EP1623054A1

EP1623054A1 - Method for coating metal bodies with a phosphating solution and phosphating solution

Info

Publication number: EP1623054A1
Application number: EP04731327A
Authority: EP
Inventors: Ralf Schneider; Klaus-Dieter Nittel
Original assignee: Chemetall GmbH
Current assignee: Chemetall GmbH
Priority date: 2003-05-06
Filing date: 2004-05-06
Publication date: 2006-02-08
Also published as: MXPA05011817A; DE10320313B4; US20060237099A1; DE10320313A1; JP2006525424A; WO2004099468A1

Abstract

The invention relates to a method for coating surfaces of metal objects, especially as a pre-treatment for cold deformation or as a pre-treatment for a metal-rubber compound or to adjust friction coefficients in connection elements, used in connection elements such as screws for screwing purposes. The invention is characterised in that the optionally, already pre-coated metal objects are coated with a composition containing an aqueous, acidic phosphate, said composition containing 8 - 50 g/L phosphate as PO4, 0.5 - 30 g/L zinc ions, 0 - 5 g/L manganese ions, 0 - 8 g/L calcium ions, 0 - 5 g/L magnesium ions, whereby at least 0.1 g/L of calcium or/and magnesium ions are provided, 0.1 - 5 g/L nitroguanidine, 0.1 - 8 g/L chlorate or/and peroxide ions and 0 - 16 g/L complex fluoride (MeF4 or/and MeF6) of Me = B, Si, Ti, Hf or/and Zr and 0 - 5 g/L fluoride ions, whereby the total amount of complex fluoride and fluoride ions ranges from 0.1 - 18 g/L. The invention also relates to a phosphating method wherein the ratio of removal by pickling in relation to the layer weight of the phosphate layer is less than 75 % . The invention further relates to a corresponding aqueous phosphating solution.

Description

Process for coating metallic bodies with a phosphating solution and the phosphating solution

The present invention relates to a method for phosphating metallic bodies, in particular as a pretreatment for cold forming, as a pretreatment for a metal-rubber compound or for setting friction coefficients for the connection in the case of metallic connecting elements which are in themselves finished.

The formation of phosphate layers on metallic objects has been used for decades with quite different compositions. These coatings primarily serve as protection against corrosion and to increase the adhesive strength of a subsequent layer, e.g. a layer of paint. The phosphate layer often has a layer thickness of approximately 2 to approximately 30 μm.

For the cold forming, the metallic bodies to be formed are often coated with one to four layers of mostly different compositions, so that the cold forming and in particular the wire drawing, extrusion or pipe drawing with significantly reduced friction, significantly less force, significantly less wear on the forming body and the device, become clear reduced expenditure of time and with optimized surface qualities of the formed body can take place. Often a layer sequence of a phosphate and a soap layer e.g. selected from metal stearates. The phosphate layer typically has a layer thickness of approximately 2 to approximately 20 μm. Mostly, phosphate layers based on the phosphates of Zn, ZnMn, ZnCa or ZnFe are used for cold forming.

EP 0 613 964 B1 protects a process for applying a phosphate coating, in which objects made of ferrous materials are immersed in a phosphating solution containing phosphate, zinc, magnesium, fluoroborate and chlorate in certain proportions. No nitrogen-containing compounds should be added to this solution. The chlorate contents of about 3 g / L serve both for acceleration and for the oxidation of Fe ²⁺ to Fe ³⁺ . However, the process has the disadvantages that the phosphating bath requires comparatively high contents of zinc, magnesium, fluoroborate and chlorate and that a relatively high pickling removal and a large volume of sludge are unavoidable. Throughput over two to three days, the sludge volume is often 300 to 500 mg / L. The average edge length of the phosphate crystals thus produced was at least 50 μm.

DE 199 47 232 A1 relates to a method for applying a manganese phosphate layer on iron-containing metallic surfaces, in which zinc-free solutions containing Fe ²⁺ ions, 10 to 25 g / L manganese ions, phosphate ions, 3 to 35 g / L nitrate ions and 0.5 to 5 g / L nitroguanidine can be used.

DE 196 34 685 A1 relates to a method for phosphating metallic surfaces, in which a solution containing phosphate, zinc, nitrate and nitroguanidine is used. However, the solutions are free of alkaline earth ion additives.

DE 38 00 835 A1 teaches a method for phosphating metal surfaces, in which the metal surfaces are contacted without prior activation with a very high content of phosphate, zinc, calcium and at least one accelerator selected from a solution containing nitrate and organic nitro compounds. The calcium and zinc content should be 10 to 40 g / L.

DE 36 36 390 A1 describes a process for the production of phosphate coatings on iron-containing metal surfaces, in which the metallic surfaces are activated without prior activation with a very high content of phosphate, zinc, manganese, nitrate, fluoroborate and tartaric acid and / or citric acid and optionally Contacted urea. The zinc content should be 5 to 25 g / L, the nitrate content 5 to 50 g / L. The disadvantages of this method are that it is used with a very high nitrate content and without self-limitation of the dissolved Fe ²⁺ . No. 4,517,029 protects a process for treating iron-containing metallic surfaces with a phosphating solution which contains 5 to 30 g / L phosphate, 1 to 15 g / L zinc ions, 1 to 3.5 g / L calcium ions and 30 to 50 g / L nitrate ions contains.

The object was therefore to propose a method for phosphating surfaces of metallic objects which is suitable for forming phosphate layers for cold forming, in which the content of sludge which is formed during phosphating can be markedly reduced, if possible without the economy and technical reasons Losing applicability. With the reduction in sludge formation, the chemical consumption during phosphating is also reduced.

In addition, the task was to propose a method for phosphating surfaces of metallic objects that is as environmentally friendly as possible, so that the contents of heavy metals, nitrate, nitrite and other nitrogen-containing compounds can be kept low.

The object is achieved with a method for coating surfaces of metallic objects, in particular as a pretreatment for cold forming or as a pretreatment for a metal-rubber composite or for setting friction coefficients in connection elements for the use of these connection elements, e.g. Screws for screwing, which is characterized in that the possibly already pre-coated metallic objects are coated with an aqueous, acidic, phosphate-containing composition which

8 to 50 g / L phosphate calculated as P0 ₄ , 0.5 to 30 g / L zinc ions, 0 to 5 g / L manganese ions,

0 to 8 g / L calcium ions, 0 to 5 g / L magnesium ions, at least 0.1 g / L of calcium and / or magnesium ions being present, 0.1 to 5 g / L nitroguanidine, 0.1 to 10 g / L total of chlorate and / or peroxide ions, total 0 to 16 g / L complex fluoride (MeF ₄ or / and MeF ₆ ) of Me = B, Si, Ti, Hf or / and Zr and

0 to 5 g / L of fluoride ions, the total content of complex fluoride and fluoride ions being in the range of 0.1 to 18 g / L,

contains.

The phosphate content is preferably 9.5 to 42 g / L, particularly preferably 11 to 34 g / L, very particularly preferably 12 to 28 g / L, in particular 13 to 22 g / L, especially at least 14 g / L or at least 15 g / L or up to 20 g / L or up to 18 g / L.

The zinc ion content is preferably 0.8 to 24 g / L, particularly preferably 1 to 18 g / L, very particularly preferably 1.5 to 12 g / L, in particular 2 to 8 g / L. The zinc content of the cold-forming composition is preferably in the range from 2.5 to 28 g / L, in particular from 5 to 25 g / L. In some cases the zinc content can also be reduced to values in the range of 1.5 ± 1 g / L.

The manganese ion content is preferably 0.05 to 4.5 g / L, particularly preferably 0.1 to 4 g / L, very particularly preferably 0.2 to 3 g / L, in particular 0.3 to 2 g / L. The composition according to the invention preferably has zinc and manganese ions in a ratio of Zn: Mn in the range from 40: 1 to 1: 2, particularly preferably in a ratio of 30: 1 to 1: 1, very particularly preferably in a ratio of 20: 1 to 1.5: 1, in particular in a ratio of 10: 1 to 2: 1.

Preferably, no nickel or only a small amount of nickel is added to the composition, while part or all of the nickel content may be produced by the pickling effect on a nickel-containing metal surface. Because nickel is one of the toxic and environmentally unfriendly heavy metals. On the other hand, it is often advantageous to find or add at least a small amount. The composition then preferably contains nickel ions in the - O -

Range from 0.01 to 2 g / L, particularly preferably 0.05 to 1.5 g / L, very particularly preferably 0.1 to 1 g / L, in particular only up to 0.8 g / L or up to 0 , 5 g / L.

The composition according to the invention preferably has phosphate and zinc in a ratio of PO: Zn in the range from 40: 1 to 1: 1, particularly preferably in a ratio of 30: 1 to 1.5: 1, very particularly preferably in a ratio of 20: 1 to 2: 1, especially in a ratio of 10: 1 to 3: 1.

The content of dissolved Fe ²⁺ ions is preferably reduced to less than 5 g / L, particularly preferred to less than 4 g / L, particularly preferred to less than 3 g / L, especially to limited to less than 2 g / L, 1, 5 g / L or 1 g / L. Above 4 g / L, problems may arise due to the formation of coarse phosphate crystals, which lead to rough instead of smooth phosphated surfaces. In many cases it will therefore be preferred to limit the content of dissolved Fe ⁺ ions to less than 2.5 g / L or even less, in particular in order to enable fine-grained layer formation with a smooth surface.

The calcium ion content is preferably 0.05 to 6 g / L, particularly preferably 0.1 to 5 g / L, very particularly preferably 0.15 to 4 g / L, in particular up to 3 g / L, up to 2 g / L or up to 1 g / L. A calcium ion content may help reduce the amount of sludge formed in the bath by precipitation, may aid in the formation of Ca and Zn-containing phosphate, and / or may reduce or suppress the formation of ZnFe-containing phosphate.

The content of magnesium ions is preferably 0.05 to 4 g / L, particularly preferably 0.1 to 3 g / L, very particularly preferably 0.15 to 2 g / L, in particular up to 1 g / L. A magnesium ion content can help to make the phosphate crystals more fine-grained.

The composition according to the invention preferably has magnesium and calcium ions with a content of at least 0.1 g / L or at least 0.2 g / L in each case and / or in a ratio of Mg: Ca in the range from 40: 1 to 1: 2, especially from 30: 1 to 1: 1, 5, especially from 3: 1 to 1: 1 _ _

The total content of magnesium and calcium ions is preferably 0.15 to 10 g / L, particularly preferably 0.2 to 8 g / L, very particularly preferably 0.25 to 6 g / L, in particular up to 5 g / L, up to 4 g / L, up to 3 g / L or up to 2 g / L.

With an increased content of magnesium fluoride in the solution, the bath can, however, in individual cases get into a thixotropic gel-like state due to, in particular, complex magnesium compounds. The addition of boric acid and / or other boron compounds can then help to lower the free fluoride content in the bath, in order to help avoid larger disruptive contents of such complex magnesium compounds.

The sludge can often be caused by the content of alkaline earths, e.g. Ca, possibly in connection with nitroguanidine, can be brought into a manageable, soft, well compactible and easily rinsable sludge mass. As a result, the sludge does not crust on the surfaces of the devices, e.g. Bath containers, hangers, heating devices, boilers and pipes and can be easily removed or removed.

The presence of at least one complex fluoride can be advantageous in particular because of a more uniform pickling attack and may also help to form thicker phosphate layers. The total content of complex fluorides is preferably 0.1 to 6 g / L, particularly preferably 0.2 to 5 g / L, very particularly preferably 0.3 to 4 g / L, in particular up to 3 g / L, up to 2 g / L or up to 1 g / L.

The fluoroborate content is preferably 0.1 to 5 g / L, particularly preferably 0.2 to 4 g / L, very particularly preferably 0.3 to 3 g / L, in particular up to 2 g / L or up to 1 g / L. Alternatively or additionally, in particular a titanium and / or zirconium hexafluoride can be used.

At least one complex fluoride can particularly advantageously be added if the metallic surface is heavily contaminated by oxide coatings and is to be pickled as uniformly as possible. The addition of complex fluoride can lead to somewhat higher layer thicknesses. The composition can preferably contain fluoroborate, in particular in the range from 0.1 to 5 g / L, particularly preferably in the range from 0.2 to 3 g / L. Adding fluoroborate has the advantage that it has a particularly strong pickling effect. Advantageously, the complex fluoride is at least 30% by weight, at least 60% by weight, at least 80% by weight or completely as fluoroborate.

In some cases it may be advantageous, alternatively or in addition to the content of at least one complex fluoride, fluoride ions e.g. add in the form of hydrofluoric acid, preferably 0.05 to 2.5 g / L of fluoride ions, in particular 0.1 to 1.8 g / L, especially 0.2 to 1.5 g / L. The fluoride ion content can preferably be in the range from 0.05 to 2.5 g / L, in particular in the range from 0.1 to 1.8 g / L, especially in the range from 0.3 to 1.5 g / L L. This can be particularly advantageous for the formation of thicker layers or for problems with cleaning the metallic surfaces. From this and to a limited extent from the complex fluoride, a content of free fluoride is derived, which can optionally react chemically with magnesium ions. However, it must be checked whether there are any interfering effects in the presence of magnesium ions and fluoride ions.

The composition contains complex fluoride and / or fluoride ions to calcium ions, preferably in a ratio of (MeF ₄ , MeF ₆ or / and F ^" ): Ca in the range from 0.1: 1 to 10: 1, particularly preferably in the range from 0.3 : 1 to 8: 1, very particularly preferably in the range from 0.5: 1 to 6: 1.

The composition contains complex fluoride and / or fluoride ions to magnesium ions, preferably in a ratio of (MeF ₄ , MeF ₆ or / and F ^" ): Mg in the range from 0.1: 1 to 10: 1, particularly preferably in the range from 0.2 : 1 to 6: 1, very particularly preferably in the range from 0.3: 1 to 4: 1.

Nitroguanidine and corresponding N-containing guanidine compounds serve in particular as accelerators to depolarize the hydrogen, as a result of which nitroguanidine can be converted to aminoguanidine. Aminoguanidine is readily biodegradable and non-toxic. However, the nitroguanidine also seems to passivate the surface well. The content of nitroguanidine is preferably 0.15 to 4.5 g / L, particularly preferably 0.2 to 4 g / L, very particularly preferably 0.25 to 3 g / L, in particular 0.3 to 2.5 g / L, especially to at 2 g / L or up to 1.5 g / L.

Guanidine compounds containing N, although often referred to as accelerators, do not appear to act as accelerators, since they do not appear to oxidize Fe ²⁺ to Fe ³⁺ , but rather act as passivating agents. This means that they differ significantly from the typical misting systems used for phosphating.

The composition preferably contains not more than 1 g / L nitrate calculated as NO ₃ , particularly preferably 0.1 to 0.8 g / L nitrate, in particular 0.3 to 0.6 g / L nitrate, or is largely or entirely free of nitrate. It preferably contains no more than 0.5 g / L nitrite calculated as N0 ₂ or is largely or entirely free of nitrite. A low or very low nitrite content can form from the nitrate content, often less than 0.2 g / L. The lower the nitrate and nitrite content in the phosphating solution, the less the wastewater that arises from the phosphating is polluted.

Preferably, no further N-containing accelerators are added to the aqueous composition in addition to guanidine compounds and optionally in addition to nitrate and / or nitrite. Alternatively, it contains only comparatively low levels of other N-containing accelerators in addition to those just mentioned. It is advantageous if the contents of nitrate, nitrite and NBS ions (nitrobenzenesulfonate, especially with sodium) are each less than 0.8 g / L or less than 0.4 g / L or even less than 0.2 g / L and / or the total content of all N-containing accelerators with the exception of nitroguanidine and related guanidine compounds such as Aminoguanidine is below 2 g / L.

Preferably no chloride or only a small amount of chloride is added, while in most cases the predominant proportion of chloride arises from chlorate. The composition preferably contains chloride ions in the range from 0.05 to 5 g / L, particularly preferably 0.1 to 4.5 g / L, very particularly preferably 0.2 to 4 g / L, very preferably 0.25 to 3 g / L, in particular 0.3 to 2.5 g / L, especially up to 2 g / L or up to 1.5 g / L. A chloride content provides an additional pickling effect.

Chlorate mainly or exclusively serves as an oxidizing agent to limit the content of the Fe ²⁺ dissolved in the aqueous composition by accelerating the precipitation to Fe ³⁺ . The chlorate content can help to work on the iron side, so that an increased, limited content of Fe ²⁺ remains dissolved in the bath instead of being precipitated as Fe ³⁺ . It only serves as a subordinate or not at all as an accelerator. The chlorate content is preferably 0.15 to 7 g / L, particularly preferably 0.2 to 5 g / L, very particularly preferably 0.25 to 4 g / L, in particular up to 3 g / L, up to 2, 2 g / L or up to 1.5 g / L. It is particularly preferred to keep the chlorate content in the range from 0.8 to 2.5 g / L or even in the range from 1 to 2 g / L. On this basis, it can be advantageous to increase the chlorate content approximately and to the extent necessary to oxidize the Fe ²⁺ in the phosphating ^bath in order to achieve rapid precipitation and to limit the content of Fe ²⁺ in the phosphating bath. eg with an increase in throughput.

Preferably no sulfate is added. However, sulfate and / or chloride can be introduced from the pickling bath, in particular due to carryover. up to approx. 3 g / L can be brought in. A certain sulfate and / or chloride content can come from the water used, from other impurities and from carry-over. The chlorate content in the bath forms a chloride content in the bath composition. If the metallic objects that are to be phosphated are not so dirty and rusted, the chloride and / or sulfate content can be sufficient for the required pickling action in the phosphating bath, so that a pickling bath before phosphating can be dispensed with. In this case, it may sometimes be advisable to add a low chloride and / or sulfate content, in particular up to 1 g / L each, to the bath.

The composition can preferably contain sulfate ions in the range from 0.05 to 2 g / L, particularly preferably 0.1 to 1.8 g / L, very particularly preferably 0.15 to 1.6 g / L, very preferably 0.2 up to 1.2 g / L, in particular 0.25 to 1 g / L, especially up to 0.8 g / L or up to 0.6 g / L. The peroxide content is preferably 0.005 to 3.5 g / L, particularly preferably 0.01 to 2 g / L, very particularly preferably 0.02 to 1 g / L, in particular 0.03 to 0.5 g / L, especially up to 0.2 g / L or up to 0.1 g / L. Peroxide can serve to limit the Fe ²⁺ content in the phosphating solution and as an accelerator.

In addition, a content of alkali and / or ammonium ions can be contained, in particular by adding potassium or / and sodium compounds such as e.g. Sodium chlorate.

Furthermore, a content of at least one pickling inhibitor can be added to the bath solution according to the invention, preferably 0.005 to 0.8 g / L, all pickling inhibitors, particularly preferably 0.01 to 0.6 g / L, very particularly preferably 0.015 to 0.4 g / L. The content of the individual pickling inhibitor is preferably in the range from 0.005 to 0.6 g / L, particularly preferably 0.01 to 0.5 g / L, very particularly preferably 0.015 to 0.4 g / L. In comparison, the concentrate can have the same lower limits as here for the bath solution, but can have twice the upper limits as for the bath solution. In particular, at least one amide, amine, imide and / or imine can be added as pickling inhibitors, for example dimethylaminopropylamine. Such an addition is particularly advantageous for reducing the consumption of the at least one guanidine compound.

The phosphating solution according to the invention can in particular have one of the following compositions:

A) 8 to 30 g / L phosphate calculated as P0 ₄ ,

0.5 to 4.5 g / L zinc ions,

0 to 4 g / L manganese ions, 0 to 8 g / L calcium ions,

0 to 5 g / L of magnesium ions, at least 0.1 g / L of calcium and / or magnesium ions being present,

0.1 to 5 g / L nitroguanidine, 0.1 to 8 g / L total of chlorate and / or peroxide ions, _ _

a total of 0 to 6 g / L of complex fluoride (MeF ₄ and MeF ₆ ) of Me = B, Si, Ti, Hf or / and Zr, which contains fluoroborate, and 0 to 4 g / L of fluoride ions

or B) 8 to 30 g / L phosphate calculated as PO ₄ ,

0.5 to 8 g / L zinc ions,

0 to 5 g / L manganese ions,

0.1 to 8 g / L calcium ions,

0 to 5 g / L magnesium ions, 0.1 to 5 g / L nitroguanidine,

0.1 to 8 g / L total of chlorate and / or peroxide ions, total 0 to 6 g / L complex fluoride (MeF ₄ and MeF ₆ ) of Me = B, Si,

Ti, Hf and / or Zr, containing fluoroborate, and

0 to 4 g / L fluoride ions.

Higher levels of heavy metals should be avoided if possible for reasons of environmental protection. In addition, higher levels of AI, Cr and Pb usually interfere with phosphating. Advantageously, the phosphating solution according to the invention is essentially free or free of contents of Al, Cd, Co, Cr, Cu, Mo, V or / and W. For reasons of environmental protection, the contents of accelerators containing nitrogen apart from nitroguanidine should be kept as low as possible. in particular the nitrate and nitrite contents. Preferably, substantially no or no other nitrogen compound other than at least one guanidine compound is added.

Preferably, all of the compounds present in the bath are readily soluble in water or largely or completely dissolved in water. It is particularly preferred that all bath components, apart from the precipitation products, are readily soluble in water and are well dissolved in water.

The pH of the composition can advantageously be kept in the range from 0.1 to 4, particularly preferably in the range from 0.5 to 3.5, very particularly preferably in the range from 1 to 3. In principle, the pH can be adjusted any suitable substance can be added; zinc carbonate, on the one hand, and, for example, phosphoric acid, on the other hand, are particularly suitable. The total acid value is preferably in the range from 32 to 45 points, in particular from 36 to 40 points, and the free acid value is preferably in the range from 5 to 8 points, in particular from 6 to 7 points. The ratio of the total acid to the value of the free acid, the so-called S value, is preferably in the range from 0.1 to 0.4, particularly preferably in the range from 0.14 to 0.36, very particularly preferably in the range from 0, 18 to 0.32.

The total acid score is determined by titrating 10 ml of the phosphating solution after dilution with water to about 50 ml using phenolphthalein as an indicator until the color changes from colorless to red. The number of ml of 0.1 N sodium hydroxide solution used for this gives the total acidity score. Other indicators suitable for titration are thymolphthalein and ortho-cresolphthalein.

The free acid score is determined in a corresponding manner, using dimethyl yellow as the indicator and titrating until the color changes from pink to yellow.

The S value is defined as the ratio of free P ₂ 0 ₅ to the total content of P ₂ 0 ₅ and can be determined as the ratio of the free acid score to the Fischer total acid score. Fischer total acidity is determined using the titrated sample of the free acid titration and adding 25 ml of 30% potassium oxalate solution and approximately 15 drops of phenolphthalein to it, zeroing the titrator, reducing the free acid score is subtracted and titrated to change from yellow to red. The number of ml of 0.1 n sodium hydroxide solution used for this gives the total acidity of Fischer.

The temperature of the phosphating solution is preferably in the range from 50 to

Maintained at 80 ° C, especially at 55 to 75 ° C. However, the phosphating bath can also be used at other temperatures, for example at temperatures down to about 15 ° C. With short throughput times such as 10 to 30 In seconds, a high concentration and a high temperature of the phosphating solution is recommended.

The phosphating time can be varied within a wide range. In particular, the time of contacting the metallic surface with the phosphating solution is in the range from 1 second to 30 minutes, preferably at least 10 seconds, but in most applications at least 1 or at least 2 minutes. Wire in particular can be phosphated in a rapid pass, e.g. at less than 1 minute.

The phosphate layer formed with the method according to the invention preferably contains Zn, ZnMn, ZnFe, ZnCa and / or CaZn phosphates as phosphates, with a content of calcium in particular hopeit and / or scholzite.

A phosphate layer is preferably formed which has a layer thickness in the range from 0.02 to 15 μm or / and a layer weight in the range from 0.5 to 25 g / m ² , particularly preferably with a layer thickness in the range from 0.05 to 13.5 μm, very particularly preferably with a layer thickness of at least 0.08 μm, in particular of at least 0.12 μm or of up to 11 μm. With the composition according to the invention it is possible to form phosphate layers of extraordinarily different layer thicknesses. On the one hand, it can be advantageous, for example for cold forming, to form phosphate layers with a layer weight in the range from 1.5 to 18 g / m ² - for pipes in particular in the range from 1.5 to 6 g / m ² , for wire in particular in the range from 1.5 to 10 g / m ² or in the case of cold massive forming, for example of bolts and washers, in particular in the range from 3 to 18 g / m ² . On the other hand, phosphate layers with a layer weight in the range from 1.5 to 12 g / m ^{2 can be} advantageous, for example, for the coating of connecting elements such as rivets and screws. If the phosphate layers are to be used as a pretreatment for a metal-rubber composite, it can be advantageous to form layer thicknesses with a layer weight in the range from 0.5 to 3 g / m ² .

The phosphate layers which are used for the cold forming according to the prior art typically have edge lengths of the phosphate crystals in the Order of magnitude around 200 μm. In contrast, in the method according to the invention, decidedly smaller phosphate crystals are formed. However, if the phosphate layers are to be finely crystalline (average edge length of the phosphate crystals approximately in the range from 2 to 25 μm) and, if possible, also with a visual impression of approximately the same crystal size and approximately uniform layer thickness, it may be advisable to apply layer thicknesses with a layer weight in the range of 1 To train 5 to 12 g / m ² . For thick layers in particular, it may be advantageous or even necessary not to form an activation layer before phosphating in order to set layer thicknesses of more than 7.5 g / m ² , in particular more than 10 g / m ² . In most cases, however, the thick phosphate layers will be rather medium or coarse-crystalline, whereby average edge lengths in the range from 25 to 300 μm are often formed - determined using the edge length of the phosphate crystals from scanning electronic images at an angle or perpendicular to the phosphated surface. However, the layer thicknesses or their layer weights are also dependent on the metallic substrate selected. Surprisingly, even phosphate layers with a low layer weight could be formed very well and with very low frictional forces during cold extrusion, especially if the average edge length of the phosphate crystals was less than 10 μm. So far, so-called layer-forming phosphating is obviously always carried out.

In the method according to the invention, a phosphate layer can be formed which has an average edge length of the phosphate crystals of less than 20 μm or even less than 10 μm and often at the same time a layer thickness with a layer weight in the range 1.5 to 18 g / m ² , in particular in the range of 2 to 15 g / m ² .

The object is also achieved with a method for coating surfaces of metallic objects with a phosphating solution, in which the ratio of pickling removal on the metallic surface measured in g / m ² to the layer weight of the phosphate layer measured in g / m ² is below 75% , in particular below 72%, preferably below 68%, particularly preferably below 65%, very particularly preferably below 62% or below 58%. - 10 -

The phosphate layer can serve as an adhesion promoter e.g. for soap, lubricious polymers or other lubricants or corresponding mixtures that are subsequently applied to the phosphate layer and result in a lubricant layer, in particular for wires, tubes, round blanks, disks, rods or other shaped bodies for cold forming. In many cases, the friction alone cannot be reduced sufficiently for cold forming with a single lubricant layer, so that at least one further lubricant layer is then applied. The phosphate layer can e.g. be applied to screws for screwing, so that the coefficient of friction when screwing in is reduced, especially when screwing in automatically, so that the automatic screwdriver can be adjusted according to the torque, which in most cases must not be too high or too low. The screws are mainly heavy-duty screws.

The phosphate layer can be on surfaces of metallic objects such as e.g. Bolts, wires, pipes, washers, rods or preformed metallic bodies, which may also have a complex geometry, can be applied. The phosphate layer according to the invention is particularly suitable for precoating for a metal-rubber composite because it can also be applied very thinly - for example in the range from 0.1 to 5 μm - and because it can be designed to be particularly adhesive.

In principle, all metallic materials can be used as materials that are coated on the surface of such objects, in particular iron-rich alloys such as Steels, galvanized steel and other zinc-containing surfaces.

Before phosphating, the metallic surfaces, in particular depending on the type and degree of soiling, can be cleaned alkaline and / or acidic and / or acid-pickled. In between and / or afterwards there can be at least one rinsing step with water. Alternatively or additionally, the metallic surfaces can optionally be precoated at least once before phosphating, for example with an activation solution and / or with a chemically different _

the subsequent phosphating composite pretreatment composition.

It is advantageous here if the material of the metallic surface of moldings for cold forming can be readily pickled and pickled before coating with the phosphate composition according to the invention, in particular with dilute mineral acids or specific acid-rich mixtures. Alternatively, the metallic surfaces to be coated can be contaminated only slightly, almost not at all, or not at all, so that the pickling action of the phosphating solution is sufficient only for the remaining cleaning of the surface.

In many cases, the pickling effect of the phosphating bath should rather not be very strong in order to limit the amount of sludge that is produced in the phosphating bath.

In many cases it is advantageous if the metallic surfaces are activated before phosphating, e.g. B. with a titanium-containing activation or an activation based on pyrophosphate. In the method according to the invention, however, it is usually not necessary to carry out an activation. Activation usually makes it possible to set an even finer grain of phosphate. An average edge length of the phosphate crystals of less than 30 μm, in particular less than 20 μm, particularly preferably less than 10 μm, less than 5 μm or even less than 2.5 μm, is advantageously produced without or with prior activation. Phosphate crystals with an average edge length of less than 2.5 μm were achieved with a phosphating solution with 0.2 to 0.8 g / L nitroguanidine content after prior activation.

The coating according to the invention is used in particular to prepare for cold forming, in that the coating according to the invention is applied before applying a layer containing a lubricant, such as a composition based on metal istearate (s). The coating for phosphating can in principle also be used in order to achieve corrosion protection and / or adhesion promotion, in particular as a treatment or as a pretreatment for. B. before a subsequent painting. It can also serve as a pretreatment for a metal-rubber composite or for adjusting Friction coefficients in connection elements for using these connection elements, such as screws for screwing.

The metallic object coated according to the invention can be used in cold forming, for a metal-rubber composite, as a connecting element with adjusted friction coefficients or as an element in construction, in vehicle construction, in apparatus construction or in mechanical engineering.

The object is also achieved with an aqueous phosphating solution which serves as a concentrate, as a bath solution and / or as a supplementary solution and which

8 to 100 g / L phosphate calculated as P0 ₄ , 0.5 to 60 g / L zinc ions,

0 to 10 g / L manganese ions,

0 to 16 g / L calcium ions,

0 to 10 g / L magnesium ions, at least 0.1 g / L of calcium and / or magnesium ions being present,

0.05 to 10 g / L nitroguanidine,

0 to 2 g / L nitrate,

0.1 to 10 g / L total of chlorate and / or peroxide ions, total 0 to 16 g / L complex fluoride (MeF ₄ and MeF ₆ ) of Me = B, Si, Ti, Hf or / and Zr and

0 to 5 g / L of fluoride ions, the total content of complex fluoride and fluoride ions being in the range of 0.1 to 18 g / L.

As bath or / and as a supplementary solution, it preferably also contains nitroguanidine, although it may be preferred that nitroguanidine is added separately to the concentrate, to the bath or / and to the supplementary solution. It may be advantageous to add all the components of the bath with the exception of nitroguanidine and / or peroxide in the aqueous phosphating solution, which serves as a concentrate or as a supplementary solution. If nitroguanidine or / and peroxide are contained in the aqueous phosphating solution, their content is preferably at least 0.1 g / L, particularly preferably at least 0.2 g / L each. Alternatively, a supplemental solution can contain chlorate, peroxide and / or zinc in particular. The concentrate is preferably diluted by a factor of 2 to 20 with water to prepare the bath solution.

It was surprising that the addition of nitroguanidine made it possible to create an extremely fine-grained phosphate layer. It was also surprising that the ratio of pickling removal on the metallic surface to the layer weight of the phosphate layer could be reduced to values of up to approximately 47%, which would otherwise be of the order of approximately 80% or even approximately 110% and a correspondingly higher one Condition consumption of phosphate solution. As a result, the consumption could be reduced by a factor of up to about 3. It was also surprising that the addition of nitroguanidine in the presence of alkaline earth ions sometimes produced a sludge that was much easier to handle. The addition of nitroguanidine has surprisingly eliminated the negative effects of the chloride that sometimes occur, possibly increasing the pickling attack and thus increasing the sludge content and consumption. Surprisingly, the amount of sludge formed could be reduced to values of 10 to 50% by weight of other phosphating processes according to the prior art which are used for cold forming. It was also surprising that the addition of nitroguanidine made it possible to set a wide working range for stable phosphating conditions. It was also surprising that the activation upstream made it possible in some cases to set specific layer weights of the phosphate layer.

It seems to be the first time that phosphating has been found that can only be used in a technically particularly advantageous manner with little or no addition of nitrate and / or nitrite and at the same time enables very small phosphate crystals. Finally, it seems that for the first time it has been possible to propose phosphating which, for the first time, allows only a small amount of precipitated sludge to form when phosphate layers are closed.

Examples and comparative examples:

The examples described below are intended to explain the subject matter of the invention in more detail by way of example, without restricting it.

In a first test series, steel sheets made of cold-rolled steel (CRS), welding tubes made of steel and slugs made of carbon-containing steel from 90 to 120 HB 2.5 / 187.5 Brinell hardness were cleaned strongly alkaline, rinsed with cold water, with a titanium activated activating agent activated and then coated in a phosphating bath at 70 ° C. The nitrate- and nitrite-free phosphating bath was prepared with the following starting composition based on water:

20.0 g / L phosphate calculated as PO ₄ , 3.5 g / L zinc ions, 0.3 g / L calcium ions,

0.6 g / L magnesium ions, 0.3 g / L sodium ions, 0 - 4.0 g / L nitroguanidine, 1.0 g / L chlorine ions, 0.9 g / L chloride ions and

0.5 g / L fluoroborate.

No N compound other than nitroguanidine was added. The bathroom was immediately ready for use.

In a first test series, the influence of the nitroguanidine content of the phosphating bath with the above-mentioned starting composition on the bath behavior and the properties of the coating was determined.

Table 1: Properties of the bath and the phosphate layer depending on the addition of nitroguanidine in CRS steel sheets or pipes and slugs Example VB OB 1 B 2 B 3 B 4 B 5

Nitroguanidine additive, g / L 0 0.3 0.5 1 2 4

Pickling removal, g / m ² 4.7 3.5 2.7 2.4 2.0 2.0

Consumption of phospha- approx. 20 n.b. n.d. A n.b. n.d. animal solution%, »A

Sludge volume, mL / L 250 n.b. n.d. 70 n.a. n.d.

Sludge quality hard medium hard soft soft soft soft

Layer weight, g / m ² 9.0 6.8 4.7 3.8 2.8 2.7

Pickling removal: layer 52.2 51, 5 57.5 63.2 71.4 74.1 weight in% average crystal size, μm approx. 60 approx. 20 approx. 2 approx. 3.5 approx. 3.5 approx. 5

Forming behavior after bad good very good very good very good very good Coating with Na soap

The sludge volume was determined with a throughput of 30 standard units NE (1 NE = 0.04 m ² / L) coated metallic surface. The sludge settled particularly firmly on the radiator, especially when there was no or very little nitroguanidine content, but was still - regardless of the nitroguanidine content - easy to rinse off. The layer weight was determined before and after detaching the layer and differential weighing. The mean crystal size was estimated on scanning electron microscope images perpendicular to the phosphate layer. The forming behavior was checked on pipes and slugs. For this purpose, the phosphated bodies to be formed were additionally coated in a conventional manner with a commercially available soap, such as is used for cold forming. Without the addition of nitroguanidine, the phosphate crystals of the phosphate layer became so large that the shaping behavior deteriorated significantly in comparison to the examples according to the invention. The content of dissolved Fe ²⁺ in the phosphating bath, which was approximately zero at the beginning of the work, rose to about 1 g / L during longer work.

Such good phosphating behavior and such good layer properties are

Applicant for phosphating processes according to the state of the art for cold forming is not known: Because fine crystalline phosphate layers from far To the knowledge of the applicant, less than 50 μm average phosphate crystal edge length with less than 75% pickling removal from the layer weight do not belong to the prior art, where, for example, 100 to 120% pickling removal from the layer weight are common in the case of chlorate phosphating processes Nitrite-containing phosphating process 75 to 100% pickling removal; the layer weight according to the prior art is usually in the range from 4 to 12 g / m ² .

The minimum phosphating time for a closed phosphate layer was determined in a second series of experiments. For this purpose, a bath of the starting composition with 0.5 g / L or 1 g / L nitroguanidine was used at 70 ° C. after activation containing titanium.

Table 2: Determination of the layer weights depending on the phosphating time and nitroguanidine content of the phosphating bath on steel sheets made of CRS

The formation of the layer was checked on scanning electron micrographs. The phosphate layer of the bath with 0.5 or 1 g / L nitroguanidine was closed after 5 minutes. In the case of a phosphating bath without the addition of nitroguanidine, after 7 minutes of phosphating time, the layers were almost closed.

In a third test series, the phosphating behavior of a bath with the above-mentioned starting composition was determined for wire rods made of steel containing 0.7% by weight of carbon. The wires were cleaned strongly alkaline, rinsed in water, pickled to remove rust in 15% hydrochloric acid at room temperature for 5 to 10 minutes depending on the degree of rusting until there were no rust deposits, rinsed in water again and pretreated with an activating agent containing titanium. before the wire rods were phosphated. Table 3: Properties of the bath and the phosphate layer depending on the addition of nitroguanidine to wire rod

Example VB 10 B 11 B 12 B 13 B 14 B 15

Nitroguanidine additive, g / L 0 0.3 0.5 1 2 4

Pickling removal, g / m ² 4.2 4.0 3.9 3.9 2.7 2.8

Layer weight, g / m ² 6.4 6.3 6.9 6.8 4.8 4.4

Pickling removal: shift 65.6 63.5 56.5 57.4 56.3 63.6 weight in%

Because of the different rust content of the wire rods and because of the different pickling times, there were greater fluctuations in the measurement results. Due to the increased pickling removal in the phosphating bath without nitroguanidine content, a significantly higher sludge volume is to be expected than in the presence of nitroguanidine, since the sludge volume is proportional to the pickling removal. In this series of experiments, too, the nitroguanidine-containing phosphating baths behave significantly better than the nitroguanidine-free bath.

In a fourth and fifth series of tests, steel sheets made from cold-rolled steel (CRS) were cleaned in a strongly alkaline manner, rinsed with cold water, activated with an activating agent containing titanium and then coated in a phosphating bath at 70 ° C. The phosphating bath A) or B) was prepared with the following starting composition based on water:

A) 24.0 g / L phosphate calculated as PO,

6.0 g / L zinc ions,

0.2 g / L nickel ions, 0 - 5 g / L calcium ions,

0.1 g / L magnesium ions,

3.9 g / L sodium ions,

1.0 g / L nitroguanidine,

0.4 g / L nitrate ions, 0 g / L nitrate ions, 6.0 g / L chlorine ions, 0.4 - 9 g / L chloride ions and 0.4 g / L fluoroborate

respectively.

B) 20.0 g / L phosphate calculated as P0 ₄ , 3.5 g / L zinc ions, 0.3 g / L calcium ions, 0.6 g / L magnesium ions, 0.3 g / L sodium ions, 1.0 g / L nitroguanidine,

0 g / L nitrate ions, 0 g / L nitrate ions, 1 - 11 g / L chlorate ions, 0.5 - 1, 5 g / L chloride ions and 0.5 g / L fluoroborate.

No N compound other than nitroguanidine or, in the case of A), nitrate was added. Baths A) and B) were also immediately ready for use, which is not a matter of course for phosphating baths.

Table 4: Properties of bath A) or B) and the phosphate layer depending on the calcium or chlorate addition

Example VB 16 B 17 B 18 VB 19 B 20 VB 21

Bad A) A) A) A) B) B)

Calcium content, g / L 0 0 1 5 0.3 0.3

Chlorate content, g / L 6 6 6 6 1.5 11

Nitroguanidine content, g / L 0 1 1 1 1 1

Pickling removal, g / m ² 1.9 1.7 1, 8 3.4 1.5 3.2

Layer weight, g / m ² 4.0 3.0 2.9 2.7 3.2 2.6

Pickling removal shift 47.5 56.7 62.0 126 46.9 123 weight in% _ _

With the phosphating bath A), in the fresh state of the calcium-free bath, which initially contained only 0.4 g / L of chloride, there was a small pickling removal and a comparatively low layer weight, but without a content of nitroguanidine, a voluminous sludge and a high one were found sludge content. Over time, the chloride content increased somewhat due to the high addition of chlorate. Pickling removal and layer weight were also reduced. The addition of nitroguanidine reduced the sludge volume, the phosphating bath was clearer and the average edge length of the phosphate crystals was somewhat reduced. The addition of nitroguanidine and calcium chloride significantly increased the chloride content, the sludge was precipitated more compactly, thus significantly reducing the sludge volume and also reducing the average edge length of the phosphate crystals to significantly less than 5 μm. At the same time, however, the ratio of pickling removal to layer weight increased to very high values due to the addition of calcium chloride instead of calcium hydroxide, since the chloride content was increased too much compared to the starting bath composition.

In the case of the phosphating bath B), too, there was an unfavorable ratio of pickling removal to layer weight in the fresh state of the bath because the chlorate content was chosen too high. However, with a chlorate content in the range from 0.2 to 6 g / L, the phosphating bath B) could be used well and with a favorable ratio of pickling removal to layer weight. A chlorate content in the range of 0.5 to 2 g / L was sufficient, since this was able to limit the iron content dissolved in the bath. A slightly higher chlorate content did not interfere, but was not necessary. The chloride content of the bath could then be kept correspondingly low and, with good activation and a nitroguanidine content in the range from 0.2 to 1.8 g / L, almost always resulted in an average edge length of the phosphate crystals of less than 5 μm. With a chlorate content of 11 g / L, the pickling removal was higher than the layer weight, and the phosphate layers were iridescent blue and very thin.

In a sixth series of tests, steel sheets made from cold-rolled steel (CRS) were cleaned in a strongly alkaline manner, rinsed with cold water, with a titanium-containing one

Activating agent activated and then in the phosphating bath at 60 to 70 ° C. Dip coated over 5 to 10 minutes. The phosphating bath was prepared with the following starting composition based on water:

20.0 g / L phosphate calculated as P0 ₄ , 4.0 g / L zinc ions, 0 g / L manganese ions,

0 g / L nickel ions, 0.3 g / L calcium ions, 0.6 g / L magnesium ions, 1.6 g / L sodium ions, 0 - 1 g / L nitroguanidine,

0 g / L nitrate ions, 0 g / L nitrate ions, 0.5 - 1 g / L chlorate ions, 0.1 - 2 g / L chloride ions, 0.8 g / L fluoroborate and

0.2 g / L fluoride ions.

No N compound other than nitroguanidine was added. The bathroom was immediately ready for use. Without a nitroguanidine content, a layer weight of 8 to 10 g / m ² resulted in phosphate layers with an average edge length of the phosphate crystals of more than 50 μm. On the other hand, the addition of 0.3 to 1 g / L nitroguanidine alone made it possible to set phosphate layers with an average edge length of the phosphate crystals in the range from 2 to 10 μm with a layer weight that was varied in the range from 2 to 15 g / m ² , The sludge volume was 50 to 100 mg / L over a period of two to three days.

It was thus found that the process according to the invention can be used particularly advantageously, economically and technically very well. The procedure was simple.

Claims

claims

1. A method for coating surfaces of metallic objects, in particular as a pretreatment for cold forming or as a pretreatment for a metal-rubber composite or for setting friction coefficients in connection elements for use thereof

Fastening elements such as screws for screwing, characterized in that the possibly already pre-coated metallic objects are coated with an aqueous, acidic, phosphate-containing composition which calculates 8 to 50 g / L phosphate as P0 ₄ ,

0.5 to 30 g / L zinc ions, 0 to 5 g / L manganese ions, 0 to 8 g / L calcium ions, 0 to 5 g / L magnesium ions, with at least 0.1 g / L of calcium and / or magnesium ions present are 0.1 to 5 g / L nitroguanidine,

0.1 to 10 g / L total of chlorate and / or peroxide ions, total 0 to 16 g / L complex fluoride (MeF ₄ or / and MeF ₆ ) of Me = B, Si, Ti, Hf or / and Zr and

2. The method according to claim 1, characterized in that the composition contains no more than 1 g / L nitrate or is largely or entirely free of nitrate.

3. The method according to claim 1 or 2, characterized in that the composition contains no more than 0.5 g / L nitrite or is largely or entirely free of nitrite.

4. The method according to any one of the preceding claims, characterized in that the composition complex fluoride and / or fluoride ions to magnesium ions preferably in a ratio of (MeF, MeF ₆ or / and F ^" ): Mg in the range of 0.1: 1 to 10 : 1 contains.

5. The method according to any one of the preceding claims, characterized in that the composition of complex fluoride and / or fluoride ions to calcium ions preferably in a ratio of (MeF, MeF ₆ or / and F ^" ): Ca in the range from 0.1: 1 to 10 : 1 contains.

6. The method according to any one of the preceding claims, characterized in that the composition contains nickel ions in the range up to 2 g / L.

7. The method according to any one of the preceding claims, characterized in that the composition contains chloride ions in the range up to 5 g / L.

8. The method according to any one of the preceding claims, characterized in that the composition contains sulfate ions in the range up to 2 g / L.

9. The method according to any one of the preceding claims, characterized in that the composition contains fluoroborate, in particular in the range from 0.1 to 5 g / L BF ₄ , particularly preferably in the range from 0.2 to 3 g / L.

10. The method according to any one of the preceding claims, characterized in that the pH of the composition is kept in the range from 0.1 to 4.

11. The method according to any one of the preceding claims, characterized in that a phosphate layer is formed with the composition, which has a layer thickness in the range of 0.02 to 15 microns or / and a layer weight in the range of 0.5 to 25 g / m ² having.

12. The method according to any one of the preceding claims, characterized in that a phosphate layer is formed with the composition, which has an average edge length of the phosphate crystals of less than 20 microns or even less than 10 microns and at the same time with a layer thickness has a layer weight in the range from 1.5 to 18 g / m ² , in particular in the range from 2 to 15 g / m ² .

13. The method according to any one of the preceding claims, characterized in that after the formation of the phosphate layer at least one layer containing lubricant is applied.

14. A method for coating surfaces of metallic objects with a phosphating solution, characterized in that the ratio of pickling removal on the metallic surface measured in g / m ² to the layer weight of the phosphate layer measured in g / m ² is below 75%.

15. Aqueous phosphating solution which serves as a concentrate, as a bath or / and as a supplementary solution and which

8 to 100 g / L phosphate calculated as P0 ₄ , 0.5 to 60 g / L zinc ions, 0 to 10 g / L manganese ions,

0 to 16 g / L calcium ions, 0 to 10 g / L magnesium ions, at least 0.1 g / L of calcium and / or magnesium ions being present, 0.05 to 10 g / L nitroguanidine,

0 to 2 g / L nitrate,

0.1 to 10 g / L total of chlorate and / or peroxide ions, total 0 to 16 g / L complex fluoride (MeF ₄ or / and MeF ₆ ) of Me = B, Si, Ti, Hf or / and Zr and 0 up to 5 g / L of fluoride ions, the total content of complex fluoride and fluoride ions being in the range from 0.1 to 18 g / L. _ _

16. Use a metallic object coated with a

Composition according to one of the preceding claims in the

Cold forming, for a metal-rubber composite, as connecting elements with adjusted friction coefficients or as an element in construction, in vehicle construction, in apparatus construction or in mechanical engineering.