DE19540085A1 - Low nitrate, manganese-free zinc phosphating - Google Patents

Abstract

A process is disclosed for phosphatizing steel, galvanized or alloy galvanized steel and/or aluminium or its alloys by treatment with a zinc phosphatizing solution applied in a dip, spray or spray/dip process. The process is characterized in that the zinc phosphatization solution has a maximum nitrate ion content of 0.5 g/l, is free of manganese, nickel and cobalt ions, contains 0.3-2 g/l zinc ions, 5-40 g/l phosphate ions and one or more accelerators.

Description

The invention relates to a method for phosphating Me tall surfaces with aqueous, acid phosphating solutions, the zinc and phosphate ions and accelerators in free or bound Contain form, and their use as a pretreatment of the Me tall surfaces for subsequent painting, in particular an electro dip painting. The method is applicable for loading treatment of surfaces made of steel, galvanized or alloy galvanized steel, aluminum, aluminized or alloy aluminum steel.

The phosphating of metals pursues the goal on the metal to produce firmly adhered metal phosphate layers, the already improve corrosion resistance and in conjunction with paints and other organic coatings into one substantial increase in liability and resistance to sub contribute to corrosion when exposed to corrosion. Such phospha Animal processes have long been known in the art. For the pretreatment before painting are particularly suitable Low-zinc phosphating processes in which the phosphating solution conditions comparatively low levels of zinc ions of z. B. 0.5 to  Have 2 g / l. An essential parameter in these low Zinc phosphating baths is the weight ratio of phosphate ions to Zinc ions, which is usually in the range <12 and values up to 30 can assume.

It has been shown that by sharing others, more cations than zinc in the phosphating baths with significantly improved corrosion protection and paint adhesion properties can be trained. For example, low Zinc process with the addition of z. B. 0.5 to 1.5 g / l of manganese ions and e.g. B. 0.3 to 2.0 g / l of nickel ions as a so-called trication process for the preparation of metal surfaces for painting, for example for the cathodic electrocoating of Au bodywork, wide application.

DE-A-39 20 296 describes a phosphating process based on Nickel is dispensed with and, in addition to zinc and manganese ions, magnesium ions used. The phosphating baths described here contain except 0.2 to 10 g / l nitrate ions further oxi acting as accelerators dation agent selected from nitrite, chlorate or an organi oxidizing agent. Against the accelerators nitrite and nitrate there are growing concerns about possible formation of nitrous gases voiced.

The phosphating agent disclosed in WO 86/04931 works free of nitrates method. Here the accelerator system is based on a Kombina tion of bromate and m-nitrobenzenesulfonate. As more essential valuable cation is only zinc, as another optional cat Ions of nickel, manganese or cobalt. Preferably included the phosphating solutions in addition to zinc at least 2 of these optional Metals.  

DE-A-40 13 483 discloses phosphating processes with which similar good corrosion protection properties as with the trication ver driving can be achieved. These processes do not use nickel and instead use copper in low concentrations, 0.001 to 0.03 g / l. For the oxidation of the pickling reaction of Steel surfaces formed bivalent iron in the trivalent Stage serves oxygen and / or other equivalent oxidation medium. As such are nitrite, chlorate, bromate, peroxy-verbin and organic nitro compounds, such as nitrobenzenesulfonate, specified. The German patent application DE 42 10 513 modified this process in that as a modifying agent for the Mor phology of the phosphate crystals formed hydroxylamine, the Salts or complexes in an amount of 0.5 to 5 g / l hydroxylamine be added.

The use of hydroxylamine and / or its compounds for Influencing the shape of the phosphate crystals is from a number of Disclosure known. EP-A-315 059 gives as special Effect of using hydroxylamine in phosphating baths The fact that the phosphate crystals in a desired columnar or knot-like shape arise when the zinc concentration in the phosphating bath for low zinc Ver drive exceeds the usual range. This makes it possible to Phosphating baths with zinc concentrations up to 2 g / l and with Ge weight ratios of phosphate to zinc down to 3.7. About advantageous cation combinations of these phosphating baths no further statements are made in the patent examples however, nickel is used in all cases. Also in the Patent examples used nitrates and nitric acid, even if in the description of the presence of nitrate in large quantities is discouraged. The required hydroxylamine concentration will be with 0.5 to 50 g / l, preferably 1 to 10 g / l.  

Trication-phosphating process in which the phosphating solutions Zinc, nickel and manganese ions have been used especially for developed the phosphating of galvanized steel. By the one construction of nickel and manganese in the phosphate layers could parts balanced in terms of paint adhesion and corrosion protection be, which resulted from the fact that on galvanized substrates le only Hopeit, but no phosphophyllite crystals formed will. From the phosphating of non-galvanized steel it is known that phosphophyllite-rich layers compared to hopeit-rich Layering advantages in terms of paint adhesion and corrosion protection Offer. Because galvanized steel is widely used in automotive engineering are currently trication-phosphating for this type area of application widespread. The presence of nickel and Manganese in almost the same concentrations as zinc contributes the wastewater treatment of rinse water to a ver increased formation of sludges containing heavy metals, which are classified as hazardous waste must be disposed of. When reworking phosphate containing nickel layers can also form nickel-containing dusts, which as can be classified as carcinogenic.

Therefore, there has been an effort to phosphate ver driving to develop, where without sacrificing performance on the be particularly critical nickel can be dispensed with. Here was considered, among other things, to make nickel by cobalt replace. At least under wastewater and toxicological However, cobalt is not an alternative to nickel Some documents have already been referred to above sen, in which instead of nickel, for example, magnesium or Copper, the latter in very low concentrations, is used will.

The object of the present invention is now Phos to provide phating procedures that are not only based on the toxicologically questionable metals nickel and cobalt, but manganese is also dispensed with. This can cause the heavy metal content of the sludge resulting from the treatment of the rinse water be significantly reduced. Of course, the new one Phosphating process made the requirement that Phos layers as the basis for subsequent painting have witnessed whose characteristics are not behind those processes containing manganese and especially trication processes lag behind.

This object is achieved by a process for phosphating Steel, galvanized or alloy galvanized steel and / or of Aluminum or its alloys by treating with a zinc phosphating solution in immersion, spray or splash immersion processes, characterized in that the zinc phosphating solution has a maxi paint has a nitrate ion content of 0.5 g / l and is free of Manganese nickel and cobalt ions and that they

0.3 to 2 g / l zinc ions,
5 to 40 g / l phosphate ions

and one or more of the following accelerators:

0.1 to 10 g / l hydroxylamine in free, ionic or complex-bound form,
0.3 to 5 g / l chlorate 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,
0.01 to 10 g / l of a reducing sugar.

That the phosphating baths are free from manganese, nickel and Cobalt ions means that these ions are used in the phosphating baths not be added deliberately. When phosphating metal surfaces that contain these metals as alloy components, However, it cannot be ruled out that ge by the pickling attack ring amounts of the corresponding cations in the phosphating baths reach. This can be the case in particular if with a Zinc-nickel alloy coated steel is phosphated. In the In practice, however, the expectation is placed on the phosphating baths that they contain less than 0.05 g / l of the cations mentioned.

In addition to zinc ions, phosphating baths usually contain sodium, Potassium and / or ammonium ions to adjust the free acid. The term free acid is known to those skilled in the art of phosphating common area. The method of determination chosen in this document the free acid and the total acid is indicated in the example section give. Preferably in the phosphating according to the invention process used phosphating solutions, the other one or contain divalent metal ions because of their chemical egg properties and / or their lower use concentrations are less problematic than nickel and manganese and which is experienced according to the cheap on the paint adhesion and the corrosion protection of the impact phosphate layers produced with it. Accordingly, it is Method according to the invention preferably characterized in that the phosphating solution additionally one or more of the following Cations contains:

0.2 to 2.5 g / l magnesium (II),
0.2 to 2.5 g / l calcium (II),
0.01 to 0.5 g / l iron (II),
0.001 to 0.03 g / l copper (I) and / or copper (II),
0.2 to 1.5 g / l lithium (I),
0.02 to 0.8 g / l tungsten (VI).

The weight ratio of phosphate ions to zinc ions in the phospha Animal baths can fluctuate within wide limits, provided it is in the area is between 3.7 and 30. A weight ratio between 10 and 20 is particularly preferred. As further parameters for controlling Phosphate baths are the free acid and known for total acid. The definition used in this document The method of determining this parameter is given in the example section. values the free acid between about 0.3 and about 1.5 points and the Total acid between about 15 and about 35 points are in the tech nisch usual area and are suitable in the context of this invention net.

When phosphating zinc-containing surfaces, it has proven to be Proven favorable, the nitrate content of the phosphating bath to a maximum Limit 0.5 g / l. This solves the problem of the so-called Suppression of specks and improved corrosion protection. Phosphating baths which are less than 0.05 g / l are particularly preferred and especially contain no nitrate.

For phosphating baths that are suitable for different substrates it has become common to be free and / or complex denes fluoride in amounts up to 2.5 g / l total fluoride, of which up to Add 800 mg / l free fluoride. The presence of such fluo Amounts are also for the phosphating baths of the invention Advantage. In the absence of fluoride, the aluminum content of the Do not exceed 3 mg / l bath. In the presence of fluoride  tolerated higher Al contents due to the complex formation, provided that Concentration of the non-complexed Al does not exceed 3 mg / l.

The accelerators listed above come in the state of the Technology known substances into consideration. These accelerate to one layer formation, since they have a "depolarizing" effect by the ele formed on the metal surface during the pickling attack oxidize mental hydrogen to water. Certain accelerators such as hydroxylamine, however, can also take the form of influence the resulting phosphate crystals. Oxidizing Accelerators continue to cause the pickling reaction Iron (II) ions formed on steel surfaces at the trivalent stage are oxidized so that they precipitate as iron (III) phosphate.

In addition to the accelerators listed above could be in the frame nitrite are also used in the invention. However, this is we niger preferred because the present invention a phospha animal procedure is to be provided, which particularly few to xicological and disposal problems. Under the In terms of occupational safety, however, nitrite is special critical because of its use harmful nitrous gases can arise. Farther could use nitrite through its oxidation to nitrate arise, so that the low nitrate levels according to the invention would step.

The accelerators listed above can be used individually, at chemical compatibility, however, also in combination with each other be used. For example, there is a preferred embodiment tion form of the invention in that in the phosphating in Immersion process a combination of chlorine ions and hydrogen peroxide is used. The hydrogen peroxide can  such d. H. in free form, or also in bound form, at for example as an ionic peroxide or in the form of Peroxo compounds such as peroxosulfuric acid, Carosche Acid or peroxophosphoric acid can be used. As another Sodium per comes as a carrier for hydrogen peroxide in bound form borate into consideration. In this embodiment, the concentration of chlorate, for example in the range of 2 to 4 g / l, the conc tration of hydrogen peroxide are in the range of 10 to 50 ppm.

The use of reducing sugar as an accelerator is out of the question US-A-5 378 292 known. You can within the scope of the present Er invention in amounts between about 0.01 and about 10 g / l, preferably in Amounts between about 0.5 and about 1.5 g / l are used. At games of such sugars are galactose, mannose and in particular Glucose (dextrose).

Another preferred embodiment of the invention is in to use hydroxylamine as an accelerator. Hydroxylamine can as a free base, as a hydroxylamine complex or in the form of hydroxyl ammonium salts are used. If you add free hydroxylamine Phosphating bath or a phosphating bath concentrate too, it will largely due to the acidic nature of these solutions as Hy droxylammonium cation are present. When used as a hydro xylammonium salt, the sulfates and the phosphates are special suitable. In the case of phosphates, due to the better solubility preferred the acidic salts. Hydroxylamine or its ver Bonds are added to the phosphating bath in such quantities that that the calculated concentration of free hydroxylamine between 0.1 and 10 g / l, preferably between 0.3 and 5 g / l. It is preferred that the phosphating baths as the only loading accelerated hydroxylamine, at most together with a maximum of 0.5 g / l Nitrate. Accordingly, in a preferred  Embodiment phosphating baths used, which none of the son known accelerators such as nitrite, Oxo anions of halogens, peroxides or nitrobenzenesulfonate ent hold.

In practice it has been shown that the accelerator is hydroxyl amine can be slowly inactivated even when in the Phos phating bath no metal parts to be phosphated introduced the. It has surprisingly been found that the inactivation of the Hydroxylamine can be slowed down significantly if you take the Phos phating bath additionally one or more aliphatic Hydroxycarboxylic acids with 3 to 6 carbon atoms in one total amount of 0.5 to 1.5 g / l is added. Here are the Hydroxycarboxylic acids preferably selected from lactic acid, Gluconic acid, tartronic acid, malic acid, tartaric acid and citric acid, citric acid is particularly preferred.

The zinc content of the phosphating bath is increased according to EP-A-315 059 Set values between 0.45 and 1.1 g / l. As a result of the pickling contract However, it is in the phosphating of zinc-containing surfaces possible that the current zinc content of the working bath above a value of 1.1 g / l. Zinc levels up to 2 g / l are in Harmless within the scope of the present invention. Depending on the systems technology, zinc contents of up to 2 g / l can also pose a risk Reduce rust formation during phosphating. In which form the cations are introduced into the phosphating baths is prin partially irrelevant. It is particularly useful as cations source oxides and / or carbonates to use.

When using the phosphating process on steel surfaces iron dissolves in the form of iron (II) ions. Since the inventions phosphating baths according to the invention preferably no substances  contain that have an oxidizing effect on iron (II), that works divalent iron only as a result of air oxidation in the trivalent state so that it is called iron (III) phosphate can fall. Therefore, in the phospha according to the invention animal baths build up iron (II) contents that are well above the Ge hold lying, which contain oxidizing agent-containing baths. In in this sense iron (II) concentrations up to 50 ppm are normal, with short-term values up to 500 ppm in the production process may occur. For the phosphating process according to the invention such iron (II) concentrations are not harmful. With approach in hard water, the phosphating baths can continue to be hard Forming cations Mg (II) and Ca (II) in a total concentration of contain up to 7 mmol / l. Mg (II) or Ca (II) can the phospha animal bath can also be added in amounts up to 2.5 g / l.

In a further preferred embodiment, a phospha animal solution used as the only cations with an actual Liche or potential oxidation level of <1 zinc and Contains copper ions. Zinc and copper ions are in the phospha animal solution is usually in oxidation state 2. It is however, it is conceivable that the accelerator, which acts in principle such as hydroxylamine, the copper ions at least partially can reduce to the univalent level. In addition to zinc and Copper ions, this preferred phosphating solution can also contain sodium, Contain potassium and / or ammonium ions, which as usual in the form their basic compounds for adjusting the free acidity of the Phosphating solution may have been used. It is be particularly preferred that the phosphating solution when used in Immersion method 3 to 20 mg / l copper ions, when used in spray procedure contains 1 to 10 mg / l copper ions.  

The temperature of the phosphating solution is preferably in the range between about 40 and about 60 ° C. It has turned out to be more positive Side effect of the phosphating process according to the invention represents that hydroxylamine concentrations above about 1.5 g / l Risk of rust formation in insufficiently flooded areas of the significantly reduce phosphating components.

The process according to the invention is suitable for phosphating Surfaces made of steel, galvanized or alloy galvanized steel, Aluminum, aluminized or alloy-aluminized steel. The ge named materials - as is increasingly the case in automotive engineering It is common to also exist side by side. Parts can the body also consist of pre-treated material, such as the Bonazink® process. Here at the base material is first chromated or phosphated and then coated with an organic resin. The Phosphating process according to the invention then leads to a Phosphating at damaged areas of this pretreatment layer or on untreated backs.

The method can be used in particular in automobile construction, where treatment times between 1 and 8 minutes are common. It is in particular for the treatment of the metal surfaces mentioned a paint job, especially a cathodic one Electro-dip coating thought as it is common in automotive engineering. The phosphating process is a sub-step of the technically usual See pretreatment chain. In this chain are the Phosphating usually the steps cleaning / degreasing, intermediate rinse and activate upstream, the activation usually with titanium phosphate-containing activating agents. The phosphating according to the invention can, if appropriate, after ei After an intermediate rinse, a passivating after-treatment follows. For  such a passivating aftertreatment contains chromic acid Treatment baths widely used. For reasons of work and order environmental protection and for disposal reasons, however, there are ten denz, these chrome-containing passivation baths through chrome-free treatment lungs baths to replace. Purely inorganic baths, ins especially based on zirconium compounds, or orga African baths, for example based on poly (vinylphenols), known. Between this post passivation and the more common wise subsequent electrocoating is usually a Intermediate rinsing with demineralized water.

Embodiments

The phosphating process according to the invention and the comparative process were on electrolytically galvanized steel sheets, as in the Find automotive use, checked. The following, common in body production, process as diving ver drive executed:

• 1.Clean with an alkaline cleaner (Ridoline® 1559, Henkel KGaA), batch 2% in city water, 55 ° C, 4 minutes.
• 2. Rinse with city water, room temperature, 1 minute.
• 3. Activation with an activating agent containing titanium phosphate (Fixodine® C9112, Henkel KGaA), 0.1% batch in fully desalinated Water, room temperature, 1 minute.
• 4. Phosphating with phosphating baths according to Table 1. Temperature 55 ° C. In addition to the cations listed in Table 1, the phosphating baths only contained sodium ions to adjust the free acid. The baths contained no nitrite or nitrate.
  The free acid score is understood to mean the consumption in ml of 0.1 normal sodium hydroxide solution in order to titrate 10 ml of bath solution up to a pH of 3.6. Similarly, the total acid score indicates consumption in ml up to a pH of 8.5.
• 5. Rinse with city water, room temperature, 1 minute.  
• 6. Post-passivation with a chrome-free post-passivation agent based on complex zirconium fluoride (Deoxylyte® 54 NC, Henkel KGaA) 0.25% in deionized water, pH 4.0, temperature 40 ° C, 1 minute.
• 7. Rinse with deionized water.
• 8. Blow dry with compressed air

The mass per unit area ("layer weight") was obtained by peeling off in 5% chromic acid solution determined according to DIN 50942.

The phosphated test panels were dipped with a cathodic paint from BASF (FT 85-7042) coated. The corrosion The protective effect was tested in an alternating climate test according to VDA 621-415 Tested 10 laps. As a result, the paint infiltration at the Ritz (half scratch width) included in Table 1. Table 1 contains also the results of a stone chip test as "K values" VW standard.  

Table 1

Phosphating baths and test results

Claims (11)

1. A method for phosphating steel, galvanized or zinc-alloyed steel and / or aluminum or its alloys by treatment with a zinc phosphating solution in the immersion, spray or spray immersion process, characterized in that the zinc phosphating solution has a maximum nitrate ion content of 0.5 g / l and is free of manganese, nickel and cobalt ions and that it contains 0.3 to 2 g / l zinc ions,
5 to 40 g / l phosphate ions and contains one or more of the following accelerators:
0.1 to 10 g / l hydroxylamine in free, ionic or complex-bound form,
0.3 to 5 g / l chlorate 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
0.01 to 10 g / l of a reducing sugar. 2. The method according to claim 1, characterized in that the phosphating solution additionally contains one or more of the following cations: 0.2 to 2.5 g / l magnesium (II),
0.2 to 2.5 g / l calcium (II),
0.01 to 0.5 g / l iron (II),
0.001 to 0.03 g / l copper (I) and / or copper (II),
0.2 to 1.5 g / l lithium (I),
0.02 to 0.8 g / l tungsten (VI). 3. The method according to one or both of claims 1 and 2, characterized characterized in that the phosphating solution does not exceed Contains 0.05g / l nitrate ions. 4. The method according to one or more of claims 1 to 3, since characterized in that the phosphating solution additionally Fluoride in free and / or complex bound form in quantities up to 2.5 g / l total fluoride, of which up to 0.8 g / l free Contains fluoride. 5. The method according to one or more of claims 1 to 4, because characterized in that the phosphating solution when used a combination of in the immersion process as an accelerator Chlorate ions and hydrogen peroxide in free or bound Contains form. 6. The method according to one or more of claims 1 to 4, since characterized in that the phosphating solution as the only one Accelerator hydroxylamine in a concentration in the range Contains 0.3 to 5 g / l. 7. The method according to claim 6, characterized in that the Phosphating solution additionally one or more aliphatic Hydroxycarboxylic acids with 3 to 6 carbon atoms in a total amount contains from 0.5 to 1.5 g / l.   8. The method according to claim 7, characterized in that the Hydroxycarboxylic acids are selected from lactic acid, Gluconic acid, tartronic acid, malic acid, tartaric acid and Citric acid. 9. The method according to one or more of claims 2 to 8, since characterized in that the phosphating solution is the only one Cations with an actual or potential oxidation contains greater than 1 zinc and copper ions. 10. The method according to claim 9, characterized in that the Phosphating solution when used in the immersion process 3 to 20 mg / l Copper ions, when used in the spray process 1 to 10 mg / l Contains copper ions. 11. Use of the method according to one or more of the claims che 1 to 9 for pretreating the metal surfaces before a Painting.