RU2663232C2 - Method of passivation of strip-shaped black plate - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to the passivation of strip-shaped black plate. Method includes passing a strip of cold-rolled, hardened and rolled black plate with a carbon content of 20 to 1000 millionby weight through a coating machine for strip steel with a strip speed of at least 200 m/min, cleaning and degreasing said strip in an alkaline solution of sodium hydroxide or potassium hydroxide and washing it, electrochemical treatment of the strip in an alkaline electrolyte at a current density of 2 to 30 A/dmwith a steel strip connected as an anode, washing it and drying it, application of an aqueous chromium-free solution to form a conversion layer on the surface of the strip and a bonding layer for paints and organic coating materials. Solution used contains the following components: a) titanium and zirconium, or b) titanium, zirconium and manganese, or c) titanium, zinc and phosphates, or d) titanium, zinc, manganese and phosphates.EFFECT: black plates treated using said method are highly corrosion resistant, have good adhesiveness with paints and organic coatings, and are very well suited as a substitute for tin-free steel sheet and tin plate for the production of packages, in particular cans.13 cl, 1 tbl

Description

The invention relates to a method for passivation of strip black metal, in which, during the first stage, an inert layer is formed on the surface of the black sheet by electrochemical processing of the black sheet, and during the next stage, an anhydrous chromium-free treatment solution is applied to at least one surface of the black sheet to form a protective sheet. from corrosion of the conversion layer, which, in addition, forms an adhesive layer for paints and organic coating materials. By passivation in the context of the present invention is meant the targeted preparation of a protective layer (here: a conversion layer) on black metal, which prevents the corrosion of black metal or at least greatly slows it down. The invention also relates to the use of black sheet processed according to the present invention as packaging steel.

Known methods of protecting metal surfaces from corrosion, in which metal coatings provide a coating of another, usually non-precious, metal (for example, zinc and chromium). For example, it is known that coatings made of zinc or chromium or tin (which, however, is a more noble metal than steel) are coated on steel sheet. For the manufacture of packaging, in particular in the field of food, it is very widely used, for example, tinned thin sheets (white sheets). Tinplate has very good corrosion resistance and good formability and weldability, and therefore it is very well suited for the manufacture of packaging, such as cans for drinks.

In order to protect the metal coating itself, such as tin coating in the case of tinplate, from corrosion and to provide a good adhesive primer for paints and polymer coatings, conversion layers are often applied to the surface of the metal coating.

By conversion layers is meant non-metallic, most often inorganic, very thin layers on the metal surface, which, as a rule, are formed by the chemical reaction of an aqueous solution for processing with a metal base. Conversion coatings provide, in particular in the case of thin gestures, a very effective corrosion protection, good adhesion primer for paints and polymer coatings, and they reduce surface friction and wear.

Depending on the basis, iron, zinc and manganese phosphating, electrolytic phosphating, chromate, oxalate methods and anodizing are distinguished. The chromium-containing conversion layers proved to be very effective corrosion protection. When chromating, the metal surface is treated with an acidic solution containing chromium (VI) ions, while chromium (VI) is reduced to chromium (III). As a result of processing, a chromium-containing conversion layer that protects against corrosion is formed on the metal surface.

However, chromium (VI) compounds are highly toxic and carcinogenic. In automotive applications and household appliances, the passivation of metal surfaces with substances containing chromium (VI) is already prohibited in the EU. For this reason, chrome-free conversion layers have been developed in the prior art. Thus, for example, from WO 97/40208-A and EP 2532769 A1, methods are known for producing chromium-free conversion layers on zinc or aluminum surfaces. WO 2008/119675 also describes surface treatment solutions for the preparation of chrome-free conversion layers that contain oxocations and complex halogen ions, which lead to colorless and slightly iridescent conversion layers.

Tinplate has excellent properties for use as a packaging material for food products, and for many decades it has been manufactured and processed for this purpose. However, tin, which in the case of tinplate forms an anti-corrosion coating, has turned into a very expensive material due to a worldwide shortage of resources. As an alternative to tinplate, in particular for use as packaging steel, chrome-plated steel sheets known as tinless gestures (TFS; from the English Tin Free Steel) or “electrolytically chrome-plated steel” (ECCS) are known in the prior art. ; from the English Electrolytic Chromium Coated Steel). These tinless tins are distinguished, on the one hand, by good adhesion to paints or organic protective coatings (for example, from PP (polypropylene) or PET (polyethylene terephthalate)), however, on the other hand, when implementing the coating method, it is toxic and harmful to The health properties of chromium-VI-containing materials used for coating have significant drawbacks.

It is therefore an object of the present invention to provide a chromium-free packaging sheet which is suitable for use as a replacement for tinless sheet metal (TFS or ECCS) and as a replacement for white sheet, and which, in particular, both in terms of corrosion resistance and properties adhesion to paints or organic coatings should be comparable to white tin or tinless steel tin.

This problem is solved by the method of passivation of strip black sheet with signs according to paragraph 1 of the claims. According to this method, uncoated tinplate is used in strip form and its surface is inert during the first stage by electrochemical treatment, then it is washed with water or another washing liquid, and finally, at the additional stage, a corrosion-resistant conversion coating is applied by applying an aqueous chromium-free solution for processing at least on one surface of black tin.

Other specific embodiments of the method are defined in the dependent claims.

Preferably, a cold-rolled, hardened and dovaltsovannuyu or a trained steel strip of unalloyed steel with a carbon content of from 20 to 1000 million ^-1. Preferably, the steel strip (black sheet) had the following properties:

- strength: 300-1000 MPa

- tensile elongation: 1-40%

- thickness: 0.05-0.49 mm

- surface roughness: 0.1-1 microns

As for steel, it can be, for example, ferritic steel or multiphase steel, which contains numerous structural elements, in particular ferrite, martensite, bainite and / or residual austenite. Such multiphase steels are characterized by high strength exceeding 500 MPa, while at the same time good tensile elongation exceeding 10%. Regarding the intended use of black sheet processed according to the present invention as packaging steel, it is preferable to use steel grades defined in DIN EN 10202: 2001: “Cold-rolled packaging sheet (electrolytic tinning or chromium plating)”. This standard, among other things, defines the analyzes and mechanical characteristics of steel. In particular, the grades of tin are determined by the range from TS230 (soft tin annealed in a bell furnace, yield strength 230 MPa) to TN620 (the same, 620 MPa).

In order to carry out the method of the present invention, strip-shaped black metal is moved at a speed that is preferably greater than 200 m / min and up to 750 m / min. First, the stage of forming an inert layer on the surface of the black sheet is carried out by electrochemical processing. In preparation for the electrochemical treatment, the movable strip of black metal is first cleaned during the optional pretreatment stage and, in particular, degreased, then washed, pickled and washed again. This is necessary under certain conditions, since cold rolled and recrystallized-annealed black tin after recrystallization annealing is usually rolled or trained, while, for example, wet rolling using a water-oil suspension or dry rolling of black metal surfaces can be contaminated with oil, iron dust , soaps and other impurities. This contamination is removed during the (optional) pretreatment step.

To do this, black tin is sent to a purification tank containing an alkaline solution of sodium hydroxide or potassium hydroxide. The concentration of alkaline degreasing agent preferably lies in the range from 20 g / l to 100 g / l at temperatures in the tank lying in the range from 20 ° C to 70 ° C. It is advisable to degrease black metal in two stages, moreover, the immersion method is used during the first stage, and the electrolytic method with current densities in the range from 2 A / dm ² to 30 A / dm ^{2 is} used during the second stage. After degreasing, each side of the strip of black metal is washed using, for example, a three-stage washing and a water volumetric velocity lying in the range from 10 m ³ / h to 30 m ³ / h of water. If necessary, the removal of oxide residues can be carried out by feeding a strip of black tin to the next cleaning tank containing an etching solution based on salt or sulfuric acid with a concentration lying, for example, in the range from 10 g / l to 120 g / l, in the form of two successive dives and subsequent washing in a sink in the form of an immersion. The temperatures of the pickling solution and wash water typically range from 20 ° C to 60 ° C.

After pretreatment, an even, dense, inert surface of the sheet is obtained by electrochemical treatment by passing strip black sheet through an electrolyte. The electrolyte is preferably alkaline. The electrochemical, preferably alkaline, treatment of black sheet ensures the inertization and leveling of the surface properties of the steel strip before applying the conversion coating.

During the stage of the electrochemical treatment, the strip black metal is passed through the electrolytic bath at a certain speed and is used as an anode with a preferred current density lying in the range from 2 A / dm ² to 30 A / dm ² . The electrolytes are, for example, a sodium hydroxide solution with a preferred NaOH concentration in the range of 20 g / l to 100 g / l, and in particular, a sodium hydroxide bath with a 3% NaOH solution is used. You can use a solution of soda as an electrolyte, in particular a 3% solution of sodium carbonate (Na ₂ CO ₃ ). The temperatures in the electrolytic bath, it is advisable to maintain in the range from 20 ° C to 80 ° C.

After electrochemical treatment, the black tin is washed with water. Rinsing can be done by immersing the strip in a tank of water or by spraying with water. It is preferable to use completely desalinated (VE; from German: vollentsalzt) deionized water, osmotic water or distilled water with a temperature in the range from 20 ° C to 60 ° C. However, untreated tap water or other flushing fluids can also be used. After washing, the black tin is dried.

In conclusion, during the last stage, at least one surface of the black sheet is applied to the conversion layer, for this an aqueous chromium-free solution for surface treatment is applied to the surface of black sheet previously inertized by electrochemical treatment.

In this case, it is advisable to apply the conversion coating by a non-washing method, which means that there is no washing after the formation of the conversion layer. An aqueous chromium-free surface treatment solution that forms a conversion coating is then applied to the surface of the black sheet using a coating device that includes a coating roller, a rotary atomizer, or spray nozzles.

It is preferable to use an application device equipped with a rotary atomizer for applying an aqueous solution for surface treatment. To apply the solution for surface treatment, the surface of the black sheet, on which the conversion layer should be applied, should be as clean and dry as possible. Therefore, at least one surface of the black sheet on which the conversion layer is to be applied is dried using a drying device, for example with an air knife. Using this air knife, a laminar flow of hot air is blown over the surface of the moving strip, so that interfering foreign particles are blown off the surface of the steel strip, and the surface of the steel strip is dried.

The rotary sprayer contains several spraying rotors located next to each other and across the direction of movement of the strip, to which an aqueous solution for surface treatment is supplied, and which are driven by a drive so that, under the action of centrifugal force, a water solution for surface treatment is sprayed in the form of a finely dispersed jet surface or both surfaces of the strip and create a wet film of an aqueous solution there. After applying a wet film of an aqueous solution for surface treatment, it is evenly distributed on the surface of the black sheet using drive rolls. In this case, it is advisable to arrange the rolled rollers relative to the surface (or surfaces) of the black sheet so that only a slight pressure is created on the wet film of the surface treatment solution and generally is not squeezed out from the surface or only a minimal fraction of the applied surface treatment solution is squeezed out. Accordingly, the amount of surface treatment sprayed by the rotary spray gun is selected so that no excess solution appears on the surface of the black sheet. Due to this, there is no need to remove or prepare an excess amount of surface treatment solution, which is otherwise necessary. After even distribution of the wet film applied by spraying, it is dried, so that a dry residue of the substance used for processing remains on the treated black sheet surfaces. It is advisable that the dry precipitate of the surface treatment solution after drying is from 1 mg / m ² to 50 mg / m ² , and preferably from 10 mg / m ² to 30 mg / m ² . The amount of aqueous solution for surface treatment, supplied to the spray rotors of the rotary sprayer per unit time, it is advisable to choose in accordance with the speed of the strip. Due to this, it can be ensured that only the required exact amount of fresh mortar for surface treatment in the appropriate concentration is applied by a wet film rotary sprayer to the strip black sheet. So, for example, you can set the continuous application of a wet film in the range from 2 ml / m ² to 8 ml / m ² , preferably about 5 ml / m ² , on each side of the strip, regardless of the speed of the strip.

After applying a wet film of the surface treatment solution, the strip is passed through the strip drying apparatus to dry the wet film. After drying, a dry precipitate of the thus obtained conversion layer remains on the surface of the black sheet, comprising on each side from 2 mg / m ² to 30 mg / m ² . In this case, the desired dry sediment mass can be adjusted due to the amount of surface treatment solution supplied by the rotary sprayer per unit time.

The advantage of this application method is that only fresh mortar is constantly used for surface treatment, and it cannot be contaminated with detachable iron during contact with the steel strip and reuse. In addition, it was shown that the method is very economical, since only the required amount is applied and the excess solution is not needed, therefore, it is not necessary to collect the excess solution for surface treatment. Due to this, it is possible to avoid the formation of wastewater requiring further treatment.

Alternatively, it is possible to apply the solution for surface treatment by means of a coating roller by means of a roll application, also on a previously dried surface of black sheet. Cover rollers are preferably used at a strip speed in the lower speed range and, in particular, at speeds of less than 200 m / min. Alternatively, it is possible to apply both by spraying the coating solution or by dipping the strip in the bath with the surface treatment solution. Since in this case the surface treatment solution is applied in excess to the black sheet, in order to obtain a predetermined desired deposition of the conversion layer, it is necessary to squeeze out the excess part of the wet film, for example, using squeeze rollers, which can be done “wet on wet”. In this method, the solution is not applied evenly at all, regardless of speed, and the surface treatment solution may be contaminated with iron; therefore, it must be replaced and destroyed after exceeding the threshold concentration of pollution.

Finally, the wet film of the surface treatment solution applied as described above is dried to obtain a dry conversion layer. This can be done, for example, by passing black metal through a drying oven, in which the wet film is dried using hot air or infrared radiation. Drying is preferably carried out at temperatures ranging from 50 ° C to 250 ° C. The surface of the dry conversion layer is then lubricated or treated with dioctyl sebacate (DOS; dioctylsebacat), acetyl tributyl citrate (ATBC; acetyltributylcitrate), butyl stearate (BSO; english butylstearate), or polyalkylene glycol; polyethyleneglycol), preferably with a molecular weight of 6000 g / mol), or a combination thereof. Further processing by lubrication with DOS, ATBC, BSO or PEG is advantageously carried out electrostatically using commercially available lubricating apparatus, as in the case of ECCS or tinplate, or using a rotary atomizer.

The surface treatment solution used to obtain the conversion coating preferably contains at least one of the following substances:

- metal components: selected from Ti, Zr, Μn, Ζn, Ρ and their combinations;

- organic components: selected from polyacrylate, polycarboxylate and combinations thereof.

Metallic and organic components can also be combined.

In addition, the surface treatment solution contains at least one adhesion promoter for paints or organic coating materials, and the adhesion promoter, in particular, contains maleic acid, isophthalic acid and cyclohexanedimethanol (CHDM; cyclohexanedimethanol) or combinations thereof . Particularly suitable adhesion enhancers have been shown to be compositions that contain polyethylene terephthalate (PET; from English: polyethyleneterephtalate) or polycyclohexylene dimethylene terephthalate (PCT; from English: polycyclohexylenedimethyleneterephthalate), for example, glycol-modified polyethylene terephthalate (less than about 30% PET) CHDM) or PCT-G (which contains more than about 30% CHDM).

The amounts applied are from 1 mg / m ² to 50 mg / m ² for the respective substances.

The following are some selected commercially available agents that are suitable for preparing conversion coatings by the method of the present invention.

Preferred surface treatment solutions used to produce conversion layers may, for example, have the following composition:

a) an aqueous solution that contains aluminum fluorozirconate with a molar ratio of Al: Zr: F equal to (from 0.15 to 0.67): 1: (from 5 to 7), and the total concentration of Al + Zr + F is from 0 , 1 to 2.0 g / l, and the pH value is set to less than 5, preferably from 3 to 5;

b) an aqueous solution that essentially contains:

- from 0.2 g / l to less than 10 g / l of zinc ions,

- from 0.5 g / l to 25 g / l of manganese ions and

- from 2 to 300 g / l of phosphate ions, in terms of P ₂ O ₅ ,

moreover, the mass ratio of zinc: manganese in the solution for phosphating is maintained in the range from 0.05: 1 to 1: 1;

c) an aqueous solution containing zinc and manganese, wherein the concentration of zinc is in the range from 0.05 to 5 g / l, the concentration of manganese is in the range from 0.075 g / l to 5.2 g / l, as well as copper with a concentration of a range of from 0.008 g / l to 0.05 g / l and / or a total of from 0.002 g / l to 0.5 g / l of hexafluoride complexes of boron, aluminum, titanium and / or zirconium, in terms of F ₆ ;

d) an aqueous solution containing at least one film former that contains at least one water-soluble or water-dispersible polymer with an acid number in the range of 5 to 200, and at least one inorganic compound in the form of particles with an average particle diameter measured using a scanning electron microscope in the range from 0.005 μm to 0.3 μm, the polymer being selected from at least one plastic resin based on acrylate, ethylene, polyesters, polyurethane, silicone polyesters, ep ksida, phenol, styrene, urea-formaldehyde, derivatives, copolymers, polymers, mixtures and / or mixed polymers, and the inorganic compound in particle form selected from at least one compound of aluminum, silicon, titanium, zinc and / or zirconium; or

e) an aqueous solution containing

i) at least one organic film former that contains at least one water soluble or water dispersible polymer, which is a plastic resin based on polyacrylic acid, polyacrylate and / or polyethylene acrylic acid, or a mixture of plastic resins and / or a mixed polymer containing acrylate or polyacrylate-based plastic resin, and

ii) the concentration of cations and / or hexa- or tetrafluorocomplexes of cations selected from the group consisting of titanium, zirconium, silicon, aluminum and boron, in the range from 0.2 g / l to 30 g / l, calculated on the content of elemental metals .

The method of the present invention can be integrated without large installation costs into an existing coating plant, for example a strip steel coating plant in the manufacture of ECCS (or TFS). The speed of the strip in such installations for coating strip steel usually lies in the range from 80 to 600 m / min.

The method of the present invention provides the advantages of chromium-free and therefore environmentally friendly and human health, as well as cost-effective coating on standard black sheet, in particular in the thin and ultrathin thickness ranges. In addition, with the selected application method (non-washing method) of the conversion coating, due to the exclusion of the final washing, significant savings in money and energy are provided. Additional advantages are provided, in particular, due to a combination of inorganic passivation and a thin film coating containing polymeric materials. The black tins processed by the method of the present invention are excellently suited for the manufacture of packages, in particular cans, and therefore can replace the white tins and tinless steel sheets (TFS or ECCS) commonly used as packaging steel. These black sheets are comparable in their corrosion resistance to white tin and have the same good adhesion properties to paints and polymer coatings, such as PP or PET, as well as tinless steel sheets (TFS or ECCS).

Claims (23)

1. The method of passivation of strip black metal, comprising the following stages: - providing cold rolled, hardened and dovaltsovannoy black iron with a carbon content of from 20 to 1000 million by weight of ^-1 and passing said strip through the apparatus for coating the steel strip with the strip movement speed of at least 200 m / min; - cleaning and degreasing the specified strip by passing the specified strip with the specified speed of the strip through the cleaning tank filled with an alkaline solution of sodium hydroxide or potassium hydroxide, and then washing the strip; - conducting an electrochemical treatment of the indicated strip by passing the specified strip with the specified speed of the strip through an alkaline electrolyte at a current density of 2 to 30 A / dm ² with a steel strip connected as an anode, where the electrolyte is a solution of sodium hydroxide or soda and it is maintained at temperatures in the range from 20 to 80 ° C; - washing and drying said strip; - applying an aqueous chromium-free solution for processing on at least one surface of the specified strip to form a corrosion-resistant conversion sheet of black tin and forming a binder layer for paints and organic coating materials, where the specified aqueous solution for processing is applied to the strip when it moves at a specified speed lane movements; wherein the treatment solution contains the following essential chemical components: a) titanium and zirconium, b) or titanium, zirconium and manganese, c) or titanium, zinc and phosphates, d) or titanium, zinc, manganese and phosphates. 2. The method according to p. 1, characterized in that the steel strip is additionally pickled and washed after degreasing and before electrochemical treatment.  3. The method according to p. 1 or 2, characterized in that the strip after applying the solution for processing is dried, preferably at a temperature of from 50 to 250 ° C, to form a dry coating from the solution for processing on the surface of the strip. 4. The method according to p. 3, characterized in that the aqueous solution for processing without excess is applied to the strip using a rotary spray. 5. The method according to p. 3, characterized in that the aqueous solution for processing in excess is applied to the strip using a coating roller or spray nozzles, and then the excess solution for processing is squeezed out using squeeze rollers. 6. The method according to p. 3, characterized in that the dry coating from the solution for processing is additionally treated with dioctyl sebacate (DOS), acetyl tributyl citrate (ATBC), butyl stearate (BSO) or polyalkylene glycol, in particular polyethylene glycol (PEG). 7. The method according to p. 3, characterized in that the dry coating from the solution for processing is from 1 to 50 mg / m ² . 8. The method according to p. 1, characterized in that said strip is a ferritic or multiphase black sheet. 9. The method according to p. 1, characterized in that the temperature of the electrolyte during the electrochemical treatment of the steel strip lies in the range from 20 to 50 ° C. 10. The method according to p. 1, characterized in that the current density during the electrochemical processing of black sheet lies in the range from 2 to 10 A / DM ² . 11. The method according to p. 1, characterized in that the aqueous solution for processing contains organic components selected from polyacrylates, polycarboxylates and their combinations. 12. The method according to p. 1, characterized in that the solution for processing contains at least one adhesion promoter for paints or organic coating materials. 13. The method according to p. 12, characterized in that the adhesion promoter contains maleic acid, isophthalic acid or cyclohexane dimethanol (CHDM), or a combination thereof.