Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/82—After-treatment
  • C23C22/83—Chemical after-treatment

Definitions

• the invention relates to methods for phosphating metal surfaces with aqueous, acidic zinc-containing phosphating solutions.
• a rinse with a solution containing lithium, Contains copper and / or silver ions is suitable as a pretreatment of the metal surfaces for a subsequent Painting, especially an electro dip painting.
• the procedure is applicable for the treatment of surfaces made of steel, galvanized or galvanized steel, aluminum, aluminized or alloy aluminized Steel.
• the phosphating of metals pursues the goal on the metal surface to produce firmly adherent metal phosphate layers already improve the corrosion resistance and in Connection with paints and other organic coatings too a significant increase in paint adhesion and resistance to Infiltration under corrosion stress contribute.
• Such phosphating processes have been known for a long time.
• the low-zinc phosphating processes are particularly suitable, where the phosphating solutions are comparatively low levels of zinc ions of e.g. B. 0.5 to 2 g / l.
• the weight ratio of phosphate ions to zinc ions which is usually is in the range> 8 and can take values up to 30.
• phosphate layers have disadvantages in that Nickel and nickel compounds from the point of view of environmental protection and occupational hygiene can be classified as critical.
• Low zinc phosphating processes are increasingly being described the too qualitative without using nickel similar high-quality phosphate layers as the nickel-containing processes to lead.
• nitrite and nitrate Concerns have been raised about possible formation of nitrous gases.
• the phosphating of galvanized steel with nickel-free phosphating baths Corrosion protection and insufficient paint adhesion results if the phosphating baths contain larger quantities (> 0.5 g / l) nitrate.
• DE-A-39 20 296 describes a phosphating process that dispenses with nickel and besides zinc and manganese ions Magnesium ions used.
• the phosphating baths described here contain, in addition to 0.2 to 10 g / l nitrate ions, other accelerators acting oxidizing agents selected from nitrite, chlorate or an organic oxidizing agent.
• EP-A-60 716 discloses low-zinc phosphating baths, which are essential cations zinc and Contain manganese and which contain nickel as an optional component can.
• the necessary accelerator is preferred selected from nitrite, m-nitrobenzenesulfonate or hydrogen peroxide.
• Phosphating baths are also described in EP-A-228 151, which contain zinc and manganese as essential cations.
• the phosphating accelerator is selected from nitrite, nitrate, hydrogen peroxide, m-nitrobenzoate or p-nitrophenol.
• the process of applying the phosphating solution on the metal surfaces and / or other process parameters the phosphate layer on the metal surfaces is not complete closed. Rather, there are more or less large ones "Pores” whose area is on the order of 0.5 to 2% of phosphated surface is located in the course of a so-called "Post-passivation” must be closed to be corrosive To leave influences on the metal surfaces no point of attack. Post-passivation further improves the liability of one then applied paint.
• a rinse solution is known from EP-B-410 497 which contains Al, Zr and contains fluoride ions, the solution being a complex mixture Fluoride or as a solution of aluminum hexafluorozirconate can be understood.
• the total amount of these 3 ions is in the range from 0.1 to 2.0 g / l.
• DE-A-21 00 497 relates to a method for electrophoretic Applying paints to ferrous surfaces, doing the job should be solved, white on the ferrous surfaces or apply other bright colors without discoloration.
• This The object is achieved in that the surfaces that have previously been phosphated can be rinsed with copper-containing solutions. Copper concentrations are between for this rinse solution 0.1 and 10 g / l suggested.
• DE-A-34 00 339 describes also a copper-containing rinse solution for phosphated metal surfaces, with copper contents between 0.01 and 10 g / l is worked. It was not observed that this Rinse solutions in connection with different phosphating processes lead to different results.
• Nickel-free phosphating process in connection with a Chrome-free rinsing currently does not reach all body materials used reliably in the automotive industry the requirements for paint adhesion and corrosion protection. Therefore there is still a need for rinse aid solutions that are related with a nickel- and nitrite-free phosphating and one subsequent cathodic electrocoating the requirements corrosion protection and paint adhesion for different substrate materials reliably meet.
• the invention turns the Task, such a combination of methods from a Environmental and occupational safety optimized phosphating processes and a particularly suitable chrome-free rinse before to provide cathodic electrocoating.
• iron (II) in the concentration range mentioned requires an accelerator that does not react to these ions has an oxidizing effect. Hydroxylamine in particular is an example of this to call.
• the phosphating baths are free of nickel and preferably also of Cobalt. This means that these elements or ions the phosphating baths not be added deliberately. However, it is in the Practice does not rule out that such constituents go beyond that Treating material entered in traces in the phosphating baths become. In particular, it cannot be ruled out that at Phosphating of steel coated with zinc-nickel alloys Nickel ions are introduced into the phosphating solution. However is the expectation of the phosphating baths that under technical conditions under the nickel concentration in the baths 0.01 g / l, in particular below 0.0001 g / l. Preferably included the phosphating baths also do not contain oxo anions from halogens.
• accelerators are in the state of the art Technology known as components of zinc phosphating baths. Below are understood substances that are caused by the pickling attack the hydrogen on the metal surface bind chemically so that they themselves are reduced. Oxidizing Accelerators continue to have the effect of pickling Iron (II) ions released on steel surfaces become trivalent Oxidize stage, so that it as iron (III) phosphate can fail.
• the process sequence according to the invention in the phosphating bath usable accelerators were listed above.
• nitrate ions can be used as co-accelerators in quantities of up to 10 g / l be present, which is particularly the case with phosphating of steel surfaces can have a favorable effect.
• the phosphating solution contains as little nitrate as possible.
• Nitrate concentrations of 0.5 g / l should preferably not be exceeded, since at higher nitrate concentrations the risk of a so-called "Speck formation" exists. These are white, crater-like defects in the phosphate layer meant.
• hydroxylamine is an accelerator particularly preferred. Sharing these two accelerators however, is not advisable since hydroxylamine is made of hydrogen peroxide is decomposed. If you put hydrogen peroxide in free or bound form as an accelerator, so are concentrations from 0.005 to 0.02 g / l of hydrogen peroxide are particularly preferred. Here the hydrogen peroxide of the phosphating solution as such be added. However, it is also possible to add hydrogen peroxide use bound form in the form of compounds in the phosphating bath deliver hydrogen peroxide by hydrolysis reactions.
• persalts such as perborates, Percarbonates, peroxosulfates or peroxodisulfates.
• persalts such as perborates, Percarbonates, peroxosulfates or peroxodisulfates.
• ionic peroxides such as Alkali metal peroxides into consideration.
• Hydroxylamine can be used as a free base, as a hydroxylamine complex or in Form of hydroxylammonium salts can be used.
• the hydroxylammonium salt are the sulfates and the phosphates particularly suitable. In the case of the phosphates are due to the preferred solubility preferred the acid salts.
• Hydroxylamine or its compounds are added to the phosphating bath in such quantities that the calculated concentration of free hydroxylamine between 0.1 and 10 g / l, preferably between 0.2 and 6 g / l and in particular is between 0.3 and 2 g / l.
• hydroxylamine as an accelerator on iron surfaces to particularly favorable spherical and / or leads to columnar phosphate crystals.
• the one to be carried out in sub-step b) Rinsing is a post-passivation of such phosphate layers particularly suitable.
• lithium-containing phosphating baths the preferred ones Concentrations of lithium ions in the range from 0.4 to 1 g / l. Phosphating baths, lithium, are particularly preferred as the only monovalent cation. Depending on what you want Ratio of phosphate ions to divalent cations and However, lithium ions may be required to adjust the desired free acid the phosphating baths further basic Add substances. In this case, ammonia is preferably used a, so that the lithium-containing phosphating baths in addition Contain ammonium ions in the range from about 0.5 to about 2 g / l can.
• the use of basic sodium compounds such as in this case sodium hydroxide solution is less preferred because the presence of sodium ions in the lithium-containing phosphating baths the corrosion protection properties of the layers obtained worsened.
• the free acid preferably by adding basic sodium compounds such as sodium carbonate or sodium hydroxide.
• phosphating baths obtained which, in addition to zinc and possibly lithium manganese (II) contain The manganese content of the phosphating bath should are between 0.2 and 4 g / l, since the lower the manganese content positive influence on the corrosion behavior of the phosphate layers is no longer available and with higher manganese contents no more positive effect occurs. Contents between 0.3 and 2 g / l and especially between 0.5 and 1.5 g / l are preferred.
• the zinc content of the phosphating bath is preferably set to values between 0.45 and 2 g / l.
• the current The zinc content of the working bath increases up to 3 g / l.
• the zinc and manganese ions in the phosphating baths is basically irrelevant. It offers itself in particular, as the zinc and / or manganese source, the oxides and / or to use the carbonates.
• iron (II) ions When using the phosphating process on steel surfaces iron dissolves in the form of iron (II) ions. If the phosphating baths do not contain any substances that are have a strong oxidizing effect, the divalent iron mainly goes into Consequence of air oxidation into the trivalent state so that it can precipitate as iron (III) phosphate. Therefore, in the Phosphate baths build up iron (II) contents that are significantly higher than the Laid down containing baths containing oxidizing agents. This is, for example, in the hydroxylamine-containing phosphating baths the case. In this sense, iron (II) concentrations are up to 50 ppm normal, with values up to in the short term in the production process 500 ppm can occur. For the phosphating process according to the invention such iron (II) concentrations are not harmful.
• the weight ratio of phosphate ions to zinc ions in the phosphating baths can vary within a wide range, provided that it is in the range between 3.7 and 30. A weight ratio between 10 and 20 is particularly preferred.
• the total phosphorus content of the phosphating bath is considered to be present in the form of phosphate ions PO 4 3- . Accordingly, the known fact that the pH values of the phosphating baths, which are usually in the range from about 3 to about 3.4, is only neglected in the form of the triple negative at the pH values of the phosphating baths charged anions. At these pH values, it is rather to be expected that the phosphate is present primarily as a single negatively charged dihydrogenphosphate anion, together with smaller amounts of non-associated phosphoric acid and double negatively charged hydrogenphosphate anions.
• the phosphating can be done in spraying, diving or spray diving respectively.
• the exposure times are in the usual range between about 1 and about 4 minutes.
• the temperature of the phosphating solution is in the range between about 40 and about 60 ° C.
• front phosphating are the usual steps in the prior art cleaning and activation, preferably with activation baths containing titanium phosphate.
• the rinse solution used in sub-step b) preferably has a pH in the range of 3.4 to 6 and a temperature in the range from 20 to 50 ° C.
• the concentrations of the cations in the The aqueous solution used in sub-step b) is preferably in the following areas: lithium (I) 0.02 to 2, in particular 0.2 to 1.5 g / l, copper (II) 0.002 to 1 g / l, in particular 0.01 to 0.1 g / l and silver (I) 0.002 to 1 g / l, in particular 0.01 to 0.1 g / l.
• the metal ions mentioned can be used individually or as a mixture with one another available.
• Rinse solutions containing copper (II) are particularly preferred. contain.
• metal ions mentioned in the rinse solution are introduced is irrelevant in principle, as long as guaranteed is that the metal compounds in the concentration ranges mentioned the metal ions are soluble.
• metal connections should with anions that prevent the tendency to corrode known to promote, such as chloride.
• the metal ions are nitrates or as Carboxylates, especially as acetates.
• phosphates also suitable, provided that they are below the selected concentration and pH conditions are soluble. The same applies to sulfates.
• the metal ions of Lithium, copper and / or silver together in the rinse solutions with hexafluorotitanate and / or, particularly preferably, Hexafluoro zirconia It is preferred that the concentrations of the anions mentioned in the range from 100 to 500 ppm lie.
• the sources of the hexafluoro anions mentioned come from them Acids or their acids under the concentration and pH conditions mentioned water-soluble salts, especially their alkali metal and / or ammonium salts. It is particularly cheap Use hexafluoro anions at least partially in the form of their acids and in the acidic solutions basic compounds of lithium, Dissolve copper and / or silver. For example, come here the hydroxides, oxides or carbonates of the metals mentioned in Consideration. By doing this, you avoid the metals together with any interfering anions.
• the pH can if necessary, adjust with ammonia.
• the rinse solutions can also contain the ions of lithium and copper and / or silver together with ions of cerium (III) and / or cerium (IV) included, with the total concentration of cerium ions in the range from 0.01 to 1 g / l.
• the rinse solution can Copper and / or silver also contain aluminum (III) compounds, the concentration of aluminum in the range of 0.01 to 1 g / l lies.
• the aluminum compounds in particular come on the one hand Polyaluminium compounds such as polymer Aluminum hydroxychloride or polymeric aluminum hydroxysulfate in Consideration (WO 92/15724), or else complex aluminum-zirconium fluorides, as they are known for example from EP-B-410 497.
• the metal surfaces phosphated in sub-step a) can Sub-step b) with the rinse solution by spraying, dipping or Spray diving can be brought into contact with the exposure time should be in the range of 0.5 to 10 minutes and preferably about Is 40 to about 120 seconds. Because of the simpler system technology it is preferable to use the rinse solution in the partial step b) sprayed onto the phosphated metal surface in sub-step a).
• Rinsing off the treatment solution after the end of the exposure period and before the subsequent painting is basically not required.
• phosphated metal surfaces rinsed in sub-step b) can be dried and varnished without further rinsing, for example with a powder coating.
• the procedure is however, especially as a pretreatment before a cathodic one Electro dip coating designed.
• the rinse solution from the metal surfaces rinse off preferably with low salt or desalinated Water.
• the metal surfaces pretreated according to the invention are dried. In the interest of a faster production cycle, however, is omitted preferably such drying.
• the cathodic electrodeposition paint FT 85-7042 gray from BASF was used for painting.
• the corrosion protection test was carried out according to the VDA alternating climate test 621-415.
• the paint infiltration at the Ritz is entered in Table 5.
• a paint adhesion test was carried out according to the VW stone impact test, which was assessed according to the K value. Higher K values mean poorer, lower K values better paint adhesion.
• the results are also shown in Table 5.
• Corrosion protection values and paint adhesion parameters Rinse solution Paint infiltration (mm) K value steel galvanized steel steel galvanized steel completely desalinated water 1.8 4 - 5 7-8 9 Compare 4 1.3 3-4 6 8th Ex. P 1.2 6 Ex. Q 1.0 2.5 - 3.5 6 8th Ex. R 1.2 2.1 - 3 6 8th Ex 1.1 6

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• Chemical & Material Sciences (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)
• Chemically Coating (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Removal Of Specific Substances (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)

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• 1995
  • 1995-03-29 DE DE19511573A patent/DE19511573A1/de not_active Withdrawn
• 1996
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