WO2003042426A2

WO2003042426A2 - Regulation of the accelerator concentration in phosphating baths

Info

Publication number: WO2003042426A2
Application number: PCT/EP2002/012304
Authority: WO
Inventors: Patrick Droniou
Original assignee: Henkel Kommanditgesellschaft Auf Aktien; Nihon Parkerizing Co., Ltd.
Priority date: 2001-11-14
Filing date: 2002-11-05
Publication date: 2003-05-22
Also published as: DE10155976A1; AU2002357999A1; WO2003042426A3

Abstract

The invention relates to a method for phosphating metallic surfaces. According to the inventive method, a) a correlation between the result of the phosphation, the accelerator content and at least one other characteristic parameter for the phosphation process is determined or pre-defined, b) the accelerator content is determined, c) the at least one other characteristic parameter for the phosphation process is detected or determined, d) a nominal value for the accelerator content is calculated on the basis of the correlation which is determined or pre-defined in step a) and on the basis of the at least one other characteristic parameter for the phosphation process, said nominal value leading to a desired, previously fixed phosphation result, and e) in the event of the nominal value for the accelerator content, calculated in step d), being higher than the value determined in step b), a quantity of accelerator is added to the phosphating bath, by activation of a dosing device, such that the nominal value of the accelerator calculated in step d) is reached.

Description

"Control of the Accelerator Concentration in Phosphating Baths"

The invention relates to a method for controlling the accelerator concentration in the phosphating of metal surfaces with aqueous, acidic phosphating solutions which contain zinc and phosphate ions and at least one accelerator.

The phosphating of metals pursues the goal of producing firmly adherent metal phosphate layers on the metal surface, which in themselves improve corrosion resistance and, in conjunction with paints and other organic coatings, contribute to a significant increase in adhesion and resistance to infiltration when exposed to corrosion. Such phosphating processes have long been known in the prior art. For the pretreatment before painting, the low-zinc phosphating processes are particularly suitable, in which the phosphating solutions have comparatively low contents of zinc ions of e.g. B. 0.5 to 2 g / l.

It has been shown that by using other polyvalent cations than zinc in the phosphating baths, phosphate layers with significantly improved corrosion protection and paint adhesion properties can be formed. For example, find low-zinc processes with the addition of z. B. 0.5 to 1.5 g / l of manganese ions and z. B. 0.3 to 2.0 g / l of nickel ions as a so-called trication method for the preparation of metal surfaces for painting, for example for the cathodic electrocoating of car bodies, wide application.

DE-A-40 13 483 discloses phosphating processes with which similarly good corrosion protection properties can be achieved as with the trication processes. These processes do without nickel and instead use copper in low concentrations, 0.001 to 0.03 g / l.

Oxygen and / or other oxidizing agents with the same effect are used to oxidize the divalent iron formed in the pickling reaction of steel surfaces to the trivalent stage. As such, nitrite, chlorate, bromate, peroxy compounds as well organic nitro compounds, such as nitrobenzenesulfonate. German patent application DE 42 10513 modifies this process by adding hydroxylamine, its salts or complexes in an amount of 0.5 to 5 g / l hydroxylamine as a modifying agent for the morphology of the phosphate crystals formed.

EP-B-414 296 discloses a method for phosphating iron and steel surfaces according to the low zinc technology with a phosphating solution, to which hydrogen peroxide or alkali perborate is added in such an amount that the maximum peroxide concentration is 17 mg / l. The addition of hydrogen peroxide and / or alkali perborate can be controlled in accordance with the electrochemical potential determined with a redox electrode.

The unpublished German patent application DE-A-101 18 552 relates to a method for phosphating metal surfaces made of steel, galvanized or galvanized steel, aluminum and / or aluminum alloys, in which the metal surfaces are sprayed or dipped for a period between 3 Seconds and 8 minutes in contact with a zinc-containing phosphating solution containing 0.2 to 3 g / l zinc ions and 3 to 50 g / l phosphate ions, the weight ratio of phosphate ions to zinc ions being at least 3.7, and one or more accelerators selected

0.3 to 4 g / l chlorate ions,

0.01 to 0.2 g / l nitrite ions,

0.05 to 2 g / l m-nitrobenzenesulfonate ions,

0.05 to 2 g / l m-nitrobenzoate ions,

0.05 to 2 g / l p-nitrophenol,

0.005 to 0.15 g / l hydrogen peroxide in free or bound form,

0.1 to 10 g / l hydroxylamine in free or bound form,

0.1 to 10 g / l of a reducing sugar

0.05 to 4 g / l of an organic N-oxide, preferably N-methymorpholine,

Contains 0.5 to 5 g / l of an organic nitro compound selected from nitroguanidine, nitroarginine and methyl, ethyl or propyl esters thereof and from nitrofurfurylidene diacetate, the concentration of the accelerator being determined using a biochemical hydrogen peroxide sensor which provides an electrical signal whose height the concentration of the accelerator can be derived. Methods for phosphating metal surfaces with phosphating baths according to the above composition are known in the prior art. The task always is to determine the accelerator content, which decreases without any control measures during the phosphating process, and to keep it in the vicinity of a specified setpoint.

EP-A-196 259 describes a method for adapting the composition of a chemical treatment solution for the treatment of a substrate so that optimal treatment results are achieved. To do this, a correlation is established between the composition of the treatment solution and the treatment results. This can be done, for example, in the form of a mathematical series development. To do this, you systematically change the composition of the process solution and record how this change affects the treatment result. The coefficients of the series development can be derived from these experiments. In this way it can be seen which parameter change affects the treatment result and in what way. With the help of this knowledge, the composition of the treatment solution, for example a phosphating solution, can be adjusted so that a desired treatment result is achieved.

An alternative approach to optimizing and controlling the composition of a chemical treatment solution is described in WO 00/36183. According to the method proposed there, one or more parameters which characterize a chemical or physical treatment of a substrate are recorded continuously or at regular intervals and at the same time the result of the treatment of the substrate is recorded. This can be done manually, semi-automatically or even fully automatically. The result is again a correlation between the treatment parameters and the treatment result, and from the learned connection, if the result deviates from a desired target value, the parameters which are responsible for the deviation can be corrected. In this way, an expert system can be obtained which can automatically detect deviations of a treatment result from predetermined target values and take the necessary corrective measures.

The object of the present invention is to adjust the accelerator content of a phosphating solution in such a way that the desired phosphating result is obtained even if there is another parameter or in addition to the accelerator content change several other parameters that also affect the phosphating result. In contrast to the previous state of the art, a setpoint for the accelerator content that is to be specified should not be set, but rather the setpoint should be adapted to changing conditions during the process.

The present invention relates to a method for phosphating metal surfaces made of one or more materials selected from steel, galvanized or alloy galvanized steel, aluminized or alloy aluminized steel or from aluminum or magnesium or in each case their alloys which consist of at least 50 atomic percent of aluminum or magnesium , wherein to deposit a phosphate layer, the metal surfaces are brought into contact with an acidic aqueous phosphating solution which contains 0.3 to 10 g / l of zinc ions, 5 to 100 g / l of phosphate ions, calculated as PO ₄ ^{3 "} , and one or more accelerators , characterized in that a) a correlation between the result of the phosphating, the content of the accelerator or, in the presence of several accelerators, a selected accelerator and at least one other parameter characteristic of the phosphating process is determined or specified, b) manually or program-controlled determines the content of (selected) accelerator, c) manually or program-controlled detects or determines the at least one further parameter characteristic of the phosphating process, d) from the correlation determined or specified in sub-step a) and on the basis of the at least one recorded or determined in sub-step c) a further parameter characteristic of the phosphating process calculates a target value for the content of the (selected) accelerator, which leads to a previously specified desired phosphating result, and e) in the event that the target value for the (selected) content calculated in sub-step d) Accelerator is greater than the value determined in sub-step b) by activating a metering device to add such an amount of (selected) accelerator to the phosphating bath that the setpoint of the (selected) accelerator calculated in sub-step d) is set.

The phosphating solution preferably has the following further parameters which are characteristic of the phosphating process: a pH in the range from 2.5 to 3.8, one Free acid content in the range of 0 to 2.5 points and total acid content in the range of 15 to 30 points.

The concentration data for Zn and phosphate span the range of low zinc phosphating, which is usually carried out as the basis for subsequent painting, as well as the range of normal or high zinc phosphating, which is usually used to create a sliding layer for cold forming. For the low zinc phosphating, the zinc contents are preferably selected in the range from 0.3 to 3 g / l, in particular up to 2.5 g / l, and the phosphate contents in the range from 3 to 30 g / l. It is further preferred that the mass ratio between zinc ions and phosphate ions is in the range from 1:10 to 1:20. In normal or high zinc phosphating, zinc contents in the range from 3 to 10 g / l and phosphate contents above 20 g / l, in particular above 30 g / l, are preferably chosen.

The sub-steps b) to e) are carried out again and again during the course of the method according to the criteria explained below. On the other hand, it is sufficient to carry out process step a) once at the start of the process. If the required correlation is already known, it is sufficient to specify it at the start of the procedure. "Pretend" means that, for example, the known correlation is recorded in a documentation which will be used in the further course of the method. This documentation can be aimed at a person who carries out the method according to the invention. However, it is preferable that the method according to the invention is possible The known correlation is stored in an EDP system so that the control computer can use it to carry out the method If the required correlation is not already known at the beginning of the method, it must first be carried out by laboratory experiments or on a technical scale The method described in WO 00/36183 is suitable, for example, for the determination on an industrial scale.

The correlation can be determined and represented in laboratory tests or on an industrial scale in a manner as is apparent from EP-A-196 259. In the simplest case, such a correlation can be expressed by equation (1),

in which Y represents a result of the phosphating, for example the area-related mass of the phosphate layer, the proportion of a selected component in the phosphate layer or one of the quantities listed below. Xi is the accelerator concentration, X ₂ the value of another parameter which, together with the accelerator concentration, influences the phosphating result Y. b ₀ , bi and b ₂ are the coefficients of the series expansion, which determine how Xi and X influence the result Y. A number of experiments are now carried out in which X! and X _{2 are} systematically varied, and each determines the phosphating result Y. The numerical values of the coefficients b ₀ , bi and b ₂ can be determined from this by means of mathematical compensation methods, preferably using the least squares method. If not only another parameter X _{2 is} to be taken into account in addition to the accelerator concentration Xi, but also further parameters X _n , the series must be supplemented accordingly.

The accuracy of the correlation can be increased by including mixed terms in the series development. Equation (1) is then expanded to equation (2).

Y = b ₀ + bΛ + b ₂ X ₂ + b ₁₂ X | X ₂ (2)

If further parameters X _{n are taken} into account, the series development must be supplemented accordingly. A series completed in this way can be written down in the manner of equation (3)

Y = b _o + biXi + b ₂ X ₂ ... + b | _< Xk + ... + b _n X _n + bι ₂ XιX ₂ + ■ • ■ + b -ii k-iXk ⁺ ■ •• ⁺ bkkXk ⁺ ■ • ■ ⁺ + b _nn X _n ² (3)

For further details, reference is made to EP-A-196 259. In the context of the present invention, the method described in this document can therefore be used to carry out sub-step a). However, this document does not disclose to use the correlation obtained to carry out sub-steps b) to e) according to the invention repeatedly.

The accelerator or accelerators can be selected from the substances known for this purpose in the prior art. For example, the phosphating solution can contain one or more of the following accelerators, as is known from document DE-A-101 18 552 cited above: 0.3 to 4 g / l chlorate ions, .01 to 0.2 g / l nitrite ions,

0.05 to 2 g / l m-nitrobenzenesulfonate ions,

0.05 to 2 g / l m-nitrobenzoate ions,

0.05 to 2 g / l p-nitrophenol,

0.005 to 0.15 g / l hydrogen peroxide in free or bound form,

0.1 to 10 g / l hydroxylamine in free or bound form,

0.1 to 10 g / l of a reducing sugar

0.05 to 4 g / l of an organic N-oxide, preferably N-methymorpholine,

0.5 to 5 g / l of an organic nitro compound selected from nitroguanidine, nitroarginine and methyl, ethyl or propyl esters thereof and from nitrofurfurylidene diacetate.

In the course of the phosphating process, hydrogen ions in the phosphating solution are reduced to hydrogen atoms on the metal surface, metal atoms on the metal surface being oxidized and either being incorporated into the phosphate layer or being released into the phosphating solution as ions. The hydrogen produced polarizes the metal surface in such a way that the further chemical reaction of the phosphating solution with the metal surface is hindered. If the hydrogen atoms are not consumed by a chemical reaction shortly after their formation, hydrogen bubbles are formed on the metal surface, which additionally hinder the phosphating process. Substances which can react with the atomic hydrogen on the metal surface or which are reduced in the reaction of the phosphating solution with the metal surface instead of the hydrogen ions are referred to as "accelerators". Examples are contained in the above list.

If the accelerators are sufficiently strong oxidizing agents, they can oxidize divalent iron ions that arise during the phosphating of steel surfaces to the trivalent stage. These precipitate out of the phosphating solution as iron (III) phosphate and are removed from the phosphating solution as phosphating sludge. Fe (ll) ions also dissolve in the phosphating of galvanized steel, since the iron-containing base material is exposed at the cut edges. Accordingly, the accelerators can be divided into those which prevent the formation of elemental hydrogen on the metal surface, but cannot oxidize divalent iron ions to trivalent ones, and those which also have the second ability. An example of the first group is hydroxylamine. This can be done as such, in the form of salts or as Compound are introduced into the phosphating solution, which cleaves off hydroxylamine under the conditions of the phosphating solution. Examples of such compounds are acetaldehyde oxime and acetoxime (WO 96/16204). The second group of accelerators includes strong oxidizing agents such as hydrogen peroxide and compounds that form hydrogen peroxide in the phosphating solution. Examples of peroxide-forming substances are ionic compounds such as, for example, alkali metal peroxides or molecules or ions which carry a peroxo group which forms hydrogen peroxide in the phosphating bath. Examples are perborates, inorganic peracids and their salts such as, for example, peroxosulfuric acid or peroxodisulfuric acid, and organic peracids and their salts.

Depending on the chemical properties of the accelerator, different methods are known for determining the concentration of the accelerator manually or automatically. The redox properties of the accelerator are often used for this. For example, nitrite is reduced to elemental nitrogen, the volume of which is measured. Oxidizing accelerators such as hydrogen peroxide or substances with peroxo groups can be determined manganometrically. Furthermore, the determination with redox-active electrodes or with special hydrogen peroxide sensors is known. The latter measurement method is described in DE-A-101 18 552. It also describes that this sensor technology can also be used to indirectly determine other accelerators if they react with hydrogen peroxide. An example of this is hydroxylamine. Another method for determining hydroxylamine is titration with sodium hydroxide solution in the presence of acetone. Here, hydroxylamine forms an oxime with acetone and the acid released is detected by the acid-base titration. Furthermore, hydroxylamine and substances which can split off hydroxylamine can be determined by redox reaction with cerium ammonium sulfate and iron sulfate.

Several accelerators can also be used at the same time. For example, nitrate ions can additionally be present as co-accelerators. Hydrogen peroxide as an accelerator can be combined with chlorate ions, for example. Or, for example, hydroxylamine is used together with nitrobenzenesulfonate ions. In such cases, one selects a “main accelerator” that has the greatest influence on the phosphating result, and uses this as the “selected” accelerator to carry out the process according to the invention. If, therefore, above and in claim 1, there is talk of a “(selected) accelerator”, this means either the only accelerator in the phosphating solution or the main accelerator to be selected. If the phosphating solution contains several accelerators, the "selected accelerator" is preferably the one that is consumed the fastest or decomposes fastest.

In the process sequence according to the invention, it is in principle irrelevant in what order the sub-steps b) and c) are carried out. It is only important that the sub-steps b) and c) are carried out in a close time context, for example within half an hour. The sub-steps b) and c) can also be carried out simultaneously. It is only necessary that the results of sub-steps b) and c) are available at the beginning of sub-step d). In step c), the at least one further parameter characteristic of the phosphating process can be determined by a chemical or physical measurement. However, the further parameter can also be acquired manually or automatically in another way and entered into the control system. For example, the further parameter can be the material of the metal surface that is to be phosphated. This information can, for example, be recorded by the operating personnel of the system in which the method according to the invention is carried out and used for sub-step d) or entered into the control system for the method according to the invention.

For sub-step d) it must be specified what is desired as a result of the phosphating. Of course, this specification can be changed in the further course of the process sequence b) to e).

Since the accelerator is consumed in the course of the phosphating, it can be expected that the target value for the accelerator calculated in sub-step d) will be greater than the value determined in sub-step b). If this is the case, a dosing device is activated manually or automatically in sub-step e), which adds such an amount of (selected) accelerator to the phosphating bath that the target value calculated in sub-step d) is reached within a tolerance value of the type depends on the dosing device. Together with the (optionally selected) accelerator, further components can be added to the phosphating bath, for example one or more co-accelerators.

If the setpoint for the content of (selected) accelerator calculated in sub-step d) is exceptionally smaller than that determined in sub-step b), it could one deliberately reduces the accelerator content by chemical reaction. To do this, one would have to add a calculated amount of a substance to the phosphating solution, which degrades the accelerator through a chemical reaction. In practice, however, it should be sufficient to continue phosphating without changing the accelerator content until the accelerator content reaches or falls below the setpoint due to consumption and dragging out.

Sub-step c) provides that manually or program-controlled, at least one further parameter (that is, apart from the accelerator or the selected accelerator) is recorded or determined for the phosphating process. These parameters include, for example, the physical and chemical properties of the phosphating solution and the type of application. For example, the phosphating solution can have a temperature in the range from 30 to 65 ° C. The metal surface can be brought into contact with the phosphating solution for a period of time in the range from 30 to 300 seconds. The temperature of the phosphating solution and the contact time with the metal surface are characteristic parameters for the phosphating process.

Furthermore, the parameters characteristic of the phosphating process include

Concentrations of other optional components of the phosphating solution. For example, the phosphating solution can additionally be selected from one or more constituents

2 to 200 mg / l copper ions,

0.05 to 3 g / l manganese ions,

0.02 to 3 g / l nickel ions,

0.02 to 1 g / l free fluoride ions,

0.1 to 2 g / l fluorocomplex anions of the elements boron, silicon, titanium and / or zircon,

0.001 to 3 g / l of organic polymers which contain nitrogen and / or oxygen atoms,

Contain 0.1 to 10 g / l nitrate ions. These components are known as components of phosphating solutions in the prior art.

The parameters characteristic of the phosphating process also include the way in which the metal surface is brought into contact with the phosphating solution. For example, the metal surface can be immersed in the phosphating solution (immersion method) or washed over with the phosphating solution (flooding method). Practice shows that the phosphating result depends on the speed with which the phosphating solution moves relative to the metal surface. In the case of immersion or flood processes, this speed is in the range from approximately 0.1 to approximately 20 m / sec. In flooding processes, the speed can be influenced by the amount of phosphating solution that is rinsed over the metal surface per unit of time. In immersion processes, the speed of the phosphating solution relative to the metal surface is generally adjusted by pumping the phosphating solution around or by stirring. A further, albeit smaller, contribution is made by the movement of the metal surface relative to the container in which the phosphating solution is located, which is caused by the transport device for the metal surface.

As an alternative to or in addition to immersion or flooding processes, it is customary in the art to spray the phosphating solution onto the metal surface through nozzles (spraying process). In this case, the pressure at which the phosphating solution is pumped through the nozzles is a parameter which affects the phosphating result. In the case of a spraying process, the phosphating solution is sprayed onto the metal surface at a pressure in the range from approximately 0.4 to approximately 1.2 bar.

The physical and chemical conditions of the phosphating process listed above represent examples of further parameters which are characteristic of the phosphating process and which are recorded or determined in accordance with sub-step c). Another parameter characteristic of the phosphating process is the chemical nature of the metal surface or the simultaneous occurrence of different metal surfaces with different chemical properties. For example, the phosphating result will depend on whether the metal surface is steel, electrolytically or hot-dip galvanized or alloy-galvanized steel, aluminized or alloy-aluminized steel or aluminum or magnesium or their alloys. In the case of alloys, the chemical composition plays a role. Even with unalloyed steel, the phosphating result can depend on the exact chemical composition of the steel surface, which contains carbon atoms in addition to iron atoms. In the context of the method according to the invention, a correlation between the result of the phosphating, the content of the (selected) accelerator and the chemical nature of the metal surface or the material mixture of the metal surfaces is determined in sub-step a). If this correlation is already known, it can be used directly for the further process steps. In step c), the information about the chemical is added to the control system for the method according to the invention Nature of the metal surface or the material mix, so that the relationship between accelerator content, phosphating result and chemical nature of the metal surface known in partial step a) can be used in partial step d) in order to determine a target value for the accelerator content. This entry into the control system can be made manually if the chemical nature of the metal surface or the material mixture is changed in the course of the method. However, the chemical nature of the metal surface can also be determined automatically by a suitable measuring method, for example with the aid of an X-ray fluorescence measurement. However, information about the chemical nature of the metal surface can also be given to the parts to be phosphated in machine-readable form, for example by means of a bar code or some other optical or magnetic information carrier. In step c) this information is read automatically.

In the sense of the method according to the invention, a further parameter characteristic of the phosphating is the expected value for the total size of the metal surface which comes into contact with the phosphating solution between the sub-step b) which has just taken place and the next (e.g. time-controlled) execution of the sub-step b) will be brought. In the case of a phosphating plant operated at constant capacity, this parameter is essentially constant, so that it usually does not play a role in the course of the method according to the invention. However, this changes when a process is interrupted, for example when the system is down. In the event of an actual or planned plant shutdown, the control system for the method according to the invention is informed that no or a very small metal surface will be brought into contact with the phosphating solution between two sub-steps b). In this case, the setpoint for the accelerator can be reduced or set to zero. Then no accelerator is metered into the phosphating bath until the control system is informed that the metal surface will again be brought into contact with the phosphating solution. The setpoint for the accelerator is then automatically increased again, so that, depending on the current accelerator content, accelerator is topped up if necessary. This mode of operation of a phosphating bath is more economical than the procedure currently generally carried out, in which the accelerator is kept at a predetermined value, regardless of whether or not the metal surface will be brought into contact with the phosphating solution for a short time. In the prior art, therefore, a phosphating bath is usually always kept ready for operation. Since many accelerators, especially hydrogen peroxide and its derivatives, are also without contact with one decomposing phosphating metal surface, a costly replenishment takes place, although in the short term there is no metal surface to be phosphated. The method according to the invention differs from this in that the target value for the accelerator content is reduced if no metal surfaces to be phosphated are expected, and is increased again if the metal surface to be phosphated is expected. The control system for the method according to the invention can then automatically decide in sub-steps d) and e) whether accelerators should be added or not. This saves the cost of unnecessary metering of accelerators, but the phosphating bath is automatically put back into operational condition if this becomes necessary.

Some other parameters characteristic of phosphating, from which one can

Sub-step d) can calculate the target value for the content of accelerator have already been listed above. These statements can be summarized and supplemented by the fact that the at least one further characteristic of the phosphating

The parameter is selected from: the material or the material mixture of the metal surface, the expected value for the total size of the metal surface which will be brought into contact with the phosphating solution between the sub-step b) which has just taken place and the next intended execution of the sub-step b), the pH Value of the phosphating solution, the temperature of the phosphating solution, the speed with which the phosphating solution reacts during a dipping or

Flooding process moves relative to the metal surface, the pressure with which the phosphating solution is sprayed onto the

Metal surface is sprayed, the length of time for which the phosphating solution is in contact with the metal surface, the free acid content of the phosphating solution, the total acid content of the phosphating solution, the phosphate ion content of the phosphating solution, the zinc ion content of the phosphating solution, the content of the Phosphating solution on one or more of the additional

Components according to claim 4, the content of the phosphating solution in one or more accelerators other than the accelerator determined in sub-step b). In the course of the method according to the invention, sub-steps b) to e) are started and carried out in a regular or irregular sequence or on the basis of special events. In the simplest case, the sequence of sub-steps b) to e) is started by a manual request and then runs automatically under program control. The request for the start of these substeps can be made locally, that is to say at the location of the phosphating system, or from a remote location. In this way it is possible for operating or control personnel who are either at the location of the phosphating system or at a remote location to control the phosphating process by adjusting the accelerator content.

For routine operation, provision is preferably made for the sub-steps b) to e) to be started automatically after a predetermined period of time has elapsed after the process sequence last carried out. A predetermined period of time, which can be, for example, in the range between 1 minute and 8 hours, can be entered into the control system for the method according to the invention. The sub-steps b) to e) then run automatically after the specified time interval. However, a variable time period between two process sequences b) to e) can also be provided, which can depend on the extent of the change in the parameters used. For example, it can be provided that the sequence of the sub-steps b) to e) is restarted after a fixed period of time, for example after an hour, if the setpoint for the accelerator changes within a fluctuation range to be specified. If a major change in the target value is determined, provision can be made to shorten the time span until the next start of the method sequence b) to e). If the change in the setpoints between two determinations decreases again, the time interval can be extended again.

In a further embodiment of the method according to the invention, one can determine manually or automatically at least one result of the phosphating and, in the event of a deviation from a previously specified desired phosphating result (within a tolerance range to be specified), manually or automatically starts the sub-steps b) to e). The control personnel of the system can therefore decide, depending on the phosphating result determined, to start the process sequence b) to e) by means of a manual request. As an alternative to this, a result of the phosphating can be determined automatically as part of an automatic control and monitoring of the phosphating process, the sub-steps b) to e) automatically when the phosphating result deviates from a previously determined desired result be started. The result of this is that if the phosphating result deviates from a previously defined target value, the target value for the accelerator is automatically checked and the accelerator content is adjusted if necessary. In this way, deviations can be corrected without human intervention and production security can be increased.

As a result of the phosphating, which can be used for the correlation in sub-step a), one or more of the following features can be selected: the color of the metal surface after contact with the phosphating solution, the uniformity of the phosphate layer, the layer weight of the phosphate layer, the chemical composition the phosphate layer, the average crystal size or the crystal size distribution in the phosphate layer, the shape of the crystals in the phosphate layer, the electrical impedance of the phosphate layer, the current curve in the case of a cathodic polarization measurement on the phosphate layer, the thickness of a layer deposited on the phosphated metal surface under predetermined deposition conditions cathodic electrodeposition lacquer, the behavior of the phosphate layer coated with a lacquer during a lacquer adhesion and / or corrosion protection test, the electrical loss potential of the substrate in the phosphating solution.

Some of these features require human judgment, and some can also be determined automatically. For example, the color of the metal surface can be determined photometrically. The uniformity of the phosphate layer can be determined, for example, by means of an image analysis, which is described in more detail in WO 00/22574. The. Layer weight of the phosphate layer is determined in the laboratory by detaching the layer and differential weighing. However, methods are known in the prior art for determining the layer weight without damage using infrared measurement (EP 466 226). The chemical composition of the phosphate layer, in particular the content of phosphate or phosphorus and of the layer-forming cations, can be determined non-destructively by means of an X-ray fluorescence measurement. The average crystal size or the crystal size distribution in the phosphate layer or the shape of the crystals in the phosphate layer can be determined by scanning electron micrographs. Measurements of the electrical impedance or recording of the current curve with a cathodic polarization are considered electrochemical Rapid measurements for the corrosion protection effect are known (for example DE-A-195 00 562). Suitable measuring heads are available for measuring the thickness of a deposited layer of a cathodic electrocoat. Paint adhesion and corrosion protection tests are routinely carried out by the phosphating specialist. DIN standards and company-specific standards of individual automobile manufacturers are available for this.

In a special embodiment of the method according to the invention, the turbidity or the sludge content of the phosphating solution is additionally determined. This can be done, for example, by an optical turbidity measurement. In principle, sludge formation in the phosphating bath is undesirable. However, it cannot be prevented in practice, since local supersaturations, which lead to sludge formation, occur, inter alia, when addition solutions are added to the phosphating bath. In order to avoid such local supersaturation as much as possible in a phosphating bath that tends to form sludge, the (selected) accelerator is preferably added to the phosphating bath in sub-step e) in the process according to the invention, the slower the cloudiness or sludge content of the phosphating bath is. As a result, the further sludge formation due to the metering in of the accelerator is kept as low as possible.

Example:

Sheets of automotive cold rolled steel (CRS) were treated according to the following procedure:

1 alkaline degreasing (Ridoline® 1559, Henkel KGaA), 2% in water, 60 ° C, 5 minutes (immersion)

2 rinses with water, room temperature, 1 minute, immersion

3 Activation with an activation suspension containing titanium phosphate (Fixodine® C 9112, Henkel KGaA), 1 g / l, room temperature, 1 minute, immersion

4 Phosphating with a commercially available phosphating solution (Granodine® 952, Henkel KGaA) of the following composition, 2 minutes, spraying at 0.4 bar Composition Granodine® 952:

Zn: 1.1 g / l

Ni: 0.8 g / l

Mn: 0.6 g / l

Free acidity: 0.6 points

Total acidity: 18 points

Accelerator: H2O2 varies between 25 and 100 ppm

Temperature: varies between 51 and 56 ^C C.

The free acid is determined by diluting a 10 ml bath sample with water to 50 ml and titrating with 0.1 N sodium hydroxide solution to a pH of 3.8. The consumption in ml of sodium hydroxide solution gives the free acid score. The total acid is determined accordingly by titrating the bath sample to a pH of 8.5.

Evaluation:

The phosphated, rinsed and dried sheets were assessed optically according to the color of the coating. A yellow color indicates a passivation of the surface with insufficient phosphating. Good phosphating is shown in the greyish color of the sheets. The table below shows the minimum amount of H2O2 required at the selected temperature so that a gray color occurs instead of a yellow color.

This results in the equation for determining the minimum content C ₀ of H2O2 to achieve gray coloring:

C ₀ = 180 / (T-49) with 51 = <T = <56

where C ₀ in ppm H2O2 and

T are expressed in ° C.

With this relationship, the minimum concentration = setpoint for H2O2 can be calculated depending on the temperature, which leads to a gray color. A program sequence for temperature-dependent control of the H2O2 concentration in the phosphating bath described above can be designed, for example, as follows. The temperature can be measured with a thermocouple, the current H2O2 concentration with a measuring electrode.

10 Find current H2O2 concentration C

20 determine current temperature

30 if current temperature between 51 and 56 ° C, go to 40, otherwise go to 80 40 Calculate setpoint C ₀ for H2O2 at the current temperature according to the equation (C ₀ = 180 / (T-49)) 50 if C <C ₀ , add H2O2 to the phosphating bath (dosing amount yes

Preset bath volume, e.g. 5 mg per liter bath solution), otherwise go to 60 wait 5 minutes go after 10 if current temperature is higher than 56 ° C, set C ₀ = 25.7 (as for one

Temperature of 56 ° C), otherwise go to 100

go after 50 set C ₀ = 90 (like for a temperature of 51 ° C) go after 50

Claims

claims

1. A method for phosphating metal surfaces from one or more materials selected from steel, galvanized or alloy galvanized steel, aluminized or alloy aluminized steel or from aluminum or magnesium or their alloys, which consist of at least 50 atomic% of aluminum or magnesium, wherein to deposit a phosphate layer, the metal surfaces are brought into contact with an acidic aqueous phosphating solution which contains 0.3 to 10 g / l of zinc ions, 5 to 100 g / l of phosphate ions, calculated as PO ₄ ^{3 "} , and one or more accelerators characterized in that a) a correlation between the result of the phosphating, the content of the accelerator or, in the presence of several accelerators, a selected accelerator, and at least one further parameter characteristic of the phosphating process is determined or specified, b) the content is set manually or by program control (selected) dam leuniger determines, c) manually or program-controlled detects or determines the at least one further parameter characteristic of the phosphating process, d) from the correlation determined or specified in sub-step a) and on the basis of the at least one further characteristic characteristic of the phosphating process in sub-step c) Parameter calculates a target value for the content of the (selected) accelerator, which leads to a previously specified desired phosphating result, and e) in the event that the target value for the content of (selected) accelerator calculated in sub-step d) is greater than that in Sub-step b) certain value by activating a metering device adds such an amount of (selected) accelerator to the phosphating bath that the setpoint of the (selected) accelerator calculated in sub-step d) is set.

2. The method according to claim 1, characterized in that the phosphating solution selected from one or more accelerators

0.3 to 4 g / l chlorate ions, 0.01 to 0.2 g / l nitrite ions, 0.05 to 2 g / l m-nitrobenzenesulfonate ions, 0.05 to 2 g / l m-nitrobenzoate ions,

0.05 to 2 g / l p-nitrophenol,

0.005 to 0.15 g / l hydrogen peroxide in free or bound form,

0.1 to 10 g / l hydroxylamine in free or bound form,

0.1 to 10 g / l of a reducing sugar

0.05 to 4 g / l of an organic N-oxide, preferably N-methymorpholine,

Contains 0.5 to 5 g / l of an organic nitro compound selected from nitroguanidine, nitroarginine and methyl, ethyl or propyl esters thereof and from nitrofurfurylidene diacetate.

3. The method according to one or both of claims 1 and 2, characterized in that the phosphating solution has a temperature in the range from 30 to 65 ° C and that the metal surface is brought into contact with the phosphating solution for a period in the range from 30 to 300 seconds becomes.

4. The method according to one or more of claims 1 to 3, characterized in that the phosphating additionally selected one or more components

2 to 200 mg / l copper ions,

0.05 to 3 g / l manganese ions,

0.02 to 3 g / l nickel ions,

0.02 to 1 g / l free fluoride ions,

Contains 0.1 to 10 g / l nitrate ions.

5. The method according to one or more of claims 1 to 4, characterized in that the phosphating solution moves in a dipping or flooding process at a speed in the range of 0.1 to 20 meters per second relative to the metal surface.

6. The method according to one or more of claims 1 to 4, characterized in that the phosphating solution in the case of a spraying process with a pressure in the range from 0.4 to 1.2 bar is sprayed onto the metal surface.

7. The method according to one or more of claims 1 to 6, characterized in that the phosphating solution has a pH in the range from 2.5 to 3.8, a free acid content in the range from 0 to 2.5 points and a content of total acid in the range of 15 to 30 points,

8. The method according to one or more of claims 1 to 7, characterized in that the at least one further parameter characteristic of the phosphating is selected from: the material or the material mixture of the metal surface, the expected value for the total size of the metal surface, between the straight Sub-step b) and the next planned execution of the

Sub-step b) will be brought into contact with the phosphating solution, the pH of the phosphating solution, the temperature of the phosphating solution, the speed at which the phosphating solution is immersed or

Flood process moves relative to the metal surface, the pressure with which the phosphating solution in the case of a spray process on the

Components according to claim 4, the content of the phosphating solution in one or more accelerators other than the accelerator determined in sub-step b).

9. The method according to one or more of claims 1 to 8, characterized in that the start of the sequence of sub-steps b) to e) is carried out by a manually given request.

10. The method according to one or more of claims 1 to 8, characterized in that the start of the sequence of substeps b) to e) after the expiry of a predetermined period of time after the last sub-step b) carried out automatically.

11. The method according to one or more of claims 1 to 8, characterized in that manually or automatically ascertaining at least one result of the phosphating and, in the event of a deviation from a previously specified desired phosphating result, manually or automatically starting the sub-steps b) to e).

12. The method according to claim 11, characterized in that as a result of the phosphating one or more of the following features is determined: the color of the metal surface after contact with the phosphating solution, the uniformity of the phosphate layer, the layer weight of the phosphate layer, the chemical composition of the phosphate layer, the average crystal size or the crystal size distribution in the phosphate layer, the shape of the crystals in the phosphate layer, the electrical impedance of the phosphate layer, the current curve during a cathodic polarization measurement on the phosphate layer, the thickness of a phosphate layer under predetermined deposition conditions

Metal surface deposited layer of a cathodic electrodeposition lacquer, the behavior of the phosphate layer coated with a lacquer in a

Paint adhesion and / or corrosion protection test, the electrical loss potential of the substrate in the phosphating solution.

13. The method according to one or more of claims 1 to 12, characterized in that in addition the turbidity or the sludge content of the phosphating solution is determined and in step e) the (selected) accelerator is metered into the phosphating bath more slowly, the greater the turbidity or Are sludge content.