflächen-Rauheit: 0,1–1 μm.

Cold-rolled, annealed and tempered steel strip made of an unalloyed steel with a carbon content of 20-1,000 ppm is preferably used. Suitably, the steel strip (black plate) has the following properties:

• • Strength: 300-1000 MPa
• • Elongation at break: 1-40%
• • Thickness: 0.05-0.49 mm
• • Surface roughness: 0.1-1 μm.

The steel may, for example, be a ferritic steel or else a multiphase steel which has a plurality of structural constituents, in particular ferrite, martensite, bainite and / or retained austenite. Such multiphase steels are characterized by a high strength of more than 500 MPa with simultaneously good elongation at break of more than 10%. With regard to the intended use of the invention treated black plate as a packaging steel are preferably in the DIN EN 10202: 2001: "Cold-rolled sheet-metal products (electrolytically tinned and chromium-plated)" defined grades of the steel sheet met. Among other things, this standard defines the analysis and mechanical characteristics of the steel. The grades are in particular between TS230 (soft bonnet grade, yield strength 230 MPa) to TH620 (DO, 620 MPa).

To carry out the process according to the invention, the black plate in strip form is moved at a belt speed of preferably more than 200 m / min and up to 750 m / min. First, a step of forming an inert layer on the surface of the black sheet by an electrochemical treatment. To prepare the electrochemical treatment, the moving black plate strip is first cleaned in a possibly required pretreatment step and in particular degreased, then rinsed, pickled and rinsed again. This may be necessary because the cold-rolled and recrystallization-annealed black sheet is usually tempered after recrystallization annealing, for example, when wet-rolling with a water-oil suspension or dry-soaking the blackplate surfaces by oil, iron abrasion, soaps and others Contaminants are contaminated. This contamination is eliminated by the (optional) pretreatment step.

For this purpose, the black plate is passed into a cleaning tank with an alkaline sodium or potassium hydroxide solution. The concentration of the alkaline degreasing agent is preferably between 20 and 100 g / l at bath temperatures of 20-70 ° C. A degreasing of the black plate is expediently carried out in two steps, wherein in a first step a dipping method and in the second step an electrolytic method with current densities of 2 to 30 A / dm ^{2 is} performed. After degreasing, each band side of the black plate is rinsed, for example, by a triple cascade rinsing with 10-30 m ³ / h of water. Removal of oxide residues may, if necessary, be accomplished by passing the blackplate tape into further cleansing tanks having a salt or sulfuric acid pickle at a concentration of, for example, 10 to 120 g / l in two consecutive dives, followed by a dive with a dive. The temperatures of the pickling solution and the rinsing water are typically between 20 and 60 ° C.

After pretreatment, a homogeneous, dense, inert steel surface is produced by electrochemical treatment by passing the black metal strip through an electrolyte. The electrolyte is preferably alkaline. The electrochemical, preferably alkaline treatment of the black plate is used for inerting and for equalizing the surface properties of the steel strip before applying the conversion coating.

In the electrochemical treatment step, the black plate belt is passed through the belt speed through an electrolytic bath while being connected as an anode at a preferred current densities of 2-30 A / dm ² . The electrolyte is, for example, a sodium hydroxide bath (NaOH conc. 20-100 g / l). The bath temperatures of the electrolysis bath are suitably maintained between 20 and 80 ° C.

After the electrochemical treatment, the black plate is rinsed with water. The rinsing can be done by immersing the tape in a water tank or by spraying with water. Deionized water, osmosis water or distilled water at temperatures of 20-60 ° C is preferably used for this purpose. After rinsing, the black plate is dried.

Finally, in a final step, a conversion layer is applied to at least one surface of the black plate by applying an aqueous chromium-free treatment solution to the surface of the black plate previously rendered inert in the electrochemical treatment.

The conversion coating is expediently applied in a no-rinse method, that is to say rinsing after generation of the conversion layer is omitted. The aqueous chromium-free treatment solution which forms the conversion coating is applied, for example, to the surface of the black plate with a coating device which comprises a roller coater, a rotary sprayer or spray nozzles.

For application of the aqueous treatment solution, it is preferable to use an application device with a rotary sprayer. Before application of the treatment solution, the surface of the black plate to which the conversion layer is to be applied should be as clean and dry as possible. Therefore, at least the to be coated with the conversion layer surface of the black plate with a drying device, for. B. with an Air Knife, dried. With this Air-Knife a laminar hot air flow is inflated onto the surface of the moving belt, so that disturbing foreign particles are blown off the steel belt surface and the steel belt surface is dried.

The rotary sprayer has a plurality of spray rotors juxtaposed transversely to the belt running direction to which the aqueous treatment solution is supplied and which are rotated by a drive to spray the aqueous treatment solution on the or each surface of the belt in the form of a fine spray jet due to centrifugal force Form wet film of the aqueous solution. After application of the wet film of the aqueous treatment solution, this is made uniform by means of powered smoothing rollers on the surface of the black plate. The smoothing rollers are expediently arranged with respect to the black plate surface (s) such that they exert only little pressure on the wet film of the aqueous treatment solution and squeeze no or at most a minimal portion of the applied treatment solution from the surface. The amount of treatment solution sprayed with the rotary sprayer is adjusted accordingly so that there is no excess on the blackplate surface. This eliminates the otherwise necessary disposal or treatment of the excess portion of the treatment solution. After the wetted wet film is evened out, it is dried so that a dry coating of the treatment substance remains on the treated black sheet surface (s). The dry coating of the treatment solution after drying is expediently between 1 and 50 mg / m ² and is preferably in the range from 10 to 30 mg / m ² . The amount of the aqueous treatment solution fed to the spray rotors of the rotary sprayer per unit time is expediently adapted to the belt speed. This can ensure that only the exact amount of fresh treatment solution is used in the appropriate concentration with the rotary sprayer as a wet film on the black plate tape is applied. Thus, for example, a constant circulation of the wet film in the range of 2 ml / m ² to 8 ml / m ² and preferably of about 5 ml / m ² per band side can be set independently of the belt speed.

After applying the wet film of the processing solution, the belt is passed through a belt dryer to dry the wet film. After drying, a dry coating of the conversion layer formed in this way from 2 mg / m ² to 30 mg / m ² remains on the surface of the black plate per side. The desired dry coverage of the conversion layer can be adjusted by the amount of treatment solution fed to the rotary sprayer per unit of time.

An advantage of this type of application is that only fresh treatment solution is used and that it can not be contaminated by iron separation by contact and recycling with the steel strip. In addition, it has been shown that the process is very economical, since only the exact required amount is applied and no excess is required, whereby excess treatment solution no longer needs to be collected. This can prevent that post-treated wastewater arise.

Alternatively, the application of the treatment solution can also Rolling coater by a roller application - also on a previously dried black plate surface - done. Roll coaters are preferably used in the lower speed range of the belt speed and in particular at speeds of less than 200 m / min. Alternatively, the application can also be carried out by spraying the treatment solution or by immersing the tape in a bath with the treatment solution. In this case, since the treatment solution is applied in excess to the black plate, it is necessary to achieve a predetermined desired edition of the conversion layer, squeeze off the excess portion of the wet film, for example by means of squeezing rollers, which can be done "wet on wet". In this method, however, the solution is not applied the same constant regardless of the speed and the treatment solution can also be contaminated by iron and must then be renewed and disposed of after exceeding a contamination threshold.

The wet film of the treatment solution applied with the described application methods is finally dried to form a dry conversion layer. This can be done, for example, by passing the black plate through a drying oven in which wet film is dried by means of hot air or IR radiation. Drying is preferably carried out at temperatures of 50-250 ° C. Finally, the surface of the dry conversion layer is oiled or post-treated with dioctyl sebacate (DOS), acetyltributyl citrate (ATBC), butyl stearate (BSO) or polyalkylene glycol, in particular polyethylene glycol (PEG, preferably having a molecular weight of 6000 g / mol) or combinations thereof. Aftertreatment by oiling with DOS, ATBC, BSO or PEG is advantageously carried out electrostatically with commercially available oilers as in ECCS or tinplate, or else by means of a rotary sprayer.

• – metallische Bestandteile: ausgewählt aus Ti, Zr, Mn, Zn, P und Kombinationen davon;
• – organische Bestandteile: ausgewählt aus Polyacrylat, Polycarboxylat und Kombinationen davon.

The aqueous treatment solution used for the conversion coating preferably contains at least one of the following substances:

• Metallic constituents: selected from Ti, Zr, Mn, Zn, P and combinations thereof;
• - Organic ingredients: selected from polyacrylate, polycarboxylate and combinations thereof.

Metallic and organic components can in turn be combined.

The treatment solution further contains at least one adhesion promoter for paints or organic coating materials, the adhesion promoter in particular containing constituents of maleic acid, isophthalic acid and cyclohexanedimethanol (CHDM) or combinations thereof. Particularly suitable adhesion promoters have proven compositions containing polyethylene terephthalate (PET) or Polycyclohexylendimethylenterephthalat (PCT), such. B. glycol-modified polyethylene terephthalate (PET-G, which contains less than about 30% CHDM) or PCTG (which contains more than about 30% CHDM).

The requirements are 1 to 50 mg / m ² for the respective substances.

Listed below are a few selected commercially available agents suitable for producing conversion coatings by the method of the present invention. trade name Essential chemical ingredient Manufacturer / Supplier - polycarboxylates ^BASF® EFKA ^® 4560 modified polyacrylates ^BASF® - Ti, Zn, Mn phosphate Henkel ^® Granodine ^® 1456 Ti, Zr Henkel ^® GTP 10861 Gardo ^® TP Zn phosphates Ti Chemetall ^® GB X4744A Gardobond ^® (Chemetall ^®) Mn, Ti, Zr Chemetall ^® GB X4591 Al Ti, Zr Chemetall ^® GB X4744 Ti, Zr Chemetall ^®

• a) eine wässrige Lösung, die Aluminiumfluorozirkonat mit einem Molverhältnis von Al:Zr:F von (0,15 bis 0,67):1:(5 bis 7) enthält, wobei die Gesamt-Konzentration von Al + Zr + F 0,1 bis 2,0 g/l beträgt und der pH-Wert auf weniger als 5, vorzugsweise 3 bis 5 eingestellt ist.
• b) eine wässrige Lösung, die im Wesentlichen enthält:
• – 0,2 bis kleiner 10 g/l Zinkionen,
• – 0,5 bis 25 g/l Manganionen und
• – 2 bis 300 g/l Phosphationen, gerechnet als P₂O₅, wobei das Zink:Mangan-Gewichtsverhältnis der Phosphatierungslösung im Bereich von 0,05:1 bis 1:1 gehalten wird.
• c) eine wässrige Lösung, die Zink und Mangan enthält, mit Zink im Bereich von 0,05 bis 5 g/l, Mangan im Bereich von 0,075 bis 5,2 g/l sowie Kupfer im Bereich von 0,008 bis 0,05 g/l und/oder insgesamt 0,002 bis 0,5 g/l an Hexafluoridkomplexen von Bor, Aluminium, Titan oder/und Zirkonium, berechnet als F₆.
• d) eine wässrige Lösung mit mindestens einem Filmbildner, der mindestens ein wasserlösliches oder wasserdispergiertes Polymer mit einer Säurezahl im Bereich von 5 bis 200 enthält, und mindestens einer anorganischen Verbindung in Partikelform mit einem mittleren Partikeldurchmesser gemessen an einem Rasterelektronenmikroskop im Bereich von 0,005 bis 0,3 μm Durchmesser, wobei das Polymer aus mindestens einem Kunstharz auf der Basis von Acrylat, Ethylen, Polyester, Polyurethan, Siliconpolyester, Epoxid, Phenol, Styrol, Harnstoff-Formaldehyd, deren Derivate, Copolymere, Polymere, Mischungen oder/und Mischpolymerisate ausgewählt ist und die anorganische Verbindung in Partikelform aus mindestens einer Verbindung des Aluminiums, Siliciums, Titans, Zinks oder/und Zirkoniums ausgewählt ist. oder
• e) eine wässrige Lösung mit
• i) mindestens einem organischen Filmbildner, der mindestens ein wasserlösliches oder wasserdispergiertes Polymer enthält, das ein Kunstharz auf der Basis von Polyacrylsäure, Polyacrylat oder/und Polyethylen-Acryl-säure ist oder ein Kunstharzgemisch oder/und ein Mischpolymerisat mit einem Gehalt an Kunstharz auf der Basis von Acrylat bzw. Polyacryl, darstellt und
• ii) einem Gehalt an Kationen oder/und Hexa- oder Tetrafluorokomplexen von Kationen ausgewählt aus der Gruppe von Titan, Zirkonium, Silicium, Aluminium und Bor im Bereich von 0,2 bis 30 g/l bezogen auf den Gehalt des elementaren Metalls.

Preferred treatment solutions for producing the conversion layers can be composed, for example, as follows:

• a) an aqueous solution containing aluminum fluorozirconate having a molar ratio of Al: Zr: F of (0.15 to 0.67): 1: (5 to 7), wherein the total concentration of Al + Zr + F is 0, 1 to 2.0 g / l and the pH is adjusted to less than 5, preferably 3 to 5.
• b) an aqueous solution containing essentially:
• 0.2 to less than 10 g / l zinc ions,
• - 0.5 to 25 g / l manganese ions and
• 2 to 300 g / l of phosphate ions, calculated as P ₂ O ₅ , with the zinc: manganese weight ratio of the phosphating solution being maintained in the range of 0.05: 1 to 1: 1.
• c) an aqueous solution containing zinc and manganese with zinc in the range of 0.05 to 5 g / l, manganese in the range of 0.075 to 5.2 g / l and copper in the range of 0.008 to 0.05 g / l and / or a total of 0.002 to 0.5 g / l of hexafluoride complexes of boron, aluminum, titanium or / and zirconium, calculated as F ₆ .
• d) an aqueous solution comprising at least one film-forming agent which comprises at least one water-soluble or water-dispersed polymer having an acid number in the range from 5 to 200, and at least one inorganic compound in particle form having a mean particle diameter measured on a scanning electron microscope in the range from 0.005 to 0, 3 μm in diameter, the polymer being selected from at least one synthetic resin based on acrylate, ethylene, polyester, polyurethane, silicone polyester, epoxide, phenol, styrene, urea-formaldehyde, their derivatives, copolymers, polymers, mixtures or / and copolymers and the inorganic compound is selected in particulate form from at least one compound of aluminum, silicon, titanium, zinc or / and zirconium. or
• e) an aqueous solution with
• i) at least one organic film former containing at least one water-soluble or water-dispersed polymer which is a synthetic resin based on polyacrylic acid, polyacrylate and / or polyethylene-acrylic acid or a synthetic resin mixture or / and a copolymer containing a synthetic resin on the Basis of acrylate or polyacrylic, represents and
• ii) a content of cations and / or hexa- or tetrafluoro complexes of cations selected from the group consisting of titanium, zirconium, silicon, aluminum and boron in the range from 0.2 to 30 g / l based on the content of the elemental metal.

The inventive method can be installed without major installation effort in an existing coating system, for. B. in a coil coating plant for the production of ECCS (or TFS) are integrated. The belt speed in such belt coater is typically 80-600 m / min.

The inventive method has the advantages of a chromium-free and therefore environmentally friendly and not hazardous to health and cost-effective coating on conventional black plate, especially in the fine and Feinstblech thickness range. In addition, by the selected application method (no-rinse method) for applying the conversion layer by eliminating the final rinse effective cost and energy savings can be achieved. In particular, advantages are achieved by the combination of inorganic passivation and polymer-containing thin-film coating. The black sheets treated by the process of the invention are eminently suitable for the production of packaging, in particular cans, and can therefore replace the tinplates and tin-free steel sheets (TFS or ECCS) conventionally used as packaging steel. These black sheets are comparable in their corrosion resistance with tinplate and have similarly good adhesion properties for paints and plastic coatings, for example of PP or PET, on as tin-free steel sheets (TFS or ECCS).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 97/40208-A [0006]
• EP 2532769 A1 [0006]
• WO 2008/119675 [0006]

Cited non-patent literature

• DIN EN 10202: 2001: "Cold-rolled sheet-metal products (electrolytically tin-plated and chromium-plated)" [0012]

Claims (16)

Process for the passivation of strip-shaped black plate, comprising the following steps: Electrochemical treatment of the black plate by passing the black plate through an electrolyte to form an inert steel surface, - rinsing the black plate, - Applying an aqueous chromium-free treatment solution on at least one surface of the black plate to form a corrosion-protective conversion layer and an adhesive layer for paints and organic coating materials. The method of claim 1, wherein the black sheet is first degreased prior to the electrochemical treatment, then rinsed, pickled and rinsed again. The method of claim 1 or 2, wherein after the application of the treatment solution, the black plate is dried to form a dry coating of the processing solution on the blackplate surface. Method according to one of the preceding claims, wherein the electrochemical treatment is carried out by passing the black plate through an alkaline electrolyte with switching the black plate as an anode. Method according to one of the preceding claims, wherein the conversion layer is applied by applying the aqueous treatment solution in the no-rinse process. The method of claim 5, wherein the aqueous treatment solution either applied without excess with a rotary sprayer on the black plate or applied in excess with a roll coater or spray nozzles and then the excess treatment solution is squeezed off with squeezing rollers. The method of claim 3, wherein the drying is carried out at 50-250 ° C. Method according to one of claims 3 to 7, wherein the dry coating of the treatment solution after drying with DOS, ATBC, BSO or a polyalkylene glycol, in particular polyethylene glycol (PEG), aftertreated. Method according to one of claims 3 to 8, wherein the dry coverage of the treatment solution is between 1 mg / m ² and 50 mg / m ² . A method according to any one of the preceding claims, wherein the black sheet is moved at a belt speed of at least 200 m / min. Method according to one of the preceding claims, wherein the black plate is a cold-rolled, annealed and re-rolled, in particular ferritic or multi-phase steel sheet having a carbon content of 20 to 1000 ppm. Method according to one of the preceding claims, wherein the temperature of the electrolyte in the electrochemical treatment of the black plate between 20 and 50 ° C. Method according to one of the preceding claims, wherein the current density in the electrochemical treatment of the black plate is between 2 and 10 A / dm ² . Process according to any one of the preceding claims, wherein the aqueous treatment solution is chromium-free and contains at least one of the following constituents: Metallic constituents: selected from Ti, Zr, Mn, Zn, P and combinations thereof; - Organic ingredients: selected from polyacrylate, polycarboxylate and combinations thereof. A method according to claim 1, characterized in that the treatment solution contains at least one adhesion promoter for paints or organic coating materials, wherein the adhesion promoter in particular components of maleic acid, isophthalic acid and cyclohexanedimethanol (CHDM) or combinations thereof. Use of a black plate treated by a method according to the preceding claims, having a chromium-free conversion layer on at least one surface of the black plate, as packaging steel for producing packaging, in particular cans.