WO1990010094A1

WO1990010094A1 - Process for producing zinc/barium phosphate coatings on metal surfaces

Info

Publication number: WO1990010094A1
Application number: PCT/EP1990/000287
Authority: WO
Inventors: Reinhard Seidel; Karl-Dieter Brands
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1989-03-03
Filing date: 1990-02-21
Publication date: 1990-09-07
Also published as: EP0385251A1; PT93307A; EP0461133A1; AU5109490A; DE3906898A1; DE59004443D1; EP0461133B1; KR920700308A

Abstract

The invention concerns a process for producing phosphate coatings on the surfaces of metals, in particular iron, steel, zinc, zinc/nickel alloys, aluminium and/or its alloys or aluminium-steel composites, by spraying, spray dipping and/or dipping, with an aqueous solution containing: 0.01 to 5 g/l of zinc(II) ions, 0.3 to 10 g/l of barium(II) ions, 3 to 50 g/l of phosphate ions, 0 to 2 g/l of fluoride ions, and as accelerator: 0.5 to 30 g/l of nitrate ions and/or 0.01 to 1 g/l of nitrite ions and/or 0.2 to 10 g/l of chlorate ions and/or 0.1 to 2 g/l of an organic nitro compound and/or 0.01 to 5 g/l of a peroxide compound, the pH value of the solution being adjusted to between 2 and 4.

Description

Zinc-Bariu-Phosphating of metal surfaces

The invention relates to a method for producing phosphate coatings on metal surfaces, in particular surfaces made of iron, steel, zinc, zinc / nickel alloys and / or aluminum and their alloys by means of an acidic aqueous solution containing zinc (II) ions, Barium (II) ions, phosphate ions and accelerators and, if appropriate, other additives, and the use of this process to prepare the surfaces for subsequent painting, in particular cathodic electrocoating.

The protection of metallic surfaces by phosphate-containing coatings has been known for a long time, cf. for example the monograph of. Rausch, "The Phosphating of Metals", Leuze Verlag, Saulgau (1988). Thus, in the "non-layer-forming phosphating" process, the use of alkali and / or ammonium orthophosphate solutions produces iron phosphate layers in which the iron ion comes from the metallic surface to be coated. In so-called "layer-forming phosphating", treatment with acidic phosphating solutions, which typically contain phosphoric acid, oxidizing compounds and divalent layer-forming ions such as zinc alone or together with calcium, manganese, iron, cobalt, nickel and other metal ions, results in amorphous or crystalline phosphate layers on metal surfaces generated. In most cases, phosphophyllite Zn2Fe (PO_ι) 2 is formed as crystalline phosphate phases. H2θ and / or Hopeit Zn3 (Pθ4) 2-4H2θ or isostructural phases doped with other divalent metal ions and, in the presence of calcium, also scholzite Zn2Ca (Pθ4) 2-2H2θ (WA Roland, K.-H. Gottwald, "Metall¬ surface" , 42nd year 1988/6, pp. 301 to 305). It is known that the above-mentioned tetrahydrates dehydrate under the baking conditions of paints (typically 180 ° C. for cathodic electrocoating) with elimination of water and formation of the corresponding dihydrates (Y. Arnaud et al., Appl. Surf. Sci. 32, 281-308 (1988)). This release of water is accompanied by a breakdown of the crystalline structure of the individual phosphate crystals. This leads to a reduction in the cohesion within the phosphate layer, which in turn has a negative effect on the adhesion between the lacquer and the substrate.

It is also known that very high pH values of 12 to 13 are achieved in the case of corrosion beneath destroyed paint coatings (paint rusting). Conventional zinc phosphate coatings are soluble under these conditions, which leads to the lacquer becoming detached from the substrate.

Phosphates with the general formula BaZn2-. _nn (P04) 2 mt M = Co2 ⁺ , Mg ²⁺ and 0.0 ≤ n 0.8 are claimed in DE-0S 24 47 208 as corrosion protection pigments.

In contrast, the object of the present invention was to provide a method for producing phosphate coatings on metal surfaces, wherein conversion layers are produced which have a particularly high alkali resistance and are exposed to thermal stresses due to the baking temperatures typically used for cathodic electrocoating and higher temperatures are not subject to changes.

Surprisingly, it was found that the use of acidic aqueous phosphating solutions which essentially contain barium (II), zinc (II) and phosphate ions can produce conversion layers on metal surfaces which have a high level Have alkali resistance and are not subject to changes under thermal loads of up to around 300 ° C.

The present invention thus relates to a method for producing phosphate coatings on surfaces of iron, steel, zinc, galvanized steel, nickel, aluminum and / or their alloys or aluminum-steel composites by spraying, splash-dipping and / or dipping with an aqueous Solution containing: 0.01 to 5 g / 1 zinc (II) ions, 0.3 to 10 g / 1 barium (II) ions, 3 to 50 g / 1 phosphate ions, 0 to 2 g / 1 fluoride -Ions and as accelerators: 0.5 to 30 g / 1 nitrate ions and / or 0.01 to 1 g / 1 nitrite ions and / or 0.2 to 10 g / 1 chlorate ions and / or 0, 1 to 2 g / 1 of an organic nitro compound and / or 0.01 to 5 g / 1 of a peroxo compound, the pH of the solution being adjusted between 2 and 4.

It was found that, in contrast to known phosphating processes, the only or main constituent of these layers is a barium dizinc phosphate. The X-ray powder diagrams of the coatings are identical to those of "BaZn2 (PO4) 2" (MV Hoffman, J. Electrochem. Soc. 110, 1223 to 1227 (1963)). According to its own thermoanalytical investigations, however, there is a monohydrate which releases its water of crystallization at about 300 ° C. In barium dizinc phosphate, up to 40 mol% of zinc can be replaced by Co2 ⁺ or Mg2 ⁺ diadoch. All compounds are very difficult to dissolve in alkaline media. According to a first preferred embodiment of the process according to the invention, aqueous solutions are used which contain 0.5 to 1.5 g / 1 zinc (II) ions, 0.3 to 1.5 g / 1 barium (II) ions,

3 to 15 g / 1 phosphate ions,

0 to 1 g / 1 fluoride ions and as accelerator:

1 to 10 g / 1 nitrate ions and / or 0.01 to 1 g / 1 nitrite ions and / or 0.2 to 10 g / 1 chlorate ions and / or

0.1 to 2 g / 1 of an organic nitro compound and / or

Contain 0.01 to 5 g / 1 of a peroxo compound, the pH of the solutions being in the range from 2 to 3.

In the sense of this first embodiment of the method according to the invention, it is particularly preferred to use aqueous solutions which:

0.5 to 1.1 g / 1 zinc (II) ions, 0.5 to 1.1 g / 1 barium (II) ions,

4 to 10 g / 1 phosphate ions, 0.5 to 1 g / 1 fluoride ions and as accelerators:

Contain 2 to 4 g / 1 nitrate ions and 0.1 to 1 g / 1 nitrite ions.

In carrying out the process according to the invention in the sense of vor¬-defined first embodiment, it is further preferred that the amounts of substance of barium (II) - _f zinc (II) - and phosphate ions in a weight chtsVerhältnis 1: 2: (9 to 12) , in particular in a weight ratio of 1: 2: 10. According to a second preferred embodiment of the process according to the invention, aqueous solutions are used which

0.1 to 2.5 g / 1 zinc (II) ions, 1 to 7 g / 1 barium (II) ions, 10 to 30 g / 1 phosphate ions,

0 to 1 g / 1 fluoride ions and as accelerator:

1 to 10 g / 1 nitrate ions and / or 0.1 to 1 g / 1 nitrite ions and / or 0.5 to 5 g / 1 chlorate ions and / or

Contain 0.1 to 2 g / 1 of an organic nitro compound, the pH of the solutions being in the range from 2.5 to 3.8.

In the sense of this second embodiment of the process according to the invention, it is furthermore particularly preferred to use aqueous solutions which contain 0.1 to 1 g / 1 zinc (II) ions,

2 to 6 g / 1 barium (II) ions, 10 to 30 g / 1 phosphate ions,

0.5 to 1 g / 1 fluoride ions and as accelerator:

1 to 5 g / 1 nitrate ions and / or

0.1 to 1 g / 1 nitrite ions and / or

0.5 to 5 g / 1 chlorate ions and / or

Contain 0.1 to 2 g / 1 of an organic nitro compound.

When carrying out the method according to the invention in the sense of the second embodiment defined above, it is also adds that the amounts of zinc (II), barium (II) and phosphate ions in a weight ratio of 1: (1 to 30): (7 to 200), in particular in a weight ratio of 1: (2 to 20) : (15 to 90) can be set.

The treatment temperature is, depending on the type of application, between 40 and 80 ° C. Depending on the type of application, the treatment times are between 1 and 10 minutes. In this way, crystalline, dense and homogeneous coatings with layer weights of approximately 0.5 to approximately 10 g / m2 are produced.

The aluminum materials to be treated by the method according to the invention include the pure metal and its alloys. Pure aluminum, AlMg, AlCu and AlMgSi alloys are therefore mentioned as examples. A detailed description of these materials can be found, for example, in the "Aluminum Pocket Book", 14th edition, Aluminum-Verlag, Düsseldorf, 1983. The steels (CRS) to be treated with the aid of the method according to the invention are, in particular, consumer goods such as automobile bodies, automobile accessories and spare parts, agricultural equipment, refrigerators and other types of small parts which are usually used in the form of sheet metal. The term "galvanized steel" includes galvanizing by electrodeposition (ZE) and hot dip application (Z) and thus refers to zinc and known zinc alloys, in particular zinc / nickel alloys.

To carry out the process according to the invention, the aqueous phosphating solutions can be applied to the substrate surfaces both by spraying, by immersion and by spray-immersion. When carrying out the process according to the invention in the spraying process, the spraying time must be selected in such a way that that a largely closed phosphate layer is formed. Modern full immersion systems are characterized by a large number of steps connected in series. The term "full immersion system" results from the phosphating by immersion application. In other process steps, spraying processes are also carried out, with spraying out of the immersion bath after the body has appeared.

A separate activation step may be important for optimal phosphating. For pre-cleaning and activation of the layer to be phosphated, it is usually cleaned, rinsed and then activated before phosphating in several work steps. For example, aqueous suspensions containing titanium phosphate according to the prior art can be used here. If necessary, the phosphate layers obtained can also be aftertreated in a manner known per se, i.e. passivated.

Compliance with the concentration ranges of the aqueous phosphating baths according to the invention is an essential component for the production of high quality, i.e. uniform phosphate coatings. If the concentrations are undershot, the layers become uneven. In particular, their suitability for subsequent electrodeposition painting decreases.

As stated above, a certain proportion of the zinc can be replaced by cobalt and / or magnesium in the barium-dizinc phosphates obtained according to the invention. Accordingly, a further preferred embodiment of the present invention is that aqueous solutions are used which additionally contain 0.01 to 0.6 g / l of cobalt (II) ions. A further preferred embodiment of the present invention consists in using aqueous solutions which additionally contain 0.01 to 0.3 g / 1 magnesium (IΙ) ions included. Diadoch replacement of zinc ions also enables the simultaneous use of cobalt (II) ions and magnesium (II) ions.

The aqueous solutions used for the process according to the invention can furthermore also contain 0.01 to 0.5 g / 1 iron (III) ions.

The phosphating layers produced when the process according to the invention is carried out prove to be very resistant to attack by alkalis, i.e. in a strongly alkaline environment, as well as against thermal loads. Another advantage of the process according to the invention is that the sludge formation in the phosphating bath is extremely low, especially if the preferred procedures are followed.

The method according to the invention can advantageously be used for the pretreatment of metal surfaces before subsequent painting; it is used in particular for the pretreatment of metal surfaces before cathodic electrocoating.

The phosphating baths for carrying out the process according to the invention are generally prepared in the customary manner which is known per se to the person skilled in the art. The starting materials for the production of the phosphating bath can be, for example, the oxides, nitrates or carbonates of the required metal cations, for example barium carbonate or nitrate and zinc nitrate or oxide. Cobalt and magnesium are preferably used in the form of cobalt nitrate and magnesium oxide, iron in the form of iron nitrate. The nitrate required is preferably introduced as a zinc and / or barium salt, as mentioned above, if appropriate also in Form of the sodium salt. The required amounts of nitrite, chlorate and fluoride ions are also added to the bath in the form of the sodium salts; the fluoride ions optionally also in the form of fluorosilicic acid and / or fluoroboric acid. According to the invention, the sodium salt of 3-nitrobenzenesulfonic acid is used as the preferred organic nitro compound, and hydrogen peroxide is used as the preferred peroxo compound. Phosphoric acid serves as the source of the phosphate ions. The pH of the bath is adjusted to the desired value by adding aqueous sodium hydroxide solution.

Examples

The process is carried out in the usual process sequence (see Table 1) with the stages: mechanical and chemical cleaning and degreasing, rinsing, pickling, rinsing, optionally activating, phosphating, VE rinsing.

T a b e 11 e 1

Treatment steps as part of the standard phosphating process

Stage treatment treatment concentration temperature treatment step with (% by weight) <° C) time (min)

1 ιne-Han absorbent

Cleaning and paper - 20 5

Degrease

2 chemical Ridoline ¹ *

Clean and C 1250E ¹ ) 5 55 2

Degrease

Rinse tap water 2) 20

continuation

Continuation of table 1

Stage treatment treatment concentration temperature treatment step with (% by weight) (° C) time (min)

4 Phosphating • see table 1 1 e 2

5 Rinsing deionized water 3) - 20 1

6 Drying compressed air - 20 to dryness

1) Commercial alkaline _/ phosphate-containing sprite / immersion cleaner from Collardin, Cologne

2) untreated city water with 18 ° d

3) demineralized water

Table 2

Example 1 2 3 4 5 6 7 8 9 10

Substrate: CRS X X X X X

Z X

ZE X X X X phosphating solution:

Zn ²⁺ (g / 1) 0.3 0.1 0.3 0.6 0.4 0.6 0.1 0.6 0.6 1.0

Ba ²⁺ "2.5 2.5 2.5 5.0 2.5 5.0 2.5 2.0 0.6 1.0

PO4 ³ - "17 17 17. 17 17 17 17 17 5 9

NO3- "3.0 3.0 3.4 3.4 3.2 3.2 3.0 3.2 3.4 3.4 rv>

N0 ₂ "" 0.2 0.2 - 0.2 0.1 0.2 0.2 0.2 0.2 0.2

CIO3- "1.0 - Ifetriium nitrobenzene sulfonate" - - 0.6 - - - - - -

F ~ "0.8 0.8 0.8 0.6 0.6 0.6 0.8 0.6 0.8 0.8 g2 +« _ _ _ _ _ _ o, 2 -

Co ²⁺ "_ _ _ _ _ _ _ o, 4 - -

pH "3.5 3.0 3.2 3.3 3.3 3.0 3.4 3.2 2.8 2.5

continuation

Continuation of table 2

Example 1 2 3 4 5 6 7 8 9 10

Temperature (° C) 60 60 60 60 60 60 60 60 60 75

Treatment time (πiin) 1 2 2 2 3 3 1 2 3 5

Process S T T S T T S S S T

(Spraying / dipping) appearance of the phosphate fine crystalline and closed

Layer ^w

Layer weight (g / m ² ) 2.6 2.9 2.6 0.9 1.9 1.6 2.1 1.7 1.1 0.7

ScMcM decrease after 1 hour in 17 15 15 11 13 11 14 12 16 9

After 0.1N in% uriteccwareierung

480 h salt spray test 0.3 0.3 0.2 0.1 0.1 0.1 0.2 0.1 0.2 0.1 in mm

Steel sheets (CRS), electrolytically galvanized steel sheets (ZE) and hot-dip galvanized steel sheets (Z), which had previously been cleaned with an alkaline cleaner for 2 minutes at 55 ° C. by spray treatment and rinsed with water, were used with the aforementioned treated phosphating solutions (Table 2). It was then rinsed with deionized water and dried.

The phosphate layers produced were finely crystalline and closed; they consisted exclusively of barium dizinc phosphate.

In addition, phosphated sheets were coated with a cathodic electro-dip coating (Aqualux ^R K from ICI, Germany, based on epoxy resin) and dried at 180 ° C. for 20 minutes. The dry film thickness was 20 μm. The Ba / Zn phosphate layer was not changed in this treatment. The sheets were then provided with a single cut in accordance with DIN 53 167 and subjected to the salt spray test in accordance with DIN 50 021 for a period of 480 h. The evaluation was carried out according to DIN 53 167.

The results obtained are also shown in Table 2.

Claims

Patent claims

1. Process for producing phosphate coatings on metal surfaces, in particular surfaces made of iron, steel, zinc, zinc / nickel alloys, aluminum and / or their alloys or aluminum-steel composites by spraying, splash-dipping and / or dipping with a aqueous solution containing:

0.01 to 5 g / 1 zinc (II) ions,

0.3 to 10 g / 1 barium (II) ions,

3 to 50 g / 1 phosphate ions,

0 to 2 g / 1 fluoride ions and as accelerator:

0.5 to 30 g / 1 nitrate ions and / or

0.01 to 1 g / 1 nitrite ions and / or

0.2 to 10 g / 1 chlorate ions and / or

0.1 to 2 g / 1 of an organic nitro compound and / or

0.01 to 5 g / 1 of a peroxo compound, the pH of the solution being adjusted between 2 and 4.

2. The method according to claim 1, characterized in that one uses an aqueous solution, the

0.5 to 1.5 g / 1 zinc (II) ions,

0.3 to 1.5 g / 1 barium (II) ions,

3 to 15 g / 1 phosphate ions,

0 to 1 g / 1 fluoride ions and as accelerator:

1.0 to 10 g / 1 nitrate ions and / or

0.01 to 1 g / 1 nitrite ions and / or

0.2 to 10 g / 1 chlorate ions and / or 0.1 to 2 g / 1 of an organic nitro compound and / or

Contains 0.01 to 5 g / 1 of a peroxo compound, the pH of the solution being adjusted between 2 and 3.

3. .Verfahren according to claim 2, characterized in that one uses an aqueous solution, the

0.5 to 1.1 g / 1 zinc (II) ions,

0.5 to 1.1 g / 1 barium (II) ions,

4 to 10 g / 1 phosphate ions,

0.5 to 1 g / 1 fluoride ions and as accelerator:

2 to 4 g / 1 nitrate ions and

Contains 0.1 to 1 g / 1 nitrite ions.

4. The method according to claim 2 or 3, characterized in that the amounts of the barium (II), zinc (II) - and phosphate ions in a weight ratio of 1: 2: (9 to 12), preferably 1: 2 : 10, can be set.

5. The method according to claim 1, characterized in that one uses an aqueous solution, the

0 to 1 g / 1 fluoride ions and as accelerator:

1 to 10 g / 1 nitrate ions and / or 0.1 to 1 g / 1 nitrite ions and / or 0.5 to 5 g / 1 chlorate ions and / or Contains 0.1 to 2 g / 1 of an organic nitro compound, the pH of the solution being set between 2.5 and 3.8.

6. The method according to claim 5, characterized in that one uses an aqueous solution, the

0.1 to 1 g / 1 zinc (II) ions,

2 to 6 g / 1 barium (II) ions,

10 to 30 g / 1 phosphate ions,

0.5 to 1 g / 1 fluoride ions and as accelerator:

1 to 5 g / 1 nitrate ions and / or

0.1 to 1 g / 1 nitrite ions and / or

0.5 to 5 g / 1 chlorate ions and / or

Contains 0.1 to 2 g / 1 of an organic nitro compound.

7. The method according to claim 5 or 6, characterized in that the amounts of zinc (II), barium (II) and phosphate ions in a weight ratio of 1: (1 to 30): (7 to 200), preferably

1: (2 to 20): (15 to 90).

8. The method according to any one of claims 1 to 7, characterized gekenn¬ characterized in that aqueous solutions are used which contain 0.01 to 0.6 g / 1 cobalt (II) ions.

9. The method according to any one of claims 1 to 7, characterized gekenn¬ characterized in that aqueous solutions are used which contain 0.01 to 0.3 g / 1 magnesium (II) ions.

10. The method according to any one of claims 1 to 7, characterized gekenn¬ characterized in that aqueous solutions are used which contain 0.01 to 0.5 g / 1 iron (III) ions.

11. The method according to any one of claims 1 to 10, characterized gekenn¬ characterized in that barium-dizinc-phosphate coatings are produced.

12. Application of the method according to one of claims 1 to 11 for the preparation of the metal surfaces for the cathodic electro-dip coating.