WO1998048076A1

WO1998048076A1 - Phosphatising process accelerated with hydroxylamine and chlorate

Info

Publication number: WO1998048076A1
Application number: PCT/EP1998/002036
Authority: WO
Inventors: Jan-Willem Brouwer; Jürgen Geke; Peter Kuhm
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1997-04-17
Filing date: 1998-04-08
Publication date: 1998-10-29
Also published as: AU7523098A; DE19716075A1

Abstract

An acid aqueous phosphatising solution contains 0.2 to 3 g/l zinc ions; 3 to 50 g/l phosphate ions, in the form of PO43- as we ll as accelerators, and is characterised in that it contains as accelerators 1 to 4 g/l chlorate ions and 0.1 to 10 g/l free, ionic or bonded hydroxylamine. This phosphatising solution can further contain Mn(II), Mg(II), Ca(II) and/or Cu(II) or Ni(II) as additional cations.

Description

Phosphating process accelerated with hydroxylamine and chlorate

The invention relates to a process for the phosphating of metal surfaces with aqueous, acid phosphating solutions which contain zinc and phosphate ions and hydroxylamine in free or bound form together with chlorate ions, and to their use as pretreatment of the metal surfaces for subsequent painting, in particular electrocoating. The method is applicable for the treatment of surfaces made of steel, galvanized or alloy galvanized steel, aluminum, aluminized or alloy aluminized steel.

The phosphating of metals pursues the goal of producing firmly adherent metal phosphate layers that already improve corrosion resistance and, in conjunction with paints and other organic coatings, contribute to a significant increase in adhesion and resistance to infiltration when exposed to corrosion. Such phosphating processes have long been known in the prior art. For the pretreatment before painting, the low-zinc phosphating processes are particularly suitable, in which the phosphating solutions have comparatively low contents of zinc ions of e.g. B. 0.5 to 2 g / 1. An important 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 can take values up to 30. It has been shown that by using polyvalent cations other than zinc in the phosphating baths, phosphate layers with significantly improved corrosion protection and paint adhesion properties can be formed. For example, find low-zinc processes with the addition of z. B. 0.5 to 1.5 g / l of manganese ions and z. B. 0.3 to 2.0 g / l of nickel ions as a so-called trication process for the preparation of metal surfaces for painting, for example for the cathodic electrodeposition of car bodies, wide application.

DE-A-39 20 296 describes a phosphating process which dispenses with nickel and uses magnesium ions in addition to zinc and manganese ions. The phosphating baths described here contain, in addition to 0.2 to 10 g / l nitrate ions, further oxidizing agents which act as accelerators, selected from nitrite, chlorate or an organic oxidizing agent. Concerns about the accelerators nitrite and nitrate are being raised due to the possible formation of nitrous gases.

DE-A-40 13 483 discloses phosphating processes with which good corrosion protection properties similar to those obtained with the trication processes can be achieved. These processes do without nickel and instead use copper in low concentrations, 0.001 to 0.03 g / l. Oxygen and / or other oxidizing agents with the same effect are used to oxidize the divalent iron formed in the pickling reaction of steel surfaces to the trivalent stage. Nitrite, chlorate, bromate, peroxy compounds and organic nitro compounds such as nitrobenzenesulfonate are specified as such. The German patent application DE 42 10 513 modifies this process by adding hydroxylamine, its salts or complexes in an amount of 0.5 to 5 g / l hydroxylamine as a modifying agent for the morphology of the phosphate crystals formed. The use of hydroxylamine and / or its compounds to influence the shape of the phosphate crystals is known from a number of published publications. EP-A-315 059 specifies the particular effect of the use of hydroxylamine in phosphating baths in the fact that the phosphate crystals are still formed in a desired columnar or knot-like form on steel when the zinc concentration in the phosphating bath corresponds to that for low-zinc Procedure exceeds the usual range. This makes it possible to operate the phosphating baths with zinc concentrations up to 2 g / l and with weight ratios of phosphate to zinc down to 3.7. The required hydroxylamine concentration is given as 0.5 to 50 g / l, preferably 1 to 10 g / l. The phosphating solution is sprayed onto the steel surfaces.

WO 93/03198 teaches the use of hydroxylamine as an accelerator in trication-phosphating baths with zinc contents between 0.5 and 2 g / l and nickel and manganese contents of 0.2 to 1.5 g / l each, with certain weight ratios between Zinc and the other divalent cations are to be observed. Furthermore, these baths contain 1 to 2.5 g / l of a "hydroxylamine accelerator", of which, according to the description, salts of hydroxylamine are preferred

Hydroxylammonium sulfate are to be understood.

Chlorate is widely used as an accelerator in the prior art. For example, EP-B-135 622 describes manganese-containing zinc phosphating solutions which contain a combination of nitrite and chlorate as an accelerator system. In recent times, however, nitrite-free, hydroxylamine-accelerated phosphating processes have become increasingly important. The absence of nitrite makes the formation more nitrous Prevents gases. Compared to nitrite, hydroxylamine has the further advantage of being stable in a phosphating concentrate. The accelerator hydroxylamine can therefore be installed in the supplementary concentrates of the phosphating baths. It is not necessary to add the accelerator solution separately from the supplementary solution.

In contrast to the conventional accelerators, since hydroxylamine is not a strong oxidizing agent, it cannot oxidize the iron (II) ions that dissolve when steel surfaces are phosphated to the trivalent stage in order to precipitate them as iron (III) phosphate. Excessively high levels of iron (II) in the phosphating bath can lead to rust formation on iron surfaces. If hydroxylamine is used as the only accelerator in immersion processes, this can lead to inadequate phosphate layer formation with little bath movement or in poorly flooded areas, for example in the roof area of the body.

The object of the invention is to provide a phosphating process which has the advantages of hydroxylamine-accelerated processes but not the disadvantages thereof. If possible, the use of nitrite should be avoided in order to avoid the formation of nitrous gases. The phosphating process should be applicable in the spray, splash immersion or immersion process.

The invention accordingly relates to an acidic, aqueous phosphating solution containing

0.2 to 3 g / l zinc ions

3 to 50 g / l phosphate ions, calculated as PO ₄ ^{3 "} and accelerator, characterized in that the solution as an accelerator

Contains 1 to 4 g / l chlorate ions and 0.1 to 10 g / l hydroxylamine in free, ionic or bound form.

Surprisingly, the rather reducing hydroxylamine and the oxidizing chlorate do not influence each other in the concentration range mentioned. However, hydroxylamine and chlorate complement each other in their accelerating action. As in chlorate-free phosphating baths, hydroxylamine presumably works by binding the hydrogen that forms on the metal surface during pickling. The simultaneous presence of chlorate leads to the fact that the iron (II) which dissolves when phosphating iron surfaces is oxidized to the trivalent stage and precipitated from the phosphating bath. The formation of rust in poorly flooded areas during immersion processes is suppressed. The chlorate ion content is preferably in the range from about 2 to about 3 g / l.

In addition to zinc ions, phosphating baths generally contain sodium, potassium and / or ammonium ions to adjust the free acid. The phosphating bath according to the invention preferably has a free acid content between 0 and 1.5 points. The term free acid is familiar to the person skilled in the phosphating field. The method of determining free acid and total acid chosen in this document is given in the example section.

Preferably, phosphating solutions are used in the phosphating process according to the invention which contain further mono- or divalent metal ions, which experience has shown to be favorable for Paint adhesion and the corrosion protection of the phosphate layers produced with this effect. Accordingly, the phosphating solution according to the invention preferably additionally contains one or more of the following cations:

0.1 to 4 g / l manganese (ll),

0.2 to 2.5 g / l magnesium (ll),

0.2 to 2.5 g / l calcium (II),

0.002 to 0.2 g / l copper (II).

If desired, the phosphating solutions can contain about 0.2 to about 1.5 g / l of nickel ions. For health and ecological reasons, however, phosphating baths are preferred which have the lowest possible nickel ion content or, if desired, can also be nickel-free. For example, in a preferred embodiment, the phosphating solution according to the invention contains, in addition to zinc ions, 0.1 to 4 g / l of manganese ions and 0.002 to 0.2 g / l of copper ions as additional cations and not more than 0.05 g / l, in particular not more than 0.001 g / l nickel ions. However, if one wishes to adhere to the conventional trication technology, phosphating baths according to the invention can be used which, in addition to zinc ions, contain 0.1 to 4 g / l manganese ions and additionally 0.1 to 2.5 g / l nickel ions, but not more than 0.001 g / l contain copper ions.

The weight ratio of phosphate ions to zinc ions in the phosphating baths can vary within a wide range, provided it is in the range between 3.7 and 30. A weight ratio between 10 and 20 is particularly preferred. The skilled worker is familiar with the free acid and total acid contents as further parameters for controlling phosphating baths. Free acid values between 0 and 1.5 Points and the total acidity between about 15 and about 35 points are within the technical standard range and are suitable for the purposes of this invention.

Chlorate is preferably used as the sodium salt. Hydroxylamine can be used as a free base, as a hydroxylamine complex, as a hydroxylamine-releasing compound such as aldoxime or ketoxime or in the form of hydroxylammonium salts. If free hydroxylamine is added to the phosphating bath or a phosphating bath concentrate, it will largely exist as a hydroxylammonium cation due to the acidic nature of these solutions. When used as a hydroxylammonium salt, the sulfates, chlorides and phosphates are particularly suitable. In the case of the phosphates, the acid salts are preferred due to the better solubility. Hydroxylamine or its compounds are added to the phosphating bath in amounts such that the calculated concentration of the free hydroxylamine is preferably between 0.3 and 1.5 g / l.

When phosphating zinc-containing surfaces, it has proven to be advantageous to limit the nitrate content of the phosphating bath to a maximum of 0.5 g / l. This suppresses the problem of so-called speck formation and improves corrosion protection when using nickel-free phosphating baths. Phosphating baths which contain no nitrate are particularly preferred.

The zinc content of the phosphating bath will be set according to EP-A-315 059 to values between 0.45 and 1.1 g / l. As a result of the pickling removal during the phosphating of zinc-containing surfaces, it is possible that the current zinc content of the working bath is above a value of 1.1 g / l. Zinc levels up to 2 g / l are within the scope of the present Invention harmless. Depending on the system technology, zinc contents of up to 3 g / l can also reduce the risk of rust formation during phosphating. The form in which the cations are introduced into the phosphating baths is in principle irrelevant. It is particularly useful to use oxides and / or carbonates as the cation source.

In the case of phosphating baths which are said to be suitable for different substrates, it has become customary to add free and / or complex-bound fluoride in amounts of up to 2.5 g / l of total fluoride, of which up to 250 mg / 1 of free fluoride. The presence of such amounts of fluoride is also advantageous for the phosphating baths according to the invention. In the absence of fluoride, the aluminum content of the bath should not exceed 3 mg / 1. In the presence of fluoride, higher Al contents are tolerated as a result of the complex formation, provided the concentration of the non-complexed Al does not exceed 3 mg / 1.

In practice, it has been found that the hydroxylamine accelerator can be slowly inactivated even if no metal parts to be phosphated are introduced into the phosphating bath. It has surprisingly been found that the inactivation of the hydroxylamine can be significantly slowed down if one or more aliphatic hydroxycarboxylic acids with 3 to 6 carbon atoms in a total amount of 0.1 to 1.5 g / l are added to the phosphating bath. The hydroxycarboxylic acids are preferably selected from lactic acid, gluconic acid, tartronic acid, malic acid, tartaric acid and citric acid, citric acid being particularly preferred.

In principle, phosphating baths can be prepared directly on site by dissolving the individual components in the water in the desired concentration range. In practice, however, it is common to use concentrates to use, which contain the individual components in the desired proportions and from which the operational phosphating bath is prepared on site by dilution with water or which are added as a supplementary solution to a working phosphating bath in order to compensate for the consumption of the active components. However, such phosphating concentrates are strongly acidic for stabilization. After dilution with water, the pH and / or the free acid must therefore often be blunted to the desired range. For this purpose, alkaline substances such as sodium hydroxide solution or sodium carbonate or basic salts or hydroxides of Ca, Mg, Zn are added.

Accordingly, the invention also relates to an aqueous concentrate which, after dilution with water by a factor between 10 and 100 and, if necessary, adjustment of the pH to a working range between 2.5 and 3.6, a phosphating solution according to one or more of Claims 1 to 7 results.

Furthermore, the invention comprises a method for phosphating metal surfaces made of steel, galvanized or galvanized alloy steel and / or aluminum. As is becoming increasingly common in automotive engineering, the materials mentioned can also be present side by side. The metal surfaces are brought into contact with the phosphating solution according to the invention by spraying or dipping or by a combination thereof. The temperature of the phosphating solution is preferably in the range between about 40 and about 60 ° C.

The phosphating process can be used to phosphate steel or galvanized steel strips in conveyor systems. The phosphating times are in the range from about 3 to about 20 Seconds. However, the method can be used in particular in automobile construction, where treatment times between 1 and 8 minutes are common. It is intended in particular for the treatment of the metal surfaces mentioned before painting, in particular before cathodic electrocoating, as is customary in automobile construction. The phosphating process is to be seen as a sub-step of the technically usual pretreatment chain. In this chain, the steps of cleaning / degreasing, rinsing and activating are usually preceded by the phosphating, the activation usually being carried out using activating agents containing titanium phosphate. The phosphating according to the invention can, if appropriate after an intermediate rinse, be followed by a passivating aftertreatment. Treatment baths containing chromic acid are widely used for such a passivating aftertreatment. For reasons of work and environmental protection and for disposal reasons, however, there is a tendency to replace these chromium-containing passivation baths with chromium-free treatment baths. Purely inorganic baths, in particular based on zirconium compounds, or also organic baths, for example based on poly (vinylphenols), are known for this. When using phosphating solutions that contain neither nickel nor copper ions, a significant improvement in corrosion protection can be achieved if copper or silver ions are added to the baths for the passivating aftertreatment. For example, passivating rinse solutions can be used which contain 0.001 to 10 g / l copper ions and which, if desired, can be free of further passivating components. An intermediate rinse with deionized water is generally carried out between this post-passivation and the usually subsequent electrocoating. Embodiments

The phosphating processes and comparative processes according to the invention were checked on steel sheets (St 1405), as are used in automobile construction. The following process, common in body production, was carried out as a spray or immersion process:

1. Clean with an alkaline cleaner (Ridoline ^ 1559, Henkel KGaA), approach 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 ^ 50CF, Henkel KGaA), approach 0.1% in deionized water, room temperature, 1 minute.

4. Phosphating with phosphating baths and treatment parameters according to Table 1.

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 8.2.

5. Rinse with city water, room temperature, 1 minute.

6. Blow dry with compressed air The mass per unit area ("layer weight") was determined by dissolving in 5% chromic acid solution in accordance with DIN 50942.

Table 1: Bath parameters, layer weights

Bath parameters Comp. 1 Comp. 2 Ex. 1 Ex. 2 Ex. 3

Zn (g / l) 1, 3 1, 3 1, 3 1, 3 1, 3

Mn (g / l) 0.8 0.8 0.8 0.8 0.8

Ni (g / l) 0.8 - 0.8 0.8 -

Cu (g / l) - 0.01 - - 0.01

Phosphate (g / l) 15 15 15 15 15

Hydroxylamine sul- 2.0 2.0 2.0 2.0 2.0 fat (g / l)

Chlorate (g / l) - - 2.0 3.0 2.0

Free acid 1, 1 1, 1 1, 1 1, 1 1.1

(Points)

(pH = 3.6)

Total acidity 26 25 26 26 25

(Points)

Dive time (s) 180 180 180 180 180

Temperature (° C) 53 53 53 53 53

Layer weight 3.0 3.5 2.7 2.3 3.0

(g / m ² ) normal bath movement

Layer image iOiOiOiOiO Continuation of table 1

Bath parameters Comp. 1 Comp. 2 Ex. 1 Ex. 2 Ex. 3

Layer weight n.g. n.g. 3.3 3.0 3.6

(g / m ² ) no bath movement such as in cavities

Layered image rust rust ok OK OK

OK = ok n.s. = not measured

To test the stability of hydroxylamine against chlorate, a sufficient amount of additional hydroxylamine sulfate was added to a phosphating bath according to Comparative Example 1 so that the analytical content of hydroxylamine sulfate was 2.7 g / l. This phosphating bath was mixed with 2.0 g / l chlorate ions in the form of sodium chlorate. The phosphating bath was then stirred at 50 ° C. for 16 hours. The analytically determinable hydroxylamine sulfate content was 2.6 g / l. The hydroxylamine content was determined analytically by the acetone / bromate method customary in the prior art.

Claims

claims

1. Containing acidic, aqueous phosphating solution

0.2 to 3 g / l zinc ions

3 to 50 g / l phosphate ions, calculated as PO ₄ ^{3 "} and accelerator,

characterized in that the solution as an accelerator

2. Phosphating solution according to claim 1, characterized in that it additionally contains one or more of the following cations:

0.1 to 4 g / l manganese (ll),

0.2 to 2.5 g / l magnesium (ll),

0.2 to 2.5 g / l calcium (ll),

0.002 to 0.2 g / l copper (II).

3. Phosphating solution according to claim 2, characterized in that it contains 0.1 to 4 g / l manganese ions and 0.002 to 0.2 g / l copper ions and not more than 0.05 g / l nickel ions.

4. phosphating solution according to claim 3, characterized in that it contains not more than 0.001 g / l of nickel ions.

5. phosphating solution according to claim 2, characterized in that it contains 0.1 to 4 g / l manganese ions and not more than 0.001 g / l copper ions and additionally 0.1 to 2.5 g / l nickel ions.

6. phosphating solution according to one or more of claims 1 to 5, characterized in that it contains no more than 0.5 g / l nitrate ions.

7. phosphating solution according to one or more of claims 1 to 6, characterized in that it additionally contains free and / or complex fluoride in amounts of up to 2.5 g / l total fluoride, of which up to 250 mg / l free fluoride, each calculated as F ^" .

8. Aqueous concentrate, which after dilution with water by a factor between 10 and 100 and optionally adjusting the pH to a working range between 2.5 and 3.6 results in a phosphating solution according to one or more of claims 1 to 7.

9. A method for phosphating metal surfaces made of steel, galvanized or alloy galvanized steel and / or aluminum, in which the metal surfaces are sprayed or dipped or by a combination thereof for a time between 3 seconds and 8 minutes with a phosphating solution according to one or more of claims 1 to 7 in contact.