DE10006338C2 - Process for coating metal surfaces, aqueous concentrate therefor and use of the coated metal parts - Google Patents

Description

The invention relates to a method for coating metal surfaces with a pre-treatment layer before depositing a thin electro dip coating, an aqueous concentrate for the preparation of the aqueous solution solution for the deposition of the pretreatment layer and the use of the Products manufactured by the process according to the invention.

Process for the preparation of iron phosphate coatings as pretreatment Basically, coating layers before painting are well known.

Generally, iron phosphate coatings are used as pretreatment layers Before painting, made by contact with an acidic aqueous mono- or / and phosphating solution containing orthophosphate and subsequently by electrocoating the entire metal surface and often also by subsequent powder coating of the surfaces that are easily accessible from the outside games. These processes are being pushed to the max today. Here is on strived to make these processes more reliable and cost-effective The comparatively thick electrical system accounts for a significant proportion of the costs Dipping lacquer layer, which is usually used today in the case of complicated structures, rear cuts and / or concealed metal parts such as. B. some radiator elements still as an average over the entire Surface is at least 12 microns, often more than 15 microns. Because because of the hin Cuts or hidden cavities often have to be approx. 250 V instead of approx. 40 V can be used for electro-dipping, even in the bad accessible areas (Faraday cage) to a closed paint application enable. Here is on the easily accessible and therefore easy to paint Parts of the metal parts are coated with an unnecessarily thick electrocoat. It would be sufficient if a continuous, namely a so-called.  stratified electrocoat layer was achieved. The reduction in The thickness of the electrocoat layer by an average of only 1 µm can be in the paint shops already lead to six-figure DM savings per year.

DE-A1-195 44 614, DE-A1-40 13 483, DE-A1-195 40 085 and DE-A1-196 34 732 describe zinc phosphating processes that differ from iron phosphating processes fundamentally differentiate. These publications teach zinc levels in the area of 0.2 to 3 g / L and therefore concern the low zinc phosphating. Zinkphos phat layers usually consist predominantly or entirely of Huréaulith, Phosphophyllite, Scholzit and / or Hopeit, during iron phosphate layers mainly composed of iron phosphate, iron oxide and / or iron hydroxide are.

Surprisingly, it was found that an addition of ions from copper and che a mixture of related metals to the phosphating solution a pretreatment layer allowed to form on which the deposition of the electrocoat is accelerated and equalized. In the area of the undercuts or hidden cavities is the paint deposition in the invention Process significantly better compared to the easily accessible areas 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 altogether thinner than in the prior art to apply without the Kor to impair corrosion protection.

The task is accomplished by a process for coating metal surfaces with a pre-treatment layer before depositing a thin electro Dip coating layer solved, in which a pre-treatment layer based on iron phosphate / iron oxide / iron hydroxide containing copper, silver, gold, platinum  Platinum, iridium, osmium, palladium, rhodium and / or ruthenium deposited becomes.

Claims 2 to 18 further develop the method. The task continues dissolved by an aqueous concentrate according to claim 19.

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

The effect of the ions of copper or the other precious metals mentioned is not fully understood yet. This may result in local elements te on the surface, which reduce the electrical resistance and the Accelerate the process of electrodeposition. In addition, through this additive achieves even higher temporary corrosion protection.

The content of phosphate in the phosphating solution can range from 1 to 10 g per liter are preferably from 2 to 8 g per liter, particularly preferably from 3.5 to 5.5 g per liter. The addition of the phosphate, especially to one Concentrate, preferably done by adding orthophosphoric acid.

The phosphating solution preferably has an ion content of min at least one alkali metal and / or alkaline earth metal, especially 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 when adjusting the pH and is preferred to the phosphoric acid prevented. The sodium ions can, for example, by adding sodium hydroxide are introduced.

The phosphating solution preferably has an ammonium 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 ⁰ 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 content NEN in the range of 0 to 400 mg per liter, preferably from 1 to 350 mg per liter, particularly preferably from 50 to 300 mg per liter. The addition of flu oride is preferably carried out 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 content of nitrate ions 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 nitrate ion content enables light an increase in the pickling attack, an equalization of the phosphate layer formation and accelerates.

The phosphating solution preferably has at least one egg content non-ionic and / or anionic surfactant in the range from 50 to 5000 mg per liter, preferably from 100 to 4000 mg per liter, especially before increases from 200 to 3000 mg per liter. These surfactants provide the better benet of the metal surface and thus for the more uniform removal of or ganic impurities on the metal surface, for the more uniform Stain attack on the metal surface and for the more uniform phosphate layer training on the metal surface.

The phosphating solution preferably has at least one egg content 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 solubilizer serves that the surfactants in one component remain in the aqueous solution.

The phosphating solution preferably has at least one egg content nem accelerator, in particular an accelerator selected from the Group of nitroguanidine, chlorate ions and NBS ions in the range of 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 Value range, so that you can work in a wider pH range.

The phosphating solution advantageously has for environmental reasons protection no or only a low content of nitrite ions, chromium ions, Nic celions, cobalt ions, manganese ions and cadmium ions. If the bath egg should have a higher content of at least one of these substances, the processed solution u. U. elaborate disposal can be arranged. Furthermore, the phosphating solution preferably has for reasons of corrosion protection of the metal parts to be coated also contains no chloride and sulfate ions.

Certain levels of aluminum in the phosphating solution can U. to Precipitation of cryolite, calcium and others. U. for the precipitation of calcium flu lead orid. It is therefore advantageous to keep such ions within such limits hold in which precipitation can be avoided or kept to a minimum.

The phosphating solution preferably has a temperature in the range of 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 of 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 Phosphating solution diluted to 50 ml with deionized water, titrated with 0.1 normal sodium hydroxide solution up 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 Phosphating solution diluted to 50 ml with deionized water, is titrated with 0.1 normal sodium hydroxide solution up to a pH of 4.2, whereby KCl is then added to the sample to be titrated to saturation if in the sample contains complex-bound fluoride to dissociate it prevent as much as possible.

As water quality for the phosphating solution as well as for the aqueous one Concentrate, which can be used both to turn on and to supplement the phosphate Solution can be used are city water, which is of higher hardness grade is preferably decarbonized, but also purer water quality ten such as B. 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 solution - rinsing with water
• b) cleaning and phosphating with the phosphating solution according to the invention solution - rinsing with water - rinsing with water
• c) pre-cleaning with a first phosphating solution according to the invention - Cleaning and phosphating with a second phospha according to the invention solution - rinsing with water - rinsing with water.

For the step of cleaning and phosphating is preferably with a Spray time over 0.5 to 4 minutes, in particular over 0.8 to 3 minutes, completely especially over 1 to 2 minutes with a spray pressure in the range of 0.3 to 2.5 bar worked. Alternatively, the metal parts can be placed in a bath over time from 1 to 10 minutes, especially over 1.5 to 6 minutes. at The times mentioned refer to a process with a 4-zone system on the sum of the pre-treatment times for pre-cleaning / phosphating and Cleaning / phosphating.

As in c), cleaning and phosphating can also be done directly in two following baths are carried out: It is recommended to take the first bath set a higher total acid score than in and after the second bath ensure that the free acid content in both baths is as low as possible.

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

Rinsing can last for 20 to 80 seconds with a spray pressure of 0.3 up to 2.5 bar. Deionized water is preferably used here. Here, the salt load should be taken by suitable measures such. B. downstream th spray ring with deionized water as much as possible.  

After the last spraying step, the drained water should have a value of electri conductivity due to the subsequent electrocoating of Do not exceed 50 µS / cm.

Usually, the metal parts pretreated in this way are transferred directly to the elec Trotauchlack system retracted. Drying can then be omitted.

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

The pretreatment layer, even if ions released from the metal surface are involved in the layer structure, can be referred to as a conversion layer. 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 of 0.15 to 0.4 μm, and a weight per unit area of 0.1 to 1.2 g / m ² , preferably of 0.2 to 0.8 g / m ² . It is advantageously amorphous.

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

Paint 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 prior art, the first immersion lacquer 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 lacquer layer of 1.5 g / cm ^{3, means} an average layer thickness in Corresponds to the range of 12 to 15 microns, or even higher layer weights, while in the process according to the invention on similar metal parts with hidden areas, a layer weight is approximately in the range of 12 to 17.5 g / m ² , which assumes a density of the branded Lacquer layer of 1.5 g / cm ³ corresponds to an average layer thickness in the range from 8 to 11.7 µm.

Such an immersion lacquer layer can additionally include a lacquer layer or a different organic-containing coating and / or an adhesive layer in particular special with painted metal parts such. B. applied in the form of plates the. The additional layer of lacquer usually has decorative functions and slightly improves corrosion protection; it is often done by powder coating ren applied.

With an adhesive layer that is preferably applied to the additional lacquer layer is brought, metal or plastic parts can be glued, the advantageous t are also pretreated and / or painted. These glued parts ha ben z. B. 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 each from 0.2 to 5% by weight,
Molybdenum ions and / or molybdenum ions totaling 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, each from 0.05 to 15% by weight
or / and of at least one organic solubilizer each from 0.05 to 0.5% by weight
or / and ions of at least one alkali metal and / or alkaline earth metal each of 2 to 10% by weight, in particular of sodium ions.

Leave the metal parts coated by the method according to the invention itself as radiator elements, radiators, frames, panels, cladding, win kel, components in the vehicle or aircraft interior, components in Use apparatus and mechanical engineering.

The method according to the invention has compared to the previously described and pretreatment processes by iron phosphating have the advantage that the thickness of the first layer of lacquer can be significantly reduced without corrosion protection is impaired.

The subject matter of the invention will be explained in the following with the help of embodiments play explained in more detail:

The following parameters were set in a 4-zone system 1st zone - cleaning and phosphating

Treatment time: 45 sec.
Temperature: 55 ° C
Spray pressure: 1.2 bar
Total acidity: 10 points
Free acidity: 0 points
pH: 4.8.

Zone 2 - cleaning and phosphating

Treatment time: 45 sec.
Temperature: 50 ° C
Spray pressure: 1.2 bar
Total acidity: 3 points
Free acidity: 0 points
pH: 5.3.

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, ie room temperature
Injection 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. Rinse with spray ring

1.1 l demineralized water per m ²

surface
Water quality: VEW = 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 structural steel St 370 and has different geometric shapes, such as those used to design radiators are common.

A particularly problematic radiator was coated chooses: Type 22 radiators 600 mm high and 1000 mm wide. The guy 22 each has two external water channels made of structured plates and two internal convector sheets. As a result, he has a lot number of shielded areas.

The task was to coat the surfaces of the convectors. The convectors, since they are inside, represent Faraday cages. Also there was the task of coating weight, including the over the entire surface surface, to keep it as low as possible.

To check the results, the radiators were dry in each case stood weighed before and after the cathodic dip painting. In the run The dip coating thickness was also measured in the series. That I however, these measurements refer to the elements of the water channels, i.e. the outer ones  Elements, had to be limited and only carried out selectively the measurement results can only be evaluated approximately.

Results Example 1 (Comparative Examples)

With the same bath parameters of phosphating, two radiators were used Type 22 in a first production line and in a parallel production line pretreated 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 under identical conditions dip-coated to different settings of different paint baths avoid.

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 was 3 mg / l each for the phosphating baths of the first production line, Copper added as copper nitrate, but in the parallel production line Not.

Before the second cross-test, all paint baths were also used for the purpose of ver Improvement of the varnish course Butylglycol added, which i. d. R. to increase Layer weights led.

The coating layer weights of the copper-containing phosphating solution are over acted radiators were reduced in the example according to the invention  120 g, while the reference radiator of the parallel production line (Comparative example) had coating layer weights of 162 g and 165 g. The The addition of butyl glycol had turned out as expected in the reference radiators impacted with increasing layer weights, but not with the fiction according to pre-treated radiators. Rather, the invention has pretreated radiators significantly reduced despite the addition of butyl glycol tion of the layer weight.

Claims (20)

1. A method of 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 for the deposition of the pretreatment layer is used contains ions of copper, silver, gold, platinum, iridium, osmium, pal ladium, rhodium and / or ruthenium in the range of 0.2 to 40 mg per liter has, in particular a content of copper ions. 3. The method according to claim 1 or 2, characterized in that the water solution for the deposition of the pretreatment layer Has phosphate in the range of 1 to 10 g per liter. 4. The method according to any one of the preceding claims, characterized net that the aqueous solution for the deposition of the pretreatment layer contains alkali metal and / or alkaline earth metal ions, in particular special of sodium, in the range of 0.3 to 3.5 g per liter. 5. The method according to any one of the preceding claims, characterized net 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 having.   6. The method according to any one of the preceding claims, characterized net that the aqueous solution for the deposition of the pretreatment layer contains a free fluoride in the range of 0 to 400 mg per liter having. 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 of 0 to 500 mg per liter, calculated as MoO ₃ . 8. The method according to any one of the preceding claims, characterized in net that the aqueous solution for the deposition of the pretreatment layers a content of nitrate ions in the range of 0 to 5 g per liter has. 9. The method according to any one of the preceding claims, characterized net that the aqueous solution for the deposition of the pretreatment layer contains at least one nonionic and / or anionic Has surfactant in the range of 50 to 5000 mg per liter. 10. The method according to any one of the preceding claims, characterized net that the aqueous solution for the deposition of the pretreatment layer contains at least one organic solubilizer in the Has a range from 0 to 200 mg per liter.   11. The method according to any one of the preceding claims, characterized in net that the aqueous solution for the deposition of the pretreatment layer contains at least one accelerator, in particular egg accelerator selected from the group of nitroguanidine, chloratio NEN and nitrobenzenesulfonic acid ions in the range of 0 to 3 g per liter has.   12. The method according to any one of the preceding claims, characterized in net 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 net 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 net that the aqueous solution for the deposition of the pretreatment layer has a total acid score in the range of 2 to 20. 15. The method according to any one of the preceding claims, characterized in net 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 net that metal parts coated in particular of complex geometry the, preferably metal parts made of iron or steel materials, aluminum or aluminum alloys, magnesium alloys or galvanized metal divide. 17. The method according to any one of the preceding claims, characterized in net that pretreatment layers shot from the aqueous solution on which paint layers with a layer thickness of 0.5 to 20 µm who applied by cathodic or anodic dip painting the. 18. The method according to any one of the preceding claims, characterized in net that in addition to the immersion lacquer layer, a lacquer layer or some other kind  Organic coating or / and an adhesive layer in particular special with painted metal parts such as in the form of plates is applied. 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 of 5 to 30% by weight of P ₂ O ₅ ,
at least one accelerator selected from the group of nitroguanidine, chlorate ions and nitrobenzenesulfonic acid ions, each from 0.2 to 5% by weight,
Molybdenum ions and / or molybdenum ions totaling 0.1 to 1% by weight, calculated as MoO ₃ , and
free fluoride ions from 0.1 to 2% by weight. 20. Use of the method according to claims 1 to 18 ago provided products as radiator elements, radiators, frames, plates, Fairings, angles, components in the vehicle or aircraft interior rich, components in apparatus and mechanical engineering.