WO2001059180A1

WO2001059180A1 - Method for coating metal surfaces, aqueous concentrate used therefor and use of coated metal parts

Info

Publication number: WO2001059180A1
Application number: PCT/EP2001/000627
Authority: WO
Inventors: Detlev Seifert
Original assignee: Chemetall Gmbh
Priority date: 2000-02-12
Filing date: 2001-01-20
Publication date: 2001-08-16
Also published as: DE10006338A1; DE10006338C2; AU2001228477A1

Abstract

The invention concerns a method for coating metal surfaces with a pre-treatment layer before depositing a thin electrophoretic enameling layer. The method is characterized in that a pre-treatment layer is deposited, which is based on iron phosphate/iron oxide/iron hydroxide with a copper, silver, gold, platinum, iridium, osmium, palladium, rhodium and/or ruthenium content. The invention also relates to an aqueous concentrate for the preparation of an aqueous solution for depositing the pre-treatment layer, having the following content: 0.005 to 0.4 percent by weight of ions of copper, silver, gold, platinum, iridium, osmium, palladium, rhodium and/or ruthenium; 5 to 30 percent by weight P2O5 of phosphate ions; 0.2 to 5 percent by weight of at least one accelerator; molybdenum ions and/or molybdate ions totaling 0.1 to 1 percent by weight, calculated as MoO3, and 0.1 to 2 percent by weight of free fluoride ions.

Description

Process for coating metal surfaces, aqueous concentrate therefor and use of the coated metal parts

The invention relates to a method for coating metal surfaces with a pretreatment layer prior to the deposition of a thin electrocoat layer, an aqueous concentrate for preparing the aqueous solution for the deposition of the pretreatment layer and the use of the products produced by the method according to the invention.

Processes for producing iron phosphate coatings as pretreatment layers before painting are fundamentally well known. Coatings of this type are also referred to as alkali phosphate coatings or according to Werner Rausch: The phosphating of metals, Saulgau 1988, as layers of the so-called “non-layer-forming phosphating”, this designation being misleading, since layers are also formed here, but are significantly thinner The layers of iron phosphating are, in contrast to the crystalline layers of the other types of phosphating, X-ray amorphous. In addition, the layers of iron phosphating are largely or completely free of manganese and zinc. The pH of the Phosphate baths are usually in the range from 2.5 to 3.5 in the case of the aqueous solutions forming crystalline layers, and those in the iron phosphating are usually in a range above 3.4.

In general, iron phosphate coatings are produced as pretreatment layers before painting by contact with an acidic aqueous mono- or / and orthophosphate-containing phosphating solution and then by electrocoating the entire metal surface and often also by subsequent powder painting of the surface parts that are easily accessible from the outside. These processes are being pushed to the max today. The aim is to make these processes more reliable and cost-effective. The comparatively thick electrocoat layer, which is common today in the case of undercuts or / and with a complicated structure, is a major cost component concealed metal parts such as. B. some radiator elements is still at least 12 μm, often more than 15 μm, as the average over the entire surface. Because of the undercuts or hidden cavities, it is often necessary to use approx. 250 V instead of approx. 40 V for electro-dipping, in order to enable a closed coating application even in the poorly accessible areas (Faraday cage). In this case, an unnecessarily thick electrodeposition coating is applied to the easily accessible and therefore easily paintable areas of the metal parts. In this case, it would be sufficient if a continuous, namely a so-called layered, electrocoating layer were achieved. Reducing the thickness of the electrocoat layer by just 1 μm on average can already result in six-figure DM savings per year in paint shops.

Surprisingly, it was found that the addition of ions of copper and chemically related metals to the phosphating solution allows a pretreatment layer to be formed on which the deposition of the electrodeposition paint is accelerated and made more uniform. In the area of the undercuts or hidden cavities, the varnish deposition in the method according to the invention is significantly better compared to the easily accessible parts than in the method according to the prior art.

The object of the invention is to propose an iron phosphating process in which it is possible to apply the subsequently applied electrocoat layer as a whole thinner than according to the prior art, without thereby impairing the corrosion protection.

The object is achieved by a method for coating metal surfaces with a pretreatment layer prior to the deposition of a thin electrocoat layer, in which a pretreatment layer based on iron phosphate / iron oxide / iron hydroxide containing copper, silver, gold, platinum, iridium, osmium, palladium, Rhodium or / and ruthenium is deposited. Claims 2 to 18 further develop the method. Furthermore, the object is achieved by an aqueous concentrate according to claim 19.

In the method according to the invention, an aqueous solution (phosphating solution) is preferably used for the deposition of the pretreatment layer, which contains ions of copper, silver, gold, platinum, iridium, osmium, palladium, rhodium and / or ruthenium in the range of 0.2 has up to 40 mg per liter, in particular from 0.5 to 20 mg per liter, preferably from 1 to 15 mg per liter, particularly preferably from 2 to 10 mg per liter. Copper ions are preferred, as are mixtures of copper ions with ions of one of the other noble metals mentioned.

The effect of the ions of copper or the other noble metals mentioned has not yet been fully understood. Local elements may thereby form on the surface, which reduce the electrical resistance and accelerate the process of electrodeposition coating. This addition also provides even higher temporary corrosion protection.

The phosphate solution in the phosphate solution can be in the range from 1 to 10 g per liter, preferably from 2 to 8 g per liter, particularly preferably from 3.5 to 5.5 g per liter. The phosphate, in particular to a concentrate, is preferably added by adding orthophosphoric acid.

The phosphating solution preferably has an ion content of at least one alkali metal and / or alkaline earth metal, in particular sodium, in the range from 0.3 to 3.5 g per liter, preferably from 0.6 to 3 g per liter, particularly preferably from 1 to 2.5 g per liter. The addition of sodium ions helps to adjust the pH and is preferably bound to the phosphoric acid. The sodium ions can be introduced, for example, by adding sodium hydroxide. The phosphating solution preferably has an ammonium ion content in the range from 2 to 50 mg per liter, preferably from 5 to 30 mg per liter, particularly preferably from 8 to 20 mg per liter. The ammonium ions in combination with molybdate / molybdenum ions can cause the oxidation of Fe ° or Fe ²⁺ to Fe ³⁺ or corresponding other metals or metal ions. They therefore have an accelerating effect.

The phosphating solution preferably has a free fluoride ion content in the range from 0 to 400 mg per liter, preferably from 1 to 350 mg per liter, particularly preferably from 50 to 300 mg per liter. Fluoride is preferably added by adding hydrofluoric acid.

The phosphating solution preferably has a content of molybdenum ions and / or molybdate ions in the range from 0 to 500 mg per liter, in particular at least 5 mg per liter, preferably from 15 to 250 mg per liter, particularly preferably from 30 to 200 mg per liter as MoO ₃ .

The phosphating solution preferably has a nitrate ion content in the range from 0 to 5 g per liter, preferably from 0.001 to 2 g per liter, particularly preferably from 0.002 to 1 g per liter. The content of nitrate ions enables the pickling attack to be increased, the phosphate layer formation to be evened out and has an accelerating effect.

The phosphating solution preferably has a content of at least one nonionic and / or anionogenic surfactant in the range from 50 to 5000 mg per liter, preferably from 100 to 4000 mg per liter, particularly preferably from 200 to 3000 mg per liter. These surfactants ensure better wetting of the metal surface and thus more uniform removal of organic contaminants on the metal surface, more uniform pickling attack on the metal surface and more uniform formation of phosphate layers on the metal surface. The phosphating solution preferably has a content of at least one organic solubilizer in the range from 0 to 200 mg per liter, preferably from 10 to 100 mg per liter, particularly preferably from 20 to 80 mg per liter. The solubilizers serve to ensure that the surfactants remain in one component in the aqueous solution.

The phosphating solution preferably has a content of at least one accelerator, in particular an accelerator selected from the group of nitroguanidine, chlorate ions and NBS ions, in the range from 0 to 3 g per liter, preferably from 0.2 to 2.5 g per liter, particularly preferably from 0.3 to 2 g per liter. This accelerator works in a wider pH range, so that you can work in a wider pH range.

For reasons of environmental protection, the phosphating solution advantageously has no or only a low content of nitrite ions, chromium ions, nickel ions, cobalt ions, manganese ions, cadmium ions and zinc ions. Significant levels of these ions usually only occur when such ions are released from the metallic surface. If the bath had a higher content of at least one of these substances, the processed solution might have to elaborate disposal can be arranged.

Furthermore, the phosphating solution preferably also contains no chloride and sulfate ions for reasons of corrosion protection of the metal parts to be coated.

Certain levels of aluminum in the phosphating solution may possibly for the precipitation of cryolite, such as calcium lead to the precipitation of calcium fluoride. It is therefore advantageous to keep the contents of such ions within limits in which precipitation can be avoided or kept to a minimum.

The phosphating solution preferably has a temperature in the range from 30 to 70 ° C., preferably from 40 to 65 ° C., particularly preferably from 50 to 60 ° C. The phosphating solution preferably has a pH in the range from 3.5 to 6.5, preferably from 4 to 5.5, particularly preferably from 4.5 to 4.8. The pH should be set comparatively precisely.

The phosphating solution preferably has a total acid number in the range from 2 to 20, preferably from 6 to 14, very particularly preferably from 8 to 12.

The total acid score is the number of ml that results when 10 ml of phosphating solution, which has been diluted to 50 ml with deionized water, is titrated with 0.1 normal sodium hydroxide solution to a pH of 8.7.

The phosphating solution preferably has a free acid content of up to 2 points, preferably from 0 to 1.5 points, particularly preferably from 0.01 to 1 point.

The free acid score is the number of ml that results when 10 ml of phosphating solution, which has been diluted to 50 ml with deionized water, is titrated with 0.1-normal sodium hydroxide solution to a pH of 4.2. whereby KCI is added to the sample to be titrated to saturation if the sample contains complex-bound fluoride in order to largely prevent its dissociation.

As water quality for the phosphating solution, as well as for the aqueous concentrate, which can be used both for making up and for supplementing the phosphating solution, are city water, which is preferably decarbonized at higher degrees of hardness, but also purer water qualities, e.g. demineralized water well suited.

Depending on whether the pretreatment is carried out in a 2, 3 or 4 zone system, the treatment course can include the following steps: a) Cleaning and phosphating with the phosphating solution according to the invention

- Rinse with water

b) cleaning and phosphating with the phosphating solution according to the invention

- Rinsing with water - Rinsing with water

c) Pre-cleaning with a first phosphating solution according to the invention

- Cleaning and phosphating with a second phosphating solution according to the invention - rinsing with water - rinsing with water.

For the step of cleaning and phosphating, preferably with a spraying time of 0.5 to 4 minutes, in particular over 0.8 to 3 minutes, very particularly over 1 to 2 minutes with a spray pressure in the range from 0.3 to 2.5 bar worked. Alternatively, the metal parts can also be immersed in a bath for a period of 1 to 10 minutes, particularly 1.5 to 6 minutes. In the case of a process with a 4-zone system, the times mentioned refer to the sum of the pretreatment times for pre-cleaning / phosphating and cleaning / phosphating.

As with c), cleaning and phosphating can also be carried out in two successive baths: It is advisable to set a higher total acid number in the first bath than in the second bath and to ensure that the free acid content in both baths is as low as possible is.

The rinsing is preferably carried out over a period of 20 to 80 seconds with a spray pressure of 0.3 to 2.5 bar. An unheated bath with fresh water supply of city water quality is sufficient. City water quality is preferred in order to have a larger buffer effect.

The rinsing can be carried out for 20 to 80 seconds with a spray pressure of 0.3 to 2.5 bar. Deionized water is preferably used here. The salt load should be reduced as much as possible by suitable measures such as downstream spray ring with deionized water. After the last spraying step, the drained water should not exceed an electrical conductivity value of 50 μS / cm due to the subsequent electrodeposition.

The metal parts pretreated in this way are usually moved directly into the electrocoating system. Drying can then be omitted.

The method according to the invention is preferably used for metal parts - in particular for those of complex geometry - particularly preferably for metal parts made of iron or steel materials, aluminum or aluminum alloys, magnesium alloys or galvanized metal parts. The method according to the invention can be used in particular for simple structural steels such as e.g. Use St 370 well.

The pretreatment layer can be referred to as a conversion layer, even though ions which have been removed from the metal surface are involved in the layer structure. It is ideal as temporary storage protection and as a primer for paintwork. The pretreatment layer preferably has a thickness of 0.05 to 0.6 μm, in particular 0.15 to 0.4 μm, and a weight per unit area of 0.1 to 1.2 g / m ² , preferably 0.2 to 0 , 8 g / m ² . It is advantageously amorphous.

The pretreatment layer has contents of iron phosphate, iron oxide and / or iron hydroxide. It is the result of a so-called iron phosphating.

Lacquer layers with a layer thickness of 0.5 to 100 μm can be applied to the pretreatment layer, in particular by cathodic or anodic dip coating and, if appropriate, by at least one subsequent coating. According to the state of the art, the first dip coating layer applied to the pretreatment layer has a layer weight in the range from 18 to 22.5 g / m ² , which, assuming a density of the baked coating layer of 1.5 g / cm ^{3, has} an average layer thickness in the range from 12 to 15 μm, or even higher Layer weights, while in the method according to the invention on similar metal parts with hidden areas, a layer weight approximately in the range of 12 to 17.5 g / m ² , which assuming a density of the baked lacquer layer of 1.5 g / cm ^{3 of} an average layer thickness in Range of 8 to 11.7 microns corresponds.

In addition to such an immersion lacquer layer, a lacquer layer or a different organic coating or / and an adhesive layer, in particular with lacquered metal parts such as e.g. be applied in the form of plates. The additional lacquer layer usually has decorative functions and slightly improves corrosion protection; it is often applied by powder painting.

With an adhesive layer, which is preferably applied to the additional lacquer layer, metal or plastic parts can be glued on, which are advantageously also pretreated and / or painted. These glued parts have e.g. in the case of flat radiators, often the shape of plates.

According to the invention, an aqueous concentrate which has the following contents is used to prepare the phosphating solution:

Ions of copper, silver, gold, platinum, iridium, osmium, palladium, rhodium and / or ruthenium in each case from 0.005 to 0.4% by weight, preferably from 0.01 to 0.2% by weight, particularly preferably from 0.02 to 0.15% by weight, in particular copper ions,

Phosphate ions of 5 to 30% by weight of P ₂ O ₅ , at least one accelerator of 0.2 to 5% by weight in each case,

Molybdenum ions and / or molybdenum ions from a total of 0.1 to 1% by weight, calculated as MoO ₃ , and free fluoride ions from 0.1 to 2% by weight.

The aqueous concentrate preferably also has a content of: at least one nonionic and / or anionogenic surfactant of 0.05 to 15% by weight or / and of at least one organic solubilizer each of 0.05 to 0.5% by weight or / and ions of at least one alkali metal or / and alkaline earth metal of 2 to 10% by weight, in particular of sodium ions.

The metal parts coated by the process according to the invention can be used as radiator elements, radiators, frames, plates, claddings, angles, components in the interior of vehicles or aircraft, components in apparatus and mechanical engineering.

The process according to the invention has the advantage over the previously described and practiced pretreatment processes by iron phosphating that the thickness of the first lacquer layer can be significantly reduced without the corrosion protection being impaired.

The subject matter of the invention is explained in more detail below on the basis of exemplary embodiments:

The following parameters were set in a 4-zone system:

1st zone - cleaning and phosphating: treatment time: 45 sec. Temperature: 55 ° C injection pressure: 1, 2 bar total acidity: 10 points free acidity: 0 points pH value: 4.8.

Zone 2 - cleaning and phosphating: Treatment time: 45 sec. Temperature: 50 ° C injection pressure: 1, 2 bar total acid: 3 points free acid: 0 points pH: 5.3.

The composition of the phosphating bath can have, for example, the following contents in g / L:

P ₂ O ₅ 6.2

NO ₃ 0.1

MoO ₃ 0.07

NH ₄ 0.02

NBS 0.6

"^" up to 0.2 in total

Free 0.03

Na 2.2

Fe up to 1

Zn up to 0.1

Mn up to 0.05

Cr up to 0.01

Ni up to 0.01

Cu 0.005 non-ionic surfactants 1

CO ₂ may contain coal

Acidity of the air.

The pH was adjusted by adding NaOH.

3rd zone - rinsing:

Treatment time: 30 sec.

Temperature: unheated, ie room temperature Spray pressure: 1, 2 bar Water quality: city water.

4th zone - rinsing:

Treatment time: 30 sec.Temperature: unheated, i.e. Room temperature spray pressure. 1, 2 bar

Water quality: Contaminated, fully demineralized water, in which demineralized water has taken up contaminated water from the rinsing and from the rinsing with the spray ring. The water quality is far better than city water.

5. Rinsing with spray ring:

1, 1 I demineralized water per m ² surface water quality: VEW = fully demineralized water. Then flows in a cascade to Zone 4.

6. Blow off and dip painting:

After this spray pretreatment, the pretreated metal parts were passed into a blowing zone with 4000 m ^{3 of} cold air per hour and then into the cathodic electrodeposition coating, where the pretreated metal parts were coated at 22 ° C. for 90 seconds.

substrates:

The substrates to be coated were made of normal St 370 structural steel and had various geometric shapes, as are customary for the design of radiators. A radiator that was particularly problematic for coating was selected: Type 22 radiators 600 mm high and 1000 mm wide. The type 22 has two external water channels made of structured plates and two internal convector sheets. This means that it has a large number of shielded areas.

The task was to coat the surfaces of the convectors. The convectors, since they are on the inside, represent Faraday cages. In addition, the task was to keep the paint weight, ie also the paint layer averaged over the entire surface, as low as possible.

To check the results, the radiators were weighed in the dry state before and after the cathodic dip coating. In the current series, the dip coat thickness was also measured. However, since these measurements had to be limited to the elements of the water channels, that is to say the outer elements, and could only be carried out selectively, the measurement results can only be evaluated approximately.

Results:

Example 1 (comparative examples):

With the same bath parameters for phosphating, two type 22 radiators were pretreated in a first production line and in a parallel production line without being subsequently painted in the line. After drying, the pretreated metal parts were weighed and then all four radiators in the first production line were dip-coated under identical conditions in order to avoid different settings of different paint baths.

In this first cross-test, all 4 radiators had coating weights of 142 to 148 g with a surface area of 7.8 m ² . Example 2 (according to the invention or comparative example):

In the second cross-test between the first production line and the parallel production line, 3 mg / l copper was added to the phosphating baths of the first production line as copper nitrate, but not in the parallel production line.

Before the second cross-test, butyl glycol was also added to all paint baths to improve the paint flow, which is usually led to increased layer weights.

The coating layer weights of the radiators pretreated with the copper-containing phosphating solution were reduced to 120 g in the example according to the invention, while the reference heating elements of the parallel production line (comparative example) had coating layer weights of 162 g and 165 g. As expected, the addition of butyl glycol had an effect on the reference radiators with increasing layer weights, but not on the radiators pretreated according to the invention. Rather, in the radiators pretreated according to the invention, despite the addition of butyl glycol, there was a significant reduction in the layer weight.

Claims

claims

1. A method for coating metal surfaces with a pretreatment layer prior to the deposition of a thin electrocoat, characterized in that a pretreatment layer based on iron phosphate / iron oxide / iron hydroxide containing copper, silver, gold, platinum, iridium, osmium, palladium, rhodium or / and ruthenium is deposited.

2. The method according to claim 1, characterized in that an aqueous solution is used for the deposition of the pretreatment layer, which contains ions of copper, silver, gold, platinum, iridium, osmium,

Palladium, rhodium and / or ruthenium in the range of 0.2 to 40 mg per liter, in particular a content of copper ions.

3. The method according to claim 1 or 2, characterized in that the aqueous solution for the deposition of the pretreatment layer has a phosphate content in the range of 1 to 10 g per liter.

4. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer has a content of alkali metal and / or alkaline earth metal ions, in particular sodium, in the range from 0.3 to 3.5 g per liter.

5. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer has an ammonium ion content in the range of 2 to 50 mg per liter.

6. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer has a free fluoride content in the range of 0 to 400 mg per liter.

7. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer has a content of molybdenum ions and / or molybdate in the range from 0 to 500 mg per liter, calculated as MoO ₃ .

8. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer has a content of nitrate ions in the range of 0 to 5 g per liter.

9. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer contains at least one nonionic and / or anionogenic

Has surfactant in the range of 50 to 5000 mg per liter.

10. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer has a content of at least one organic solubilizer in the range of 0 to 200 mg per liter.

1 1. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer contains at least one accelerator, in particular an accelerator selected from the group of nitroguanidine, chlorate ions and NBS ions in the range from 0 to 3 g per liter.

12. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer has a temperature in the range of 30 to 70 ° C.

13. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer has a pH in the range from 3.5 to 6.5.

14. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer has a total acid number in the range from 2 to 20.

15. The method according to any one of the preceding claims, characterized in that the aqueous solution for the deposition of the pretreatment layer has a free acid content of up to 2 points.

16. The method according to any one of the preceding claims, characterized in that metal parts are coated in particular of complex geometry, preferably metal parts made of iron or steel materials, aluminum or aluminum alloys, magnesium alloys or galvanized metal parts.

17. The method according to any one of the preceding claims, characterized in that pretreatment layers are deposited from the aqueous solution, on which lacquer layers with a layer thickness of 0.5 to 20 microns are applied by cathodic or anodic dip coating.

18. The method according to any one of the preceding claims, characterized in that in addition to the immersion lacquer layer, a lacquer layer or a

19. Aqueous concentrate for preparing an aqueous solution for the deposition of a pretreatment layer, characterized in that the concentrate has the following contents:

Ions of copper, silver, gold, platinum, iridium, osmium, palladium, rhodium and / or ruthenium each from 0.005 to 0.4% by weight, phosphate ions from 5 to 30% by weight P ₂ O ₅ , at least one accelerator from 0.2 to 5% by weight, molybdenum ions and / or molybdenum ions from a total of 0.1 to 1% by weight, calculated as MoO ₃ , and free fluoride ions from 0.1 to 2% by weight; preferably also additionally contains at least one nonionic and / or anionogenic surfactant in each case from 0.05 to 15% by weight or / and at least one organic solubilizer in each case from 0.05 to 0.5% by weight or / and from at least one alkali metal and / or alkaline earth metal ion of 2 to 10% by weight, in particular sodium.

20. Use of the products produced by the process according to claims 1 to 18 as radiator elements, radiators, frames, plates, panels, angles, components in the vehicle or aircraft interior, components in apparatus and mechanical engineering.