EP3434807A1 - Steel sheet having a conversion layer, method for producing a conversion coated steel sheet and treating agent for applying a conversion layer on a steel sheet - Google Patents

Abstract

Provided is a steel sheet, in particular a strip-shaped black sheet, with a conversion layer, which is produced from components dissolved in water, wherein the components are selected from
i) hexafluorotitanate,
ii) zinc phosphate,
iii) phosphoric acid,
iv) a mixture of any of i) to iii),
with the proviso that components i), ii) and iii) contain no organic constituents.

Description

The invention relates to a steel sheet with a conversion layer, a method for producing a conversion-coated steel sheet and a treatment agent for applying a conversion layer on a steel sheet.

To protect metallic surfaces from corrosion, methods are known in which the metallic surface is provided with a coating of another, usually less noble, metal (such as zinc and chromium). So it is e.g. known to coat steel sheets with zinc or chromium or with tin (which, however, is nobler compared to steel). 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. Beverage cans.

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 good adhesion to paints or organic protective coatings (for example PP or PET), but on the other hand have considerable disadvantages in carrying out the coating process because of the toxic and health-endangering properties of the chromium-VI-containing materials used for coating ,

In order to protect the steel sheet against corrosion and to produce a good primer for paintwork and plastic coatings, conversion coatings are often applied to the steel sheet surface. The targeted generation of a conversion layer on a steel sheet (black plate) prevents corrosion of the steel sheet or slows them at least strong.

Conversion layers are non-metallic, very thin layers on a metal surface, which are usually produced by chemical reaction of an aqueous treatment solution with the metallic substrate. Conversion coatings ensure a very effective corrosion protection, a good primer for paints and plastics, especially for thin steel sheets (fine plates with thicknesses in the range of 0.1 to 0.5 mm) and they reduce surface friction and abrasion.

Electrolytic methods for applying conversion layers to steel sheets are known from the prior art. Conversion views were often generated with chromium electrolytes based on the carcinogenic chromium (VI) oxide. However, chromium (VI) -containing conversion layers are used less and less frequently due to legal prohibitions. Alternatives to the classic chromium (VI) electrolyte are treatments based on chromium (III) oxide or complex fluorides (titanium, zirconium compounds). Another possibility for producing a conversion layer is the phosphating by means of aqueous phosphate solutions.

From the DE 101 61 383 A1 discloses a process for coating metallic surfaces, including steel surfaces, with an aqueous composition free of chromium (VI) compounds, the aqueous composition containing, in addition to the water solvent, at least one organic film former containing a water-soluble or water-dispersed polymer containing cations and / or hexa- or tetrafluoro complexes of cations selected from Ti, Zr, Hf, Si, Al and B, at least one inorganic compound in particle form with a particle diameter of 0.005 μm to 0.2 μm and optionally a silane and / or siloxane and also optionally contains a corrosion inhibitor.

Conventional, commercially available, chromium-free means for producing conversion coatings on metal contain either film formers or organic solvents. Film formers are typically polymers which impart various useful properties, such as adhesiveness, to the conversion layer. However, these polymers require an increased effort in applying the funds and they make the means more expensive. The solvents contained in conventional, chromium-free conversion-coating agents are generally more expensive than water, represent to some extent a health impairment in applying the conversion layer and in most cases belong to the so-called VOC (Volatile Organic Compound) Environmental reasons should be avoided.

The object of the present invention is therefore to provide a chromium-free agent for producing conversion coatings on steel sheets. The invention is furthermore intended to show steel sheets with a chromium-free conversion layer and a method for their production which can be produced as inexpensively as possible and can be used as a substitute for tin-free steel sheet (TFS or ECCS) and tinplate, and in particular with regard to corrosion resistance and adhesiveness for paints or organic coatings should be comparable to tinplate or tin-free steel sheet.

These objects are achieved with a steel sheet according to claim 1, a method for producing a conversion-coated steel sheet according to claim 7 and by a treatment agent for applying a conversion layer on a steel sheet according to claim 10.

1. i) Hexafluorotitanat,
2. ii) Zinkphosphat und/oder Eisenphosphat,
3. iii) Phosphorsäure,
4. iv) oder ein Gemisch der Komponenten i) bis iii) enthält, wobei die Konversionsschicht keine organischen Stoffe beinhaltet.

The steel sheet according to the invention, which may in particular be a strip-shaped black plate or also a steel sheet coated with a metallic corrosion protection layer, has on at least one surface a conversion layer comprising at least one of the components

1. i) hexafluorotitanate,
2. ii) zinc phosphate and / or iron phosphate,
3. iii) phosphoric acid,
4. iv) or a mixture of components i) to iii), wherein the conversion layer contains no organic substances.

The conversion layer preferably consists of one of the components i) to iii) or of a mixture of these components, more preferably of a mixture of components i) and ii) or a mixture of all three components i), ii) and iii).

To produce the steel sheet according to the invention, a metal-coated or uncoated steel sheet (black sheet) is used, the surface is degreased in a first process step, then rinsed with water or another rinsing liquid and finally in a further step, a wet film of a conversion layer is applied by at least one degreased Surface of the steel sheet, a wet film of a chromium-free treatment solution consisting solely of inorganic components, is applied, wherein the wet film of the conversion layer of water-dissolved components is produced and the components are selected from hexafluorotitanate, zinc phosphate and / or iron phosphate, phosphoric acid, and / or a mixture of these components, with the proviso that the components contain no organic substances and also no inorganic particles with an average particle diameter of more than 0.005 microns. The volume of the wet film is preferably in the range of 1 ml / m ² to 10 ml / m ² . The wet film of the conversion layer is finally dried in a last step of the process according to the invention.

Preferably, the chromium-free treatment solution consists only of water and one of the components hexafluorotitanate, zinc phosphate and / or iron phosphate or phosphoric acid, or a mixture of these components, more preferably from a mixture of the components hexafluorotitanate and zinc phosphate or a mixture of the components hexafluorotitanate, zinc phosphate and phosphoric acid. During drying of the wet film of the conversion layer produced from the aqueous treatment solution, the solvent (water) evaporates, so that the dried conversion layer consists in these preferred embodiments only of the effective components of the chromium-free treatment solution, ie hexafluorotitanate, zinc phosphate and / or iron phosphate and phosphoric acid, or a mixture of these active components.

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

Preferred embodiments of the invention are defined in the dependent claims. The invention will be explained in more detail below:
The starting product of a steel sheet according to the invention is preferably a cold-rolled, annealed and tempered steel sheet of a steel with a carbon content of 20-1000 ppm by weight. Suitably, the steel sheet (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 of the steel sheet may, for example, be a ferritic steel or else a multiphase steel having 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 black plate treated according to the invention as a packaging steel, the grades of the steel sheet defined in DIN EN 10202: 2001: "Cold-rolled packaging sheet products (electrolytically tinned and chromium-plated)" are preferably observed. In this standard are u.a. Analysis and mechanical characteristics of the steel defined. The grades are in particular between TS230 (soft hood furnace grade, yield strength 230 MPa) to TH620 (DO, 620MPa). The steel sheet can also be a metal-coated steel sheet, for example an electrolytically tin-plated steel sheet.

To carry out the process according to the invention, the steel sheet, which is preferably in strip form, is moved at a belt speed of preferably more than 200 m / min and up to 750 m / min and subjected to an electrochemical pretreatment. The moving steel sheet is first cleaned and degreased. The cleaning and degreasing is expediently carried out in an electrolyte with switching of the steel sheet as a cathode. Degreasing is expedient because the cold-rolled and recrystallization annealed steel sheet is usually post-rolled or dressed after recrystallization annealing, for example when wet-rolling with a water-oil suspension or even during dry raking the steel sheet surfaces are contaminated by oil, iron abrasion, soaps and other contaminants. This contamination is eliminated by the cleaning step.

For cleaning and degreasing of the steel sheet, the steel sheet can, for example, be passed through 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 remnants may, if necessary, be accomplished by passing the blackplate strip into further cleansing tanks having a hydrochloric acid or sulfuric acid pickling 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 cleaning and degreasing, a further electrochemical treatment of the steel sheet can be carried out to form a homogeneous steel surface, which forms a good adhesion base for a conversion layer. In this further electrochemical treatment, the steel sheet is connected as an anode and passed through an alkaline electrolyte. The alkaline electrolyte may, for example, be a sodium hydroxide solution or a sodium carbonate solution (Na ₂ CO ₃ ).

After the anodic treatment in the alkaline electrolyte, the steel sheet is rinsed with water or other rinsing liquid and then dried. The drying can be carried out, for example, in a continuous furnace or with a blowing device, with which a laminar flow of hot air is blown onto the surface of the moving steel sheet.

After rinsing and drying, the application of the conversion layer to at least one surface of the steel sheet. This is a wet film of an aqueous, chromium-free and based solely on inorganic components Treatment solution applied to the electrochemically pretreated and dried surface of the steel sheet. This can conveniently be done in a no-rinse process in which rinsing is omitted after the application of the wet layer. The aqueous treatment solution which forms the conversion coating can, for example, be applied to the surface of the steel sheet with a roller coater or sprayed with spray nozzles, for example with a rotary sprayer.

After applying the wet film of the processing solution, the conversion layer formed thereby is dried. For this purpose, the steel sheet can, for example, be guided through a belt dryer in order to dry the wet film of the conversion layer. The drying is preferably carried out at temperatures of 50-250 ° C. After the conversion layer has dried, a dry coating of the thus formed conversion layer with a weight per unit area of 1 to 1000 mg / m ² , preferably 10, remains on the surface of the steel sheet (per side) mg / m ² to 400 mg / m ² . The desired dry coverage of the conversion layer can be adjusted by the amount of aqueous treatment solution supplied per unit time in the application step. If necessary, the basis weight of the applied conversion layer can be adjusted before drying by squeezing off excess treatment solution.

Finally, the surface of the dry conversion layer can optionally be aftertreated with dioctyl sebacate (DOS), acetyltributylcitrate (ATBC), butyl stearate (BSO) or polyalkylene glycol, in particular polyethylene glycol (PEG, preferably with a molecular weight of 6000 g / mol), or combinations thereof.

1. i) Hexafluorotitanat,
2. ii) Zinkphosphat und/oder Eisenphosphat,
3. iii) Phosphorsäure,

oder ein Gemisch der Komponenten i) bis iii), mit der Maßgabe, dass die Komponenten i) bis iii), keine organischen Stoffe enthalten.The aqueous treatment solution used for the conversion coating of the steel sheet contains, in addition to the solvent water, at least one of the following components:

1. i) hexafluorotitanate,
2. ii) zinc phosphate and / or iron phosphate,
3. iii) phosphoric acid,

or a mixture of components i) to iii), with the proviso that components i) to iii) contain no organic substances.

• Hexafluorotitansäure [CAS: 17439-11-1],
• Zinkphosphat [CAS: 14485-28-0] und/oder Eisenphosphat [CAS: 10045-86-0],
• ein Gemisch aus Hexafluorotitansäure und Zinkphosphat und/oder Eisenphosphat,
• ein Gemisch aus Hexafluorotitansäure und Phosphorsäure,
• ein Gemisch aus Hexafluorotitansäure, Zinkphosphat und/oder Eisenphosphat und Phosphorsäure oder
• ein Gemisch aus Zinkphosphat und/oder Eisenphosphat und Phosphorsäure.

In preferred embodiments, the aqueous treatment solution, in addition to the solvent water, consists of the following components or mixtures thereof (all proportions and percentages are by weight, unless stated otherwise):

• Hexafluorotitanic acid [CAS: 17439-11-1],
• Zinc phosphate [CAS: 14485-28-0] and / or iron phosphate [CAS: 10045-86-0],
• a mixture of hexafluorotitanic acid and zinc phosphate and / or iron phosphate,
• a mixture of hexafluorotitanic acid and phosphoric acid,
• a mixture of hexafluorotitanic acid, zinc phosphate and / or iron phosphate and phosphoric acid or
• a mixture of zinc phosphate and / or iron phosphate and phosphoric acid.

The effectiveness of the treatment solutions and the properties of the conversion layers are dependent on the concentration of the respective components in the aqueous treatment solution and on the volume coverage of the aqueous treatment solution on the steel sheet surface.

• Hexafluorotitansäure: 1%, 3%, 5%, 7% und 10%, wobei diese Werte auch als Randbereiche für beliebige denkbare Konzentrationsbereiche aufgefasst werden können;
• Zinkphosphat (Zn₃(PO₄)₂₎: 1%, 3%, 5%, 7% und 10% und die entsprechend daraus ableitbaren Konzentrationsbereiche;
• Eisenphosphat (FePO₄₎): 1%, 3%, 5%, 7% und 10% und die entsprechend daraus ableitbaren Konzentrationsbereiche;
• Zinkphosphat (Zn₃(PO₄)₂) und/oder Eisenphosphat (FePO₄) im Gemisch mit Phosphorsäure: Konzentrationsangaben, wie vorstehend für Zinkphosphat und Eisenphosphat) plus 1,4%, 2,3%, 3,2% 4,2% und 5,5% Phosphorsäure und deren entsprechende davon abgeleitete Konzentrationsbereiche;
• TiPO₄, d.h. ein Gemisch aus Hexafluorotitansäure und Zinkphosphat mit einem Zusatz von Phosphorsäure im Verhältnis von 1:2,5:1 bis 4:10:4 bei einer Startkonzentration einer Komponente, wie vorstehend für Hexafluorotitansäure und Zinkphosphat ausgewiesen.

The abovementioned components of the conversion layer can be used, for example, in the aqueous treatment solution in the following concentrations, these concentrations also applying to any mixtures of the components with one another:

• Hexafluorotitanic acid: 1%, 3%, 5%, 7% and 10%, whereby these values can also be regarded as edge regions for any conceivable concentration range;
• Zinc phosphate (Zn ₃ (PO ₄ ) ₂₎ : 1%, 3%, 5%, 7% and 10% and the corresponding concentration ranges derivable therefrom;
• Iron phosphate (FePO ₄₎ ): 1%, 3%, 5%, 7% and 10% and the concentration ranges derived therefrom;
• Zinc phosphate (Zn ₃ (PO ₄ ) ₂ ) and / or iron phosphate (FePO ₄ ) mixed with phosphoric acid: concentration data as above for zinc phosphate and iron phosphate) plus 1.4%, 2.3%, 3.2% 4.2 % and 5.5% phosphoric acid and their corresponding concentration ranges derived therefrom;
• TiPO ₄ , ie a mixture of hexafluorotitanic acid and zinc phosphate with an addition of phosphoric acid in the ratio of 1: 2.5: 1 to 4: 10: 4 at a starting concentration of a Component as identified above for hexafluorotitanic acid and zinc phosphate.

In the case of the conversion layers according to the invention which contain titanium, ie in particular in the conversion layers of hexafluorotitanate or one of a mixture of hexafluorotitanate with a phosphate, a preferred dry coverage based on titanium has in the range from 1 mg / m ² to 50 mg / m ² , preferably in the range from 10 mg / m ² to 40 mg / m ² . In the conversion layers according to the invention containing the phosphate, ie in particular in the conversion layers of or with zinc phosphate or iron phosphate, a preferred dry coating based on phosphate ions in the range of 10 mg / m ² to 1000 mg / m ² and preferably in the range of 100 mg / m ² to 400 mg / m ² .

Examples

Hereinafter, embodiments of the invention will be explained in detail. The specified concentrations of the components of the treatment solutions, which are applied to form a conversion layer on a surface of a steel sheet, refer to the treatment solution itself and not to optionally used batch solutions of higher concentration. All concentrations are based on the weight fractions of the active components in the aqueous treatment solution, regardless of whether the raw materials used even in dilute form, for. B. as aqueous solutions, templates.

For tests on the exemplary embodiments, test sheets in the form of black sheets (uncoated, cold-rolled steel sheets) with a thickness of 0.27 mm were used. The surface of the test panels was first subjected to a cathodic degreasing in 5% sodium carbonate solution Na ₂ CO ₃ (time = 30 s, temperature = 38 ° C, current = 5 A / dm ³ ) and then rinsed with water and demineralized water. A wet film of the aqueous treatment solutions shown in Table 1 was applied to the degreased surface using a roller coater (LARA) and then dried in a drying oven (time = 50 s, temperature 98 ° C.). The resulting overlay of the conversion layer (dry overlay of the treatment solution) is shown in Table 1. Subsequently, the surfaces of the conversion-coated test panels were examined. The dry coverage of the conversion coating was determined by RFA and the test panels were measured in the cyclic voltammetry to the To determine electron transfer barrier. Measured here was the current density at a potential of -770 mV. This is characteristic of the oxidation of the iron into its divalent form. The higher the reading, the higher the oxidizability. The results of the determination of the dry coverage and the cyclic voltammetry are shown in Table 1 .

The measured values of the cyclic voltammetry of Table 1 show relatively high values in the case of conversion layers of hexafluorotitanate, which indicates permeability of the layer. The conversion layers, which contain phosphates (zinc phosphate, iron phosphate), show consistently low measured values, which suggests a more covering and denser layer. In terms of oxidability, the phosphate-containing conversion layers therefore have better properties and in particular a higher corrosion resistance. The combination of hexafluorotitanate or hexafluorotitanic acid with zinc phosphate shows surprisingly good results in terms of zyklovoltammetrischen measurements (10 uA / cm ³ - 50 uA / cm ³ ). These values are in the range of complex, commercially available means for producing conversion coatings on metals. The positive properties of the titanium-containing conversion layers and of the phosphate-containing conversion layers can be combined if the aqueous treatment solution is produced from a mixture of hexafluorotitanate or hexafluorotitanic acid and zinc phosphate and / or iron phosphate with water as solvent, in particular with proportions by weight for the hexafluorotitanic acid of 1 to 10%. and for the zinc phosphate and / or iron phosphate of (in total) 1 to 10%. Phosphoric acid may also be added to this preferred mixture, for example in a proportion by weight of from 1 to 10%. The addition of phosphoric acid has the advantage that the zinc phosphate can be solved with it.

Then four different coatings (gold lacquer AN 101 597 with a run of 5 g / m ² were applied to the dried conversion layers; gold lacquer BPA ni Metlac 816,714 with a run of 5 g / m ^2; gold lacquer GL 300 MF with a run of 5 g / m ² , white varnish BPA ni Valspar R 1016 with an application of 15 g / m ² ) and the coated test panels were subjected to stress tests (forming and sterilization) and tested with the crosshatch test and the Erichsen graduation to evaluate the paint adhesion. A point rating system was used in which, depending on the quality of the paint adhesion, points from 0 (no adhesion) to 7 (optimal adhesion) have been awarded. The points that resulted for a conversion layer for the different paints were added and the sum of this addition is listed in Table 2 . The larger the sum value, the better the adhesion of the respective conversion layer for organic paints.

From Table 2 it can be seen that the conversion layers of hexafluorotitanate show the best results in terms of paint adhesion, with the adhesion increasing with increasing circulation. In the case of the conversion layers with phosphates (zinc phosphate, iron phosphate) it was found that lower runs tend to be better for paint adhesion and that zinc phosphate has better adhesion to iron phosphate with the same coverage. Accordingly, zinc has a positive influence on paint adhesion. Zinc may be present in an edition which corresponds to any of the aforementioned circulation areas, if the conversion layer contains the component zinc phosphate. Conversion layers having a weight fraction of from 1% to 5% of the zinc (based on the total amount of the conversion layer), preferably from 2 to 4% by weight, of zinc have proved to be particularly advantageous.

Lacquer adhesion results were compared with comparative samples of conventional tin-free steel sheets (ECCS and TFS) and with steel sheets coated with the commercially available Henkel "Bonderite®" agent. The conventional tin-free steel sheets (ECCS or TFS) have a total score of 115 and the "Bonderite®" -coated steel sheets have achieved overall scores in the range of 88 to 118, depending on the edition.

Comparative tests with various runs (basis weight) of the conversion layers have shown that the conversion coating of hexafluorotitanate gives good results up to an application of about 50 mg / m ² (based on titanium). A preferred range of the (titanium-related) edition of the conversion layer is therefore in the range of 1 to 50 mg / m ² , more preferably 3 to 40 mg / m ² , in particular 10 to 40 mg / m ² or even 20 to 40 mg / m ² or 15 to 30 mg / m ² .

In the case of the phosphate coating, good results are achieved up to a circulation of about 500 mg / m ² (based on the PO ₄ phosphate ion). A preferred range of the conversion of the conversion layer based on phosphate (PO ₄ ) is therefore in the region of 10 to 500 mg / m ² , more preferably 20 to 400 mg / m ² , in particular 50 to 300 mg / m ² , or else 100 to 250 mg / m ² or 150 to 300 mg / m ² .

In a further test, the formability of the painted sample sheets was investigated. For this purpose, the coated sample plates were formed by deep drawing to β-2 wells. It has been shown that even at high conversions, the conversion layers of hexafluorotitanate (hexafluorotitanic acid) are the most advantageous. However, it has been shown that the titanium-containing conversion layers with coating coverings> 40 mg / m ² do not give good results in the forming test, which is why coating runs of less than 40 mg / m ^{2 are} preferred for the titanium-containing conversion layers.

Studies were also carried out in which the conversion-coated test panels were coated with films (instead of a coating). After the deep-drawing of standard cups from the film-coated test panels, investigations were carried out with regard to film detachment.

The results show for each of the treatment solutions according to the invention, after short-term thermal aftertreatment, very good adhesion values, which are equivalent to those of the commercial complex conversion agents with organic substances.

Overall, the results of the investigations show that complex treatment solutions for producing conversion coatings on steel sheets containing organic substances (such as polymers and organic film formers) and particulate organic compounds with particle sizes greater than 50 nm are not required to provide adequate corrosion resistance to achieve good adhesion for organic paints and plastic films. Purely inorganic, simpler in composition, limited to the active ingredients and therefore more cost-effective treatment solutions according to the invention lead to comparable results, which are also quite comparable to conventional chromium-containing conversion layers on steel sheets.

It can be found within the scope of the invention that a coating with the active component titanium in the range of titanium deposits of 1 mg / m ² to 50 mg / m ² , preferably in the range of 10 mg / m ² to 40 mg / m ² gives good results. In the phosphate-containing conversion layers according to the invention, the element zinc has a positive effect on the properties and shows good results up to a zinc concentration of 5%.

The process according to the invention can be carried out without major installation effort into an existing coating installation, e.g. be integrated into a coil coating plant for the production of ECCS (or TFS). The belt speed in such belt coating systems is typically 80-600 m / min.

The inventive method has the advantages of a chromium-free, on inorganic components based and thus environmentally friendly and not harmful to health and very inexpensive conversion coating on steel sheets. The steel sheets treated by the method according to the invention are outstandingly 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. The black plates coated according to the invention with a conversion layer (cold-rolled steel plates without metal coating) are comparable with tinplate in terms of their corrosion resistance and have similarly good adhesion properties for organic lacquers and plastic coatings (for example of PP or PET), such as the tin-free steel sheets (TFS or ECCS ). <b> Table 1 </ b> No. effective component Concentration (% by weight) solvent Circulation (mg / m ² ) Cyclic voltammetry (μA / cm ² ) 1st cycle / 2nd cycle 1 hexafluorotitanic 1.0 water 5.0 118.8 2 hexafluorotitanic 3.0 water 12.0 93.0 3 hexafluorotitanic 5.0 water 13.0 131.4 4 hexafluorotitanic 7.0 water 28.0 114.0 5 hexafluorotitanic 10.0 water 39.0 154.0 6 zinc phosphate 1.0 water 120 12.6 Phosphoric acid (85%) 1.4 7 zinc phosphate 3.0 water 205 15.2 Phosphoric acid (85%) 2.3 8th zinc phosphate 5.0 water 383 21.0 Phosphoric acid (85%) 3.2 9 zinc phosphate 7.0 water 417 10.7 Phosphoric acid (85%) 4.1 10 zinc phosphate 10.0 water 592 7.7 Phosphoric acid (85%) 5.5 11 iron phosphate 1.0 water 348 24.5 Phosphoric acid (85%) 4.5 12 iron phosphate 3.0 water 583 18.7 Phosphoric acid (85%) 5.7 13 iron phosphate 5.0 water 671 24.2 Phosphoric acid (85%) 6.9 14 iron phosphate 7.0 water 968 14.5 Phosphoric acid (85%) 8.1 15 iron phosphate 10.0 water 1153 57.6 Phosphoric acid (85%) 9.9 16 hexafluorotitanic 1.0 water 52.0 zinc phosphate 2.0 phosphoric acid 3.0 17 hexafluorotitanic 1.0 water 52.4 17.2 / 38.0 zinc phosphate 2.5 phosphoric acid 1.0 No. effective component Concentration (% by weight) solvent Circulation (mg / m ² ) Total score paint adhesion 1 hexafluorotitanic 1.0 water 5.0 115 2 hexafluorotitanic 3.0 water 12.0 116 3 hexafluorotitanic 5.0 water 13.0 118 4 hexafluorotitanic 7.0 water 28.0 120 5 hexafluorotitanic 10.0 water 39.0 130 6 zinc phosphate 1.0 water 120 109 Phosphoric acid (85%) 1.4 7 zinc phosphate 3.0 water 205 90 Phosphoric acid (85%) 2.3 8th zinc phosphate 5.0 water 383 110 Phosphoric acid (85%) 3.2 9 zinc phosphate 7.0 water 417 65 Phosphoric acid (85%) 4.1 10 zinc phosphate 10.0 water 592 77 Phosphoric acid (85%) 5.5 11 iron phosphate 1.0 water 348 88 Phosphoric acid (85%) 4.5 12 iron phosphate 3.0 water 583 86 Phosphoric acid (85%) 5.7 13 iron phosphate 5.0 water 671 78 Phosphoric acid (85%) 6.9 14 iron phosphate 7.0 water 968 98 Phosphoric acid (85%) 8.1 15 iron phosphate 10.0 water 1153 83 Phosphoric acid (85%) 9.9 16 hexafluorotitanic 1.0 water 52.0 zinc phosphate 2.0 phosphoric acid 3.0 17 hexafluorotitanic 1.0 water 52.4 87 zinc phosphate 2.5 phosphoric acid 1.0

Claims (12)

Steel sheet having a conversion layer on at least one surface of the steel sheet, the conversion layer containing at least one of the following components: i) hexafluorotitanate, ii) zinc phosphate and / or iron phosphate, iii) phosphoric acid, with the proviso that the components i), ii) and iii) each contain no organic constituents. Steel sheet according to claim 1, wherein the conversion layer consists of one of the following components or a mixture of these components: i) hexafluorotitanate, ii) zinc phosphate and / or iron phosphate, iii) phosphoric acid, with the proviso that the components i), ii) and iii) each contain no organic constituents. Steel sheet according to claim 1 or 2, wherein the conversion layer, an organic paint and / or a plastic film is applied. Steel sheet according to one of the preceding claims, wherein the conversion layer contains phosphate ions. Steel sheet according to one of the preceding claims, wherein the coating of hexafluorotitanate in the conversion layer based on titanium in the range of 1 mg / m ² to 50 mg / m ² , preferably in the range of 10 mg / m ² to 40 mg / m ² , Steel sheet according to one of the preceding claims, wherein the phosphate coating in the conversion layer, based on phosphate ions, is in the range from 10 mg / m ² to 1000 mg / m ² , preferably in the range from 100 mg / m ² to 400 mg / m ² , A method of making a conversion coated steel sheet, comprising the following steps: a) providing a steel sheet, in particular in the form of a steel strip; b) cathodic degreasing of at least one surface of the steel sheet; c) applying a wet film of a conversion layer to the degreased surface of the steel sheet, wherein the wet film of the conversion layer is formed from components dissolved in water and the components are selected from: i) hexafluorotitanate, ii) zinc phosphate and / or iron phosphate, iii) phosphoric acid, and iv) a mixture of any of i) to iii), with the proviso that the components do not contain organic substances; d) drying of the wet film of the conversion layer. The method of claim 7, wherein an organic paint and / or a plastic film is applied to the dried conversion layer. A method according to claim 7 or 8, wherein after the cathodic degreasing, the degreased surface of the steel sheet is anodically polarized in an alkaline electrolyte. A treatment agent for applying a conversion layer on a steel sheet, wherein the treatment agent comprises water and at least one component selected from i) hexafluorotitanate, ii) zinc phosphate and / or iron phosphate, iii) phosphoric acid and iv) a mixture of any of i) to iii), with the proviso that the components i), ii) and iii) are free of organic constituents. A treating agent according to claim 10, wherein the treating agent is water and a mixture of hexafluorotitanate, zinc phosphate and / or iron phosphate and phosphoric acid. The treating agent according to claim 10, wherein the treating agent is water and one of the following components or a mixture of these components: i) hexafluorotitanate, ii) zinc phosphate and / or iron phosphate, iii) phosphoric acid, with the proviso that the components i), ii) and iii) each contain no organic constituents.