WO2009112452A2

WO2009112452A2 - Continuous method for treating the surface of metal strips

Info

Publication number: WO2009112452A2
Application number: PCT/EP2009/052716
Authority: WO
Inventors: Alexsandro Berger; Walter Bertkau; Mirjam Herrlich-Loos; Bernd Laubusch; Jessica Neumann; Bernd Strubel; Guido Vandermeulen; Helmut Witteler
Original assignee: Basf Se
Priority date: 2008-03-12
Filing date: 2009-03-09
Publication date: 2009-09-17
Also published as: WO2009112452A3

Abstract

Disclosed is a continuous method for treating the surface of metal strips. In said method, a surface property-modifying layer having a maximum thickness of 3 μm is applied by means of a device comprising at least one Fourier transform IR spectrometer which faces a coated side of the strip, operates using reflection geometry, and records IR spectroscopic measurement data of the applied surface property-modifying layer while the metal strip advances in order to characterize the surface.

Description

Continuous process for the surface treatment of metal strips

description

The present invention relates to a continuous process for the surface treatment of metal strips, wherein a coating layer is applied with a dry film thickness of less than 3 microns, wherein the device used for applying with at least one, a coated side of the tape facing, working in reflection geometry Fourier transform IR spectrometer is equipped with the IR-spectroscopic measured data for characterizing the surface of the applied coating layer while the metal strip is running.

The steel strips are usually protected by suitable measures against corrosion. These are generally multilevel processes. In a first step, the steel strips are usually coated with zinc or zinc alloys. The effect of zinc is based on the one hand, that it is less noble than steel and therefore first itself corroded. The steel surface remains intact as long as it is still covered with zinc throughout. Furthermore, in the presence of atmospheric oxygen on the surface of Zn or Zn alloys, a thin oxide layer is formed which more or less slows the corrosive attack on the underlying metal, depending on the external conditions.

In order to enhance the protective effect of such an oxide layer, the Zn surfaces are usually subjected to an additional passivation treatment. In the course of such treatment, a part of the metal to be protected dissolves, and is at least partially incorporated into a film on the metal surface. Instead of the term "passivation layer", the terms "conversion layer", "aftertreatment layer" or "pretreatment layer" are also used interchangeably.

It is known to perform such a passivation by treating the galvanized steel surface with acidic Cr (VI) and / or Cr (III) solutions. Increasingly, chromium-free formulations are also used for this purpose, e.g. phosphate-containing formulations or else formulations which contain various polymers.

An important class of polymers used in passivation formulations are acidic water-soluble polymers such as polyacrylic acid or copolymers of acrylic acid with other monomers, especially other acidic monomers such as vinyl phosphonic acid, maleic acid or itaconic acid. The use of such polymers for passivation is disclosed, for example, in WO 2004/074372, WO 2005/042801, WO 2006/021308, 2006/021309, WO 2006/134116, WO 2006/1341 17 or WO 2006/134118. But it is also known that polymer use with N-containing groups, such as polymers containing vinylimidazole, as disclosed for example by WO 2004/81128.

Passivation layers are usually very thin. The dry film thickness of passivation layers is usually not more than 3 μm; In modern Passivvierungsverfahren a dry film thickness is sought below 1 micron, for example, 0.01 to 0.4 microns. For quality control and control of the process, the layer thickness must be determined.

This control is usually carried out batchwise, d. H. During operation, a sample is cut out of the moving metal strip and examined in the laboratory by wet chemical or spectroscopic methods. This method is unsatisfactory because it is time consuming and does not allow a sufficiently fast response to changes in tape quality.

It is also known to use X-ray fluorescence analysis for continuous monitoring of the moving metal strip in the course of a surface treatment. Although this makes it possible to check, the X-ray fluorescence analysis can only be used to determine a number of conducting elements and can not be used to determine the deviation of the chemical composition with an otherwise identical conducting element concentration. Thus, for example, it is not possible to differentiate between the coating of the surface with chromate compounds and the coating with chromium (III) salts by means of X-ray fluorescence methods. Further, X-ray fluorescence methods can not be used to determine thin films with organic coating materials such as oils and polymers since they do not react to them. In addition, X-ray fluorescence analysis does not work while the tape is running, but the tape must be stopped for measurement. Other classical layer thickness measuring methods do not have a sufficiently high sensitivity to quantitatively describe layer thicknesses of less than 1000 nm.

It is known to use IR spectroscopic methods in the course of the production of metal sheets and metal strips.

EP 488 726 A2 discloses a method of silicon steel sheets in which the surface finish of the silicon steel is defined by the intensity of infrared absorption bands. It is not a continuous process.

DE 199 41 734 B4 discloses a continuous process for process control in the pickling of steel strip. Pickling is understood by one skilled in the art to be the removal of oxides and other contaminants from metallic surfaces. In this case, by intensity analysis of reflected IR radiation, a determination of the degree of scaling the metal surface and controlled depending on the measured values of the pickling process.

DE 199 41 600 C2 discloses a method for process control and process optimization during hot rolling of steel, in which the electromagnetic radiation emitted by the hot metal is detected and evaluated online as a spectrum, and wherein crystallographic transformations of the metal, which take place at certain temperatures, evaluated become.

IR spectroscopic methods for the continuous control of the surface treatment of metal strips with thin tempering layers, in particular for the continuous control of the passivation of metal strips, have not been described hitherto.

The object of the invention was to provide a continuous process for the surface treatment of metal strips, in particular for passivating metal strips, in which a continuous quality control is performed with the metal strip running.

Accordingly, there has been found a process for the continuous surface treatment of a metal strip with a liquid formulation (F), in which a metal strip is moved longitudinally through a metal strip surface treatment apparatus comprising at least

• a device (3) for applying the formulation (F) and

Comprising a drying station (5),

and wherein the formulation (F) comprises at least one solvent and coating-forming components, the formulation (F) is applied to the metal strip by means of the device (3), the solvents are at least partially removed by means of the drying station, wherein the amount of the formulation to be applied such that a coating layer with a dry film thickness of less than 3 μm is formed on the metal surface, and furthermore wherein the device used, viewed in the direction of the tape, faces the drying station (5) with at least one, one coated side of the tape, working in reflection geometry

Fourier transform IR spectrometer (6) is equipped with the IR-spectroscopic data recorded by the applied coating layer while the metal strip is running to characterize the surface.

In a preferred embodiment of the invention, the surface treatment is a passivation. Particularly preferred is a Acid passivation using at least one acid group-comprising polymer.

List of pictures:

Fig. 1: Schematic representation of essential elements of the method according to the invention, one-sided application

Fig. 2: Schematic representation of essential elements of the method according to the invention, one-sided application, other application

Fig. 3: Schematic representation of essential elements of the method according to the invention, two-sided application

Fig. 4: Schematic representation of essential elements of the method according to the invention, one-sided application, other application, with additional support role

Fig. 5: Schematic representation of essential elements of the method according to the invention, two-sided application, with additional support role

Fig. 6 Fourier transform IR spectra of a passivation layer on steel obtained with three different formulations, each containing polyacrylic acid and nitric acid.

More specifically, the following is to be accomplished for the invention:

In the method according to the invention for the continuous surface treatment of metal strips, a liquid formulation (F) comprising at least one solvent and coating-forming components is applied to the surface of a metal strip. Here, a non-metallic coating layer is obtained on the metal surface, which has a dry film thickness of less than 3 microns.

The term "temper layer" is intended to encompass all types of thin non-metallic layers of said thickness with which the surface of metal strips can be treated by treatment with suitable formulations to alter their properties, particularly with regard to subsequent processing steps such as application Of course, the term "non-metallic" should not exclude that a coating layer may contain metal ions or metal compounds, for example metal oxides, this is only intended to delimit the coating of the Bandes done with metals or metal alloys themselves, such as the galvanizing of the strip. Preferably, tempering layers comprise at least one organic component. Characteristic of tempering layers is that they are applied directly to the metal surface.

Examples of non-metallic tempering layers include temporary or permanent corrosion protection layers, in particular passivation layers, adhesive layers or wax layers, which can be applied, for example, to improve the formability, phosphatings, chromating, conversion layers or even reactive coatings in which cations are dissolved out of the metal and become part of the layer.

The method according to the invention is preferably a passivation, and the coating layer is accordingly a passivation layer.

The metal strips used for the process can in principle be all types of metal strips. Depending on the intended use, the metal strips used may have a thickness of 0.05 mm to 5 mm, preferably 0.3 to 3 mm, a width of 0.5 to 2.5 m and a length of several hundred meters. Preferably, it is bands of steel, iron, zinc, tin, aluminum, copper or alloys thereof, wherein the bands may also have a metallic coating, for example of tin, zinc, aluminum, nickel, preferably zinc, aluminum or alloys thereof ,

In a preferred embodiment of the invention, the metal strip used is a steel strip, more preferably a galvanized steel strip. These may be hot-dip galvanized or electrolytically galvanized steel strips. Galvanized steel strips are commercially available for a wide variety of applications. The person skilled in the art selects a suitable steel strip depending on the intended use.

Of course, the term "galvanized" also covers coatings with Zn alloys Zn alloys for coating steel are known to the person skilled in the art

Amount of alloy components. Typical constituents of zinc alloys include in particular Al, Mg, Pb, Si, Mg, Sn, Cu or Cd, preferably Al or Mg. It may also be Al-Zn alloys in which Al and Zn in approximately the same Quantity are available. The coatings may be substantially homogeneous coatings or even coatings having concentration gradients. Further preferably, it may be Zn-Mg alloys. This may be steel coated with a Zn-Mg alloy, For example, galvanized steel, or it may be galvanized steel, which was additionally vapor-deposited with Mg. As a result, a surface Zn / Mg alloy can arise.

The bands can be galvanized on one or both sides. For both sides galvanized bands both sides or even one side can be treated by the method according to the invention.

To carry out the method according to the invention, a coil coating system is used. Figures 1 to 3 show schematically different embodiments of the essential components of the coil coating plant. Not shown are the devices for unwinding the raw steel strip from the roll, the device for winding the coated strip and the drive device for the strip. Of course, the strip coater can optionally also include other conventional components, such as a tempering station or cleaning stations. Furthermore, the coil coating plant can be part of an entire production line, for example, in which first a metal strip is galvanized, then provided with a coating layer by means of the method according to the invention and optionally subsequently varnished. The metal strips can be driven through the system, for example at a speed of 20 to 300 m / s, preferably 50 to 150 m / s.

For carrying out the method according to the invention, a formulation (F) is applied to the metal strip (1) which moves in the running direction (2) by means of a device (3). For example, the formulation may be sprayed onto the belt by means of a spray device (# (3) in Fig. 1). It can of course also be applied to an applicator roll or a combination of several rolls, which in turn transfer the formulation to the belt. The application to an applicator roll can be done for example by spraying, dipping or pouring.

In general, the system also includes a device for separating excess formulation and / or smoothing the coating on the metal strip.

This may, for example, be a squeegee device, for example a doctor blade. In a preferred embodiment, these are two oppositely arranged rollers (4) and (4 '). Between the two rollers (4), (4 ') remains a gap, which is adjustable in width. For this purpose, one or both rollers may be provided with a corresponding mechanism for adjusting the roller position. To carry out the method, the metal strip is moved in its longitudinal direction through the adjustable gap between the rollers (4), (4 '). The rollers rotate in the direction (2) of the steel strip. The application of the formulation (F) on the metal strip can also be carried out indirectly, by applying the formulation with an applicator (3) first on one of the rollers (4) or on both rollers (4), (4 ') and from the rollers transfers to the metal band. Optionally, excess formulation may be removed from the rolls (4), (4 ') by means of suitable doctoring devices (7) and (7'), respectively. This embodiment is shown by way of example in Figures 2 and 3. Of course, other embodiments of the applicator device (3) are also possible, for example those which have a combination of several rollers.

Finally, the solvent contained in the formulation (F) is completely or at least partially removed by means of a drying device (6) arranged behind the device (4) in the running direction (2) of the belt behind the application device (3) or, if present. The reaction time of the formulation on the metal surface is determined by the distance between the application device (3) and the drying device (5) taking into account the belt speed.

The drying device (5) can be, for example, a circulating air dryer or an IR dryer. The drying temperature is set by the skilled person depending on the formulation used (F) and the desired properties of the layer. Proves itself has a temperature of 25 to 95 ° C and preferably 30 to 80 ⁰ C, measured as "peak metal temperature". The temperature of the recirculating air in a convection dryer can in this case be of course also be higher.

After passing through the drying device (5), a dried coating layer remains on the metal strip, whereby the term "dried" does not of course exclude that even small amounts, in particular traces of the solvent, can be present in the layer on the metal surface has a dry film thickness of less than 3 .mu.m, preferably less than 2 .mu.m, in particular layers which have a dry film thickness of 1 nm to 1000 nm, preferably 5 nm to 500 nm and particularly preferably 10 nm to 300 nm exhibit.

The dry layer thickness can be controlled by the person skilled in the art by means of measures known in principle, for example via the applied amount of the formulation (F) and its concentration. Further control possibilities consist in the suitable setting of the device (4), for example the distance of the rollers from one another, if (4) is a pair of rollers (4), (4 '), or the distance of a doctor blade from the surface of the band metal if (4) is a doctor blade.

The selected layer thickness depends in each case on the desired properties of the layer. According to the invention, the apparatus used, viewed in the direction of the belt, after the drying station (5) comprises at least one Fourier transform IR spectrometer (6), with which infrared spectroscopic measured data for characterizing the surface of the applied tempering layer while the metal strip is running can be recorded. The Fourier Transform IR spectrometer operates in reflection geometry and faces a coated side of the belt. This can only be a spectrometer if only one side of the metal strip is coated or two spectrometers if both the top and the bottom of the strip is coated. This is shown comparatively in Figures 2 and 3. It is of course also possible to use in each case a plurality of spectrometers per page, for example, several spectrometers distributed over the width of the metal strip.

The Fourier transform IR spectrometer is equipped with suitable mirrors, with which the measuring beam is directed by the IR transmitter onto the metal surface and the IR radiation reflected from the surface is transmitted to the IR detector.

The measuring spot on the coated with the coating layer metal surface should normally be a diameter of a few millimeters, for example 5 to 10 mm.

The distance of the Fourier Transform IR spectrometer from the metal surface should be as small as possible. Has proven to be a distance from the exit of the beam from the device to the metal surface of less than 100 mm, preferably 8 to 40 mm and more preferably 7 to 15 mm.

In a preferred embodiment of the invention, at least one Fourier transform IR spectrometer is arranged so that the distance of the spectrometer to the strip surface is variable. Thus, the spectrometer can be moved as close to the metal surface for measuring operation, while it can be moved away in situations where it is not needed, for example, when the system from the metal surface. The details of a suitable device for changing the distance are not important here.

In a further preferred embodiment, the metal strip is supported at or near the point of IR measurement with at least one additional support roller or deflection roller (8). Metal strips in a strip coater can make flapping motions that could interfere with IR measurement. By a support or deflection roller (8) such flutter movements can be suppressed or at least mitigated. The term "support roller" is intended to mean a roller which supports a straight, in particular horizontally running, metal band without the role changes the direction of the tape, a pulley simultaneously changes the direction of the tape more or less strong. This embodiment of the invention is shown by way of example in FIGS. 4 and 5. The support or deflecting roller (8) is located on the side of the metal strip facing away from the IR measurement, for example directly below the IR measurement. However, such an arrangement is not mandatory, it is sufficient that the roller is arranged in such proximity to the IR measurement that it can effectively suppress or at least mitigate fluttering. In general, the lower the distance, the better the results obtained. As a rule, the distance of the supporting or deflecting roller (8) to the measuring point should not be more than 4 m, preferably not more than 1 m.

The IR measurement can be done in the near infrared (NIR, 13160 - 4000 cm- ¹ ), middle infrared (MIR, 4000 - 200 cm- ¹ ) or far-infrared (FIR, 200 - 10 cm- ¹ ). The choice of the wavelength depends on the type of the coating layer to be applied. Preferably, a Fourier transform IR spectrometer is used which operates in the range of 200 to 4000 cm ^-1 , ie in the MIR range.

By means of the measuring device described, IR spectra of the applied tempering layer can be recorded while the metal strip is running. The spectra can be qualitatively and quantitatively evaluated and the data obtained can be used to control the coating process.

The IR measurement can be used in particular for measuring and controlling the layer thickness. The thicker the coating layer applied, the more the layer absorbs and, accordingly, the proportion of reflected IR radiation registered by the Fourier transform IR spectrometer.

The recording of the IR spectra can in each case take place in the entire possible spectral range of the Fourier transform IR spectrometer, or else only in a subarea thereof. For the purpose of measurement and / or evaluation, the person skilled in the art selects one or more suitable IR-active bands of the applied tempering layer. The measurement data determined by the Fourier transform IR spectrometer can be converted into a quality value in a computer. The quality value can be obtained, for example, by comparing the measurement data with a calibration curve, the quality value increasing or decreasing with the layer thickness. The calibration curve can be obtained by applying the formulation used for surface treatment (F) in different layer thicknesses on steel sheets, each measuring the FT-IR spectra, and determines the respective layer thickness with a different measurement method. Furthermore, the position of the IR bands can also be included in the quality value. It is known that certain IR bands can shift in the IR spectrum depending on the chemical environment. For example, reference is made to a -COOH group whose IR Absorption bands, depending on whether they are present as free acid, as salt or complexed, lie at different wavenumbers. It is thus possible to make a statement about the measurement of the IR absorption, of which the -COOH group is still incorporated in the desired manner in the tempering layer. Of course, several different quality values can also be determined and used for the control.

In a preferred embodiment of the invention, the amount of formulation (F) to be applied is controlled as a function of the quality value.

In a further preferred embodiment of the invention, the composition of the formulation (F) to be applied is controlled as a function of the quality value. For example, the total concentration of the formulation (F) can be controlled or the concentration of individual components in the formulation (F).

Advantageously, for this purpose, the IR spectroscopic measurement of the coating layer can also be combined with an IR spectroscopic monitoring of the composition of the formulation (F). From the formulation can be recorded, for example by means of ATR probes during operation IR spectra. For example, the ATR probe can be immersed in the storage tank containing the formulation.

The evaluation of the spectra and possibly the control of the system can be done manually.

In a preferred embodiment of the invention, the qualitative and quantitative evaluation of the spectra and optionally the direct control of the system can be carried out automatically via a computer. The intensity of the band can be determined in a manner known in principle by means of integration. Computer-assisted methods for such evaluations are known in principle to the person skilled in the art. The arithmetic unit can be mounted directly on the site of the system, but it can of course also be a remote control, for example via the Internet.

Details of the IR measurement depend on the type of the coating layer or formulation (F).

Formulations (F)

The liquid formulations (F) used comprise at least one solvent and coating-forming components. They are preferably aqueous formulations. As a solvent, the formulation (F) preferably comprises only water. It may also comprise water-miscible organic solvents in small quantities. Examples include monoalcohols such as methanol, ethanol or propanol, higher alcohols such as ethylene glycol or polyether polyols, ether alcohols such as butyl glycol or methoxypropanol and N-methylpyrrolidone. As a rule, however, the amount of water is at least 80% by weight, preferably at least 90% by weight and very particularly preferably at least 95% by weight. The data refer to the total amount of all solvents.

The coating-forming components may be, for example, dissolved metal ions or metal compounds which are deposited, for example, on the surface in the form of oxides and / or hydroxides, in particular compounds of the elements Zn, Mg, Al, Cr, Ni, Co, Mo, Mn, W, Si, Zr or Ti. The coating-forming components may furthermore be organic components. Examples of organic components include waxes or oils, and in particular water-soluble or at least water-dispersible polymers.

In a preferred embodiment of the invention, the formulation (F) comprises at least one component selected from the following group of components:

1. Hexafluorometallate [MFβ] ^{2 "} where M = Ti, Si, Zr.

2. Oxometalates of aluminum, molybdenum, chromium, tungsten and manganese.

3. Salts comprising the cations of Ca, Mg, Zn, Ni, Fe, Ni, Cr. 4. Salts comprising the anions NO ₃ ^" , NO ₂ ^" , PO ₄ ^{3 "} , HPO ₄ ^2" , H ₂ PO ₄ -, SO ₄ ^{2 "} , SO ₃ ^" ,

CO ₃ ² -, HCO ₃ - or CH ₃ COO.

5. rolling and corrosion protection oils.

6. waxes.

7. organic film formers. 8. Polymers and copolymers obtainable from at least one of the following

components

C3-, C4- or C5-carboxylic acids having one or two double bonds, in particular acrylic acid,

• acrylic acid esters, • unsaturated sulfonic acids, phosphonic acids, phosphonic esters,

Vinylpyrrolidone, vinylimidazole, vinyl acetate, acrylamide and N-substituted derivatives of acrylamide,

• ethyleneimine.

The formulations (F) may be, for example, aqueous metalworking fluids having a pH> 7 which, in addition to water, contain at least oils and / or waxes and corrosion inhibitors. Such formulations are used, for example, to reduce the coefficients of friction during deformation.

In a preferred embodiment of the invention, the surface treatment is a passivation, preferably the passivation of galvanized steel strips. Passivation formulations are known in principle to a person skilled in the art.

In one embodiment of the invention, it can be a phosphate passivation, in which an aqueous formulation (F) having a pH <5 is used, wherein the formulation comprises not only water but also at least phosphoric acid and / or phosphate and at least one metal ion. The metal ions may preferably be at least one metal ion selected from the group of Cr ³⁺ , Zn ²⁺ , Mg ²⁺ , Ca ²⁺ or Al ³⁺ , preferably Cr ³⁺ , Zn ²⁺ , Mg ²⁺ , Ca ²⁺ or Al ³⁺ act.

In a preferred embodiment of the invention, an aqueous, acidic formulation (F) having a pH <5, which comprises at least one water-soluble or water-dispersible polymer, is used for passivation. Preference is given to using water-soluble polymers.

The acidic pH can be achieved because the polymer itself contains acidic groups in sufficient quantities, or else the formulation (F) used can contain, in addition to the water-soluble or water-dispersible polymers, inorganic or organic acids or mixtures thereof. The choice of such acid is not limited, provided that there are no adverse effects along with the other components of the formulation. The skilled person makes a corresponding selection. Examples of suitable acids include phosphoric acid, phosphonic acid or organic phosphonic acids such as 1-hydroxyethane-1, 1-diphosphonic acid (HEDP), 2-phosphonobutane-1, 2,4-tricarboxylic acid (PBTC), aminotri (methylene phosphonic acid ) (ATMP), ethylenediaminetetra (methylenephosphonic acid) (EDTMP) or diethylenetriaminepenta (methylenephosphonic acid) (DTPMP), sulfonic acids such as methanesulfonic acid, amidosulfonic acid, p-toluenesulfonic acid, m-nitrobenzenesulfonic acid and derivatives thereof, nitric acid, formic acid, acetic acid. It is also possible in principle to use unsaturated acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, vinylphosphonic acid, acrylamidopropylsulfonic acid. Phosphorus-containing acids such as H 3 PO 4, phosphonic acid are preferably the organic phosphonic acids mentioned, HNO 3 or methanesulfonic acid. It may preferably be H3PO4 or another phosphorus-containing acid.

The preferred formulation (F) used for passivation generally comprises 10 to 35% by weight, preferably 12 to 35% by weight, particularly preferably 14 to 32% by weight. and most preferably from 16 to 28% by weight of the water-soluble polymers, based on the amount of all components of the formulation (ie including the solvents).

The formulation (F) preferably used for passivation has a pH of not more than 5, in particular a pH of 0.5 to 5, preferably 0.8 to 3.5. The pH of the preparation naturally depends on the type and concentration of the polymers used. It can still be influenced by other basic or acidic components in the formulation.

In addition to the polymer and optionally the acid, the passivation formulation (F) may optionally comprise metal ions or metal compounds.

The metal ions may be at least one metal ion selected from the group of Cr, Zn, Mg, Ca, Al, Mn, Mo, Co, Ni, Fe, Ti, Si, Zr, preferably selected from the group of Zn, Mg, Ca or AI act. The preparation next to it preferably does not comprise any further metal ions. The ions may be present as hydrated metal ions, but they may be in the form of dissolved compounds, for example as complex compounds. In particular, the ions may have complex bonds to the acidic groups of the polymer.

If present, the amount of metal ions in the group of Cr, Zn, Mg, Ca, Al, Mn, Mo, Co, Ni, Fe, Ti, Si, Zr is 0.01 wt% to 20 wt%, preferably 0 , 5 to 18 wt.% And particularly preferably 1 to 15 wt.%, In each case based on the total amount of all polymers X in the formulation.

The formulation may further comprise at least one dissolved phosphate ion. These can be all types of phosphate ions. For example, they may be orthophosphates or diphosphates. It is clear to the person skilled in the art that in aqueous solution, depending on the pH and concentration, there may be an equilibrium between the different dissociation stages of the ions. Furthermore, the formulation may include methanesulfonate ions.

If phosphate ions are present, the metal ions and phosphate ions can preferably be used in the form of soluble salts containing both ions. Examples of such compounds include Zn3 (PÜ4) 2, Zn ^ PO _4, Mg 3 (PO ₄₎ 2 or Ca (H2PO ₄₎ 2, or corresponding hydrates thereof.

The metal ions and phosphate ions can, however, also be added separately to one another. For example, the metal ions can be used in the form of the corresponding nitrates, alkanesulfonates or carboxylates, for example acetates, and the phosphates can be used in the form of phosphoric acid. It is also possible to use insoluble or sparingly soluble compounds, such as the corresponding carbonates, oxides, oxide hydrates or hydroxides, which are dissolved under the influence of acid.

Similarly, metal ions and methanesulfonate ions may be used together as metal salts of methanesulfonic acid such as Zn (CH 3 SO 3) 2, or else separately in the form of other metal salts and methanesulfonic acid.

The amount of phosphate ion and / or methane sulfonate ion in the formulation will be determined by those skilled in the art according to the desired properties of the formulation. If present, it is generally 0.01% by weight to 20% by weight, preferably 0.5 to 25% by weight, particularly preferably 1 to 25% by weight, in each case calculated as orthophosphoric acid and in each case based on the water-soluble polymers.

Optionally, the formulation may further contain at least one wax dispersed in the formulation. Of course, mixtures of different waxes can be used. The term "wax" here encompasses both the actual wax and any auxiliary agents which may be used to form a wax dispersion .Waxes for use in aqueous dispersions are known to the person skilled in the art and suitable choices are made Oxydated polyethylene waxes based on fluorinated polyethylene such as PTFE or other polymers based on C, H and F. The term "polyethylene" is also intended to include copolymers of ethylene and other monomers, especially other olefins such as propylene. Preferably, such ethylene copolymers comprise at least 65 weight percent ethylene. By the addition of waxes, the friction of the surface with the surface of the tools used for forming can be advantageously reduced.

The amount of optionally used waxes is determined by the skilled person depending on the desired properties of the passivation layer. As a rule, an amount of from 0.01 to 70% by weight, preferably from 0.5 to 25 and particularly preferably from 1 to 10% by weight, based in each case on the water-soluble polymers, has proven useful.

Other optional components for the formulation include surface-active compounds, corrosion inhibitors, complexing agents or typical electroplating agents.

The person skilled in the art will make an appropriate selection of the possible optional components as well as their quantities depending on the desired application. The amount of optional components besides water-soluble polymers should but as a rule not more than 20% by weight, preferably not more than 10% by weight and more preferably not more than 5% by weight, based on the polymers.

The formulations to be used according to the invention can be obtained by simply mixing the components. If waxes are used, they are preferably first dispersed separately in water and mixed as a dispersion with the other components. Such wax dispersions are also commercially available.

In a preferred embodiment of the invention, the water-soluble polymers are polymers X comprising acidic groups or polymers Y comprising basic groups.

Formulations with polymers X

The acidic polymers X preferably have at least 0.6 mol of acid groups / 100 g of the polymer. This quantity refers to the free acid groups. The polymers preferably have at least 0.9 mol of acid groups / 100 g, more preferably at least 1 mol / 100 g and very particularly preferably at least 1.2 mol / 100 g.

The acidic groups of the polymers X are generally selected from the group of carboxyl groups, sulfonic acid groups, phosphoric or phosphonic acid groups. Preference is given to carboxyl groups, phosphorus or phosphonic acid groups. The polymer X used preferably comprises at least COOH groups. With particular preference, the polymer X used is a copolymer of at least two different acid group-containing monomers.

When using the acidic polymers X, the acidity of the formulation used should be essentially caused by the acid groups of the polymer. The amount of additional acids in addition to the polymers X in the formulation should therefore generally not exceed 50% by weight with respect to the amount of all polymers X in the formulation together. Preferably, 30% by weight, particularly preferably 20% by weight and very particularly preferably 10% by weight, should not be exceeded. In a second, particularly preferred embodiment of the invention, no additional acids are present.

The acid groups of the polymer X should preferably be present as free acid groups. However, they can also be neutralized to a slight extent by means of bases, such as ammonia, amines, amino alcohols or alkali metal hydroxides. Such partial neutralization can be done for pH adjustment. But it can also inevitably result in the course of the production of the polymer. It For example, it is known to those skilled in the art that it may be necessary to neutralize some of the acid groups in the course of the preparation of polymers having high acid groups in order to force incorporation of the monomers into the polymer.

The degree of neutralization should not be too high, however, to ensure a good acid attack on the zinc surface. As a rule, therefore, not more than 25 mol% of the acid groups present in the polymer X should be neutralized, preferably not more than 20 mol% and particularly preferably not more than 12 mol%.

Homo- or copolymers X which comprise (meth) acrylic acid units are particularly preferably used for carrying out the invention.

In a particularly preferred embodiment of the invention, the polymer X is one or more water-soluble copolymers X1 of (meth) acrylic acid units (A) and different monoethylenically unsaturated monomers having acidic groups (B). Optionally, OH-containing (meth) acrylic acid esters (C) and / or further monomers (D) may also be present as structural units. In addition, no further monomers are present. The amount of (meth) acrylic acid (A) in the copolymer XI is from 30 to 90% by weight, preferably from 40 to 80% by weight and more preferably from 50 to 70% by weight, this information being based on the sum of all monomers in the polymer ,

The monomer (B) is at least one monoethylenically unsaturated monomer other than (A) but copolymerizable with (A) which has one or more acidic groups. Of course, several different monomers (B) can be used. The acidic groups in monomer (B) may preferably be a group selected from the group of carboxyl groups, phosphoric acid groups, phosphonic acid groups or sulfonic acid groups. It is preferably a group selected from the group of carboxyl groups, phosphoric acid groups or phosphonic acid groups. Examples of such monomers include crotonic acid, vinylacetic acid, C 1 -C ₄ monoesters of monoethylenically unsaturated dicarboxylic acids, styrenesulfonic acid, vinylsulfonic acid, allylsulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), vinylphosphonic acid, monovinyl phosphoric acid, maleic acid, fumaric acid or itaconic acid. The amount of monomers (B) in the copolymer X1 is 10 to 70 wt.%, Preferably 20 to 60 wt.%, And particularly preferably 30 to 50 wt.%, Each based on the sum of all monomers in the polymer.

In a preferred embodiment of the invention, the monomers (B) are monoethylenically unsaturated dicarboxylic acids having 4 to 7 carbon atoms (B1) and / or monoethylenically unsaturated phosphoric and / or phosphonic acids (B2). Examples of monomers (B1) include maleic acid, fumaric acid, methyl fumaric acid, methylmaleic acid, dimethylmaleic acid, methylenemalonic acid or itaconic acid. If appropriate, the monomers can also be used in the form of the corresponding cyclic anhydrides. Preference is given to maleic acid, fumaric acid and itaconic acid, particularly preferably maleic acid or maleic anhydride.

Examples of monomers (B2) include vinylphosphonic acid, phosphoric acid monovinyl ester, allylphosphonic acid, phosphoric acid monoallylester, 3-butenylphosphonic acid, mono (3-butenyl) phosphoric acid, (4-vinyloxybutyl) phosphoric acid, phosphonoxyethyl acrylate, methacrylic acid (phosphonoxyethyl) esters, mono (- 2-hydroxy-3-vinyloxypropyl) phosphoric acid, phosphoric acid mono- (1-phosphonoxymethyl-2-vinyloxy-ethyl) esters, phosphoric mono (3-allyloxy-2-hydroxypropyl) esters , Mono-2- (allylox-1-phosphonoxymethyl-ethyl) phosphoric acid, 2-hydroxy-4-vinyloxymethyl-1,3,2-dioxaphosphole, 2-hydroxy-4-allyloxymethyl-1,3,2-dioxaphosphole. Preference is given to vinylphosphonic acid, phosphoric acid monovinyl ester or allylphosphonic acid, particularly preferably vinylphosphonic acid.

In addition, the copolymer X1 may optionally contain at least one (meth) acrylic acid ester (C) containing OH groups. Preference is given to monohydroxy (meth) acrylates.

The monomers (C) are preferably at least one (meth) acrylic ester of the general formula H ² C =CHR ¹ -COOR ² , where R ^{1 is} in a manner known in principle to be H or methyl and R ^{2 is selected} from the group of R ² ^2a , R ^2b or R ^{2c is} selected.

The radicals R ^2a are radicals of the general formula - (R ³ -O-) _n -H. Here, n is a natural number from 2 to 40. Preferably, n is 2 to 20 and more preferably 2 to 10. The radicals R ³ are each independently of one another for a divalent, straight-chain or branched alkyl radical having 2 to

4 C atoms. Examples include in particular 1, 2-ethylene radicals, 1, 2-propylene radicals, 1, 2-butylene radicals and 1, 4-butylene radicals. Of course, it may also be mixtures of different radicals. It is preferably 1, 2-ethylene and / or 1, 2-propylene radicals. Particularly preferred are only 1, 2-ethylene radicals. Preference is furthermore given to radicals (R ^2a ) which have both 1,2-ethylene and 1,2-propylene radicals, the amount of the ethylene radicals being at least 50%, preferably at least 70% and particularly preferably at least 80%, based on the total number of all radicals R is ³ . Examples of R ^2a include -CH ₂ -CH ₂ -O-CH ₂ -CH ₂ -O-CH ₂ -CH ₃ , -CH ₂ -CH (CHS) -O-CH ₂ -CH (CH ₃ ) OH, -CH ₂ -CH ( CH ₃₎ - O-CH (CH ₃₎ -CH ₂ OH, - CH (CHs) -CH ₂ - 0 CH (CHs) -CH ₂ OH or -CH (CHs) -CH ₂ -O-CH ₂ - CH (CH ₃ ) OH. The radicals R ^2b are radicals of the general formula -R ⁴ - (OH) _m . Here, m is a natural number of 1 to 6, preferably 1 to 4, particularly preferably 1 to 3 and for example 1 or 2. The radical R ⁴ is an (m + 1) -qualified, straight-chain or branched alkyl radical 2 to 10 C-atoms, preferably 2 to 6 C-atoms and more preferably 2 to 4 C-atoms.

The alkyl radical is substituted with at least one OH group, with the proviso that no more than one OH group X per C atom is present in R ⁴ . Examples of suitable radicals R ^2b having OH groups include linear radicals of the general formula - (CH ₂ ) _m -OH, such as -CH ₂ -CH ₂ -OH, -CH ₂ -CH ₂ -CH ₂ -OH, -CH ₂ -CH ₂ -CH ₂ -CH ₂ -OH or -CH ₂ -CH ₂ - CH ₂ -CH ₂ -CH ₂ -CH ₂ -OH.

Particularly preferred radicals R ^2b for carrying out the invention are radicals selected from the group of -CH ₂ -CH ₂ -OH, -CH ₂ -CH ₂ -CH ₂ -OH, -CH ₂ -CH ₂ -CH ₂ -CH ₂ - OH, -CH ₂ -CH (CH ₃ ) -OH, -CH (CHs) -CH ₂ -OH or -CH ₂ -CH (OH) -CH ₂ -OH.

In a further preferred embodiment of the invention, at least one of the radicals R ^2b is a branched alkyl radical of the general formula - R ⁵ -CH (R ⁶ ) OH. Here, R ⁵ and R ⁶ each represent a linear or branched alkyl radical having 1 to 8 C atoms, preferably 1 to 6 C atoms and particularly preferably 1 to 4 C atoms, with the proviso that the sum of the C atoms in R ⁵ and R ^{6 is} not more than 9. R ⁵ and R ^{6 are} each preferably linear alkyl groups. R ⁶ is particularly preferably a methyl group. For example, it may be -CH ₂ -CH (CHs) -OH. In such branched (meth) acrylic acid esters, the tendency of the OH group to form further ester bonds with other COOH-containing monomers is significantly reduced. Very particularly preferred are -CH ₂ -CH (CHs) -OH and / or -CH (CHs) -CH ₂ -OH, in particular a mixture of the two radicals. (Meth) acrylic acid esters with such radicals can in a simple manner, for. B. by esterification of (meth) acrylic acid with 1, 2-propylene glycol.

The radicals R ^2c are mono- or oligosaccharide radicals, preferably monosaccharide radicals. It can in principle be all kinds of saccharides. Preference is given to using radicals derived from pentoses and hexoses, in particular from hexoses. Examples of suitable monosaccharides include glucose, mannose, galactose, fructose or ribose. Preferably, glucose-derived radicals can be used. They may also be derivatives of the saccharides, for example products resulting from the reduction or oxidation of the saccharides. In particular, these may be sugar acids such as, for example, gluconic acid. The amount of the monomers (C) in the copolymer X1 is 0 to 40% by weight, preferably 1 to 30% by weight.

In addition to the monomers (A), (B), (C) and optionally (D) optionally 0 to 30 wt.% Of at least one further, of (A), (B) and (C) different, ethylenically unsaturated monomer (D. ) are used. In addition, no other monomers are used.

The monomers (D) serve to fine-tune the properties of the copolymer X1. Of course, several different monomers (D) can be used. They are selected by the skilled person depending on the desired properties of the copolymer and further with the proviso that they must be copolymerizable with the monomers (A), (B) and (C).

They are preferably monoethylenically unsaturated monomers. In special cases, however, small amounts of monomers having a plurality of polymerizable groups can also be used. As a result, the copolymer can be crosslinked to a small extent.

Examples of suitable monomers (D) include in particular aliphatic alkyl esters of (meth) acrylic acid, such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate or 2-ethylhexyl (meth) acrylate. Also suitable are vinyl or allyl ethers, e.g. Methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, 2-ethylhexyl vinyl ether, vinylcyclohexyl ether, vinyl 4-hydroxybutyl ether, decyl vinyl ether, 2- (diethylamino) ethyl vinyl ether, 2- (di-n-butylamino) ethyl vinyl ether or methyl diglycol vinyl ether or the corresponding allyl compounds. Also used may be vinyl esters such as vinyl acetate or vinyl propionate. It is also possible to use basic comonomers, for example acrylamide and alkyl-substituted acrylamides.

Examples of crosslinking monomers include molecules having a plurality of ethylenically unsaturated groups, for example di (meth) acrylates such as ethylene glycol di (meth) acrylate or butanediol-1,4-di (meth) acrylate or poly (meth) acrylates such as trimethylolpropane tri (meth) acrylate or di (meth) acrylates of oligo- or polyalkylene glycols such as di-, tri- or tetraethylene glycol di (meth) acrylate. Other examples include vinyl (meth) acrylate or butanediol divinyl ether.

The amount of all monomers (D) used together amounts to 0 to 30% by weight, based on the total amount of the monomers used. Preferably, the amount is 0 to 20 wt.%, Particularly preferably 0 to 10%. If crosslinking monomers (D) are present, their amount should as a rule not exceed 5%, preferably 2% by weight, based on the total amount of all monomers used for the process. It may be, for example, 10 ppm to 1 wt.%. In a first preferred embodiment of the invention, the copolymer X1 contains, in addition to (A), at least one monomer (B). In addition to the monomers (A) and (B), other monomers (C) or (D) are preferably present. The amount of (A) in this embodiment is preferably 60 to 90% by weight and the amount of (B) 10 to 40% by weight. Particularly preferred in this embodiment is a copolymer X1 of acrylic acid and maleic acid or acrylic acid and itaconic acid in the abovementioned amounts.

In a second preferred embodiment of the invention, the copolymer X1 contains (A) at least one monomer (B1) and at least one monomer (B2). Further particularly preferred, apart from the monomers (A), (B1) and (B2), no further monomers (D) are present. The amount of (A) in this embodiment is preferably 50 to 90 wt%, the amount of (B1) 5 to 45 wt%, the amount (B2) 5 to 45 wt%, and the amount of (D) 0 up to 20% by weight. Particular preference is given to a copolymer X1 of acrylic acid, maleic acid and vinylphosphonic acid in the abovementioned amounts.

In a third, preferred embodiment of the invention, the copolymer X1 contains (A) at least one monomer (B2) and at least one monomer (C). The amount of (A) in this embodiment is preferably 20 to 60 wt%, the amount (B2) is 20 to 60 wt%, the amount of (C) is 1 to 40 wt%, and the amount of (D) is 0 up to 20% by weight. Particular preference is given to a copolymer X1 of acrylic acid, vinylphosphonic acid and hydroxyethyl acrylate and / or hydroxypropyl acrylate.

The preparation of the polymers X can be carried out by methods known to the person skilled in the art. The copolymers are preferably prepared by free-radical polymerization of the stated components (A), (B) and optionally (C) and / or (D) in aqueous solution. Details for carrying out a radical polymerization are known to the person skilled in the art. Preparation processes for the copolymers X1 are described, for example, in WO 2006/021308 or in WO 2006/1341 16, page 9, line 38 to page 13, line 24.

The synthesized copolymers X1 can be isolated from the aqueous solution by conventional methods known to those skilled in the art, for example by evaporation of the solution, spray drying, freeze drying or precipitation. However, the copolymers X1 are preferably not isolated at all from the aqueous solution after the polymerization, but the solutions of the copolymers obtained are - gf. after addition of further additives, used as such for the process according to the invention. In order to facilitate such direct reuse, the amount of aqueous solvent used for the polymerization should be from the beginning so dimensioned that the concentration of the polymer in the solvent is suitable for the application. It can also be first prepared a concentrate, which only on site with water or optionally diluted with other solvent mixtures to the desired concentration.

The molecular weight M _w (weight average) of the polymers X or copolymers X1 used for the process according to the invention is determined by the person skilled in the art according to the desired application. For example, polymers having a molecular weight M _w of 3000 to 1 000 000 g / mol can be used. Polymers having from 5000 g / mol to 500 000 g / mol, preferably from 10 000 g / mol to 250 000 g / mol, more preferably from 15 000 to 100 000 g / mol and very particularly preferably from 20 000 to 75 000 g, have proven particularly useful / mole.

Formulations with polymers Y

The polymers Y have one or more different basic groups. The basic groups are preferably groups comprising at least aliphatic and / or aromatic amino groups, and more preferably heterocycles having 5-6 ring members and 1-3 nitrogen atoms.

In a preferred embodiment of the invention, the polymer Y may be polyethyleneimine (PEI) or derivatives of polyethylenimine. Derivatives may in particular be N-functionalized derivatives of polyethylenimine, in particular derivatives which have> N- (CH 2) xS groups, where x is preferably 1 or 2 and S is an acidic group, in particular a carboxyl group. pe or a phosphonic acid group. Such PEI derivatives can be obtained, for example, by reacting unfunctionalized PEI with acrylic acid or vinylphosphonic acid.

In a further preferred embodiment of the invention may be polymers Y based on corresponding vinyl compounds. Examples of suitable monomers for the construction of such polymers Y include vinylimidazole, vinyllactams such as N-vinylcaprolactam, N-vinylpyrrolidone or other vinyl heterocycles such as vinylpyridine. They are preferably polymers comprising vinylimidazole. In addition, they may also contain other comonomers, such as, for example, alkyl acrylates or monomers comprising acidic groups. For example, basic polymers Y suitable for passivation are disclosed in WO 2004/081128.

In order to achieve the desired acidic pH, additional acids are generally added to the formulation as described above. If the polymers Y in addition to the basic groups have a sufficient amount of additional acidic groups, it may be possible to dispense with the addition of acids. IR spectroscopic investigations

The selection of the IR bands to be used for spectral analysis and control depends on the formulation (F) used in each case. The person skilled in the art will make a suitable choice depending on the components. The process according to the invention can be used particularly advantageously if the tempering layer contains organic components. In particular, C-H bands can be measured here and the bands of various functional groups, in particular> C = O bands, for example> C = O bands in keto groups, carboxylic acid groups, carboxylate groups, complexed carboxylate groups or carboxylic acid ester groups.

The process according to the invention can very particularly advantageously be used if the surface treatment is a passivation, and the formulation used for passivation comprises water-soluble or water-dispersible polymers. Particularly preferred in this embodiment of the invention by means of the Fourier transform IR spectrometer bands with maxima at 2500-3500 cm- ¹ and / or at 1400-2000 cm- ¹ measured. While at 2500 to 3500 cm ^-1, for example, CH absorptions of the polymer backbone or the polymer side chain can be found, suitable IR absorptions of functional groups, for example C = O absorptions, are frequently found between 1400-2000 cm ^-1 .

The process according to the invention is particularly suitable for passivation with polymers X which comprise -COOH groups. On the one hand, the carboxyl group has a strong, readily analyzable IR band in the range mentioned. Above all, the position of the band is shifted by the chemical environment of the carboxyl group, so that conclusions about the structure of the layer can be obtained from the wavelength at which IR absorptions occur. For example,> C (= O) -OH and> C (= O) -OM, where M is a metal ion (eg Zn ²⁺ ), can be distinguished by IR spectroscopy. When passivated with -COOH-containing polymers, the aqueous formulation reacts after application of the formulation on the galvanized surface and releases Zn ²⁺ ions from the zinc layer. The acidic groups of the polymer anchor the polymer to the surface and the detached Zn ²⁺ ions crosslink the polymer layer. A high-quality passivation layer is therefore characterized by a high proportion of> C (= O) -O-Zn absorptions and a qualitatively poor by a high proportion of> C (= O) -OH. The following examples are intended to illustrate the invention by way of example:

The following formulations were used for passivation:

Formulation I:

Aqueous formulation with 25% by weight of polyacrylic acid (M _w about 40,000 g / mol, 1.39 mol of acid groups / 100 g of the polymer) and 0.5% by weight of nitric acid based on the formulation. The pH of the formulation was 0.9.

Formulation II:

Aqueous formulation with 20% by weight of polyacrylic acid (M _w approx. 40,000 g / mol, 1.39 mol of acid groups / 100 g of the polymer) and 0.5% by weight of nitric acid based on the formulation. The pH of the formulation was 0.9.

Formulation III:

Aqueous formulation containing 25% by weight of polyacrylic acid (M _w approx. 40,000 g / mol, 1.39 mol of acid groups / 100 g of the polymer) and 2.3% by weight of nitric acid based on the formulation. The pH of the formulation was 0.4.

Passivation:

The formulations were each applied to a galvanized steel strip using a belt coater analogously to FIG. The FT-IR spectrometer was mounted at a distance of about 20 m behind the dryer above the steel strip. The metal strip had a width of 950 mm and the belt speed was 120 m / min.

The sprayed amount of formulation was the same. In formulation I, a coating layer with a thickness of about 0.5 .mu.m was obtained in formulation II with a thickness of about 0.2 .mu.m and in formulation III with a thickness of about 0.5 .mu.m.

discussion of the results

The FT-IR spectra of the layers applied with the formulations I, II and III are shown in FIG. 6 (formulation I). The spectra are shown as absorption spectra.

Despite identical chemical components in the formulation, namely in each case only nitric acid and polyacrylic acid, the three FT-IR spectra of the respectively obtained passivation layers differ significantly from one another. In particular, the spectra show a difference in signal strength at 1720 cm ^-1 (C (= O) OH). This difference in signal strength reflects the difference in layer thickness. With the more concentrated formulation I was a layer thickness of about 0.5 microns, with the less concentrated formulation Il a layer thickness of about 0.2 microns.

The thicker layer absorbs more IR radiation and accordingly the intensity of the band is greater at 1720 cm ^-1 (the spectra are shown as absorption spectra).

The spectrum of the passivation layer obtained by means of formulation III shows the use of the method according to the invention for analyzing the composition of the passivation layer. Formulation III, like formulation I, contains 25% by weight of polyacrylic acid, but 2.3% by weight of nitric acid compared with 0.5% by weight in formulation I. The higher nitric acid concentration leads to more Zn ²⁺ ions in the course of the passivation dissolved from the metal surface than when using the formulation I with lower acid content. Zn ²⁺ ions are complexed by the carboxyl groups of the polymer and thus crosslink the passivation layer. As a result, a better quality layer is obtained. The corresponding FT-IR spectrum shows not only the band at 1,720 cm ^-1 but also a very intense band at 1570 cm ^-1 . This band can be assigned to the (C (= O) OZn) group. The crosslinking density of the passivation layer can therefore be determined directly via the intensity measurement of the band at 1570 cm ^-1 .

Claims

claims

A process for the continuous surface treatment of a metal strip with a liquid formulation (F), in which a metal strip is moved in the longitudinal direction through a device for the surface treatment of metal strips, which at least

• a device (3) for applying the formulation (F) and

Comprising a drying station (5),

wherein the formulation (F) comprises at least one solvent and coating-forming components, the formulation (F) is applied to the metal strip by means of the device (3), the solvents are at least partially removed by means of the drying station, the amount of the formulation to be applied being determined measures that forms a non-metallic coating layer with a dry film thickness of less than 3 microns on the metal surface, characterized in that the device used - viewed in the direction of the belt - after the drying station (5) with at least one, a coated side of the tape facing, working in reflection geometry Fourier-transform IR spectrometer (6) is equipped with the IR-spectroscopic measured data for characterizing the surface are recorded by the applied coating layer while the metal strip is running.

2. The method according to claim 1, characterized in that the metal strip is mounted on the side remote from the Fourier transform IR spectrometer side of the metal strip with a support or guide roller (8), which not more than 4 m from the point IR measurement is removed.

3. The method according to claim 1 or 2, characterized in that the distance of the Fourier transform IR spectrometer is variable to the strip surface.

4. The method according to any one of claims 1 to 3, characterized in that the measured data obtained are converted in a computing unit into a quality value.

5. The method according to claim 4, characterized in that the quality value increases or decreases with the layer thickness of the coating layer.

6. The method according to claim 4 or 5, characterized in that the amount of the formulation to be applied (F) is controlled depending on the quality value.

7. The method according to claim 4 or 5, characterized in that the composition of the formulation to be applied (F) is controlled depending on the quality value.

8. The method according to any one of claims 1 to 7, characterized in that Fourier transform IR spectrometer (5) in the range of 200 to 4000 cm " ¹ operates.

9. The method according to claim one of claims 1 to 8, marked thereby, that it is the metal strip to a steel strip or a galvanized

Steel band acts.

10. The method according to claim 9, characterized in that it is a passivation in the surface treatment.

1 1. A method according to claim 10, characterized in that it is a Phosphatpassivierung, in which an acidic, aqueous formulation having a pH <5 is used, which in addition to water comprises at least phosphoric acid and / or phosphate and at least one metal ion ,

12. The method according to claim 9, characterized in that one uses an acidic, aqueous formulation with a pH <5, which comprises, in addition to water, at least one water-soluble or water-dispersible polymer for passivation.

13. Process according to claim 12, characterized in that the polymer is at least one water-soluble polymer X comprising acidic groups.

14. The method according to claim 13, characterized in that it is the acidic groups -COOH groups and / or salts thereof.

15. The method according to claim 12, characterized in that it is the polymer is a water-soluble, basic groups comprising polymer Y.

16. Process according to claim 15, characterized in that the basic groups are groups which are at least aliphatic and / or aromatic amino groups.

17. Process according to claim 15, characterized in that the basic group is a heterocycle having 5-6 ring members and 1-3 nitrogen atoms.

18. The method according to any one of claims 12 to 17, wherein by means of the Fourier transform IR spectrometer (5) bands with maxima at 2500-3500 cm " ¹ and / or at 1400-2000 cm" ^{1 is} missing.

19. The method according to claim 18, characterized in that one misses> C = O - bands.

20. The method according to claim 18, characterized in that one misses C-H - bands.