DE4214992A1 - Copper-containing nickel-free phosphating process - Google Patents

Abstract

A process is disclosed for producing copper-containing, nickel-free phosphate layers with a defined copper content in the phosphate coatings. No pinholing is observed on the metal surface, in particular on electrolytically zinc coated steel, when an appropriate ratio between copper and nitrate is set in the phosphatizing bath.

Description

The invention relates to a process for the production of copper containing nickel-free phosphate coatings on metal surfaces as well the application of the method as a pretreatment of Metalloberflä before painting, in particular a cataphoretic Dipcoating (KTL).

The quality of phosphate coatings before a cataphoretic immersion Paint (KTL) depends on a variety of parameters. To include physical quantities such as shape and size of the crystals whose mechanical stability and in particular the free metal surface after phosphating, the so-called pore surface. At the che mixing parameters are of particular interest to Alkalistabi quality during the cataphoretic coating, the bond-resistant Speed of the crystal water of the zinc phosphate crystals during firing varnishes and rehydration properties.

By using activating agents before phosphating you can control the coating weight, in particular reduce. By the oligomeric / polymeric titanium present in the activating agents phosphate are formed on the metal surface active centers, from which crystal growth proceeds. As a result he On the one hand, you keep smaller and more mechanically stable crystals, On the other hand, the pore area is reduced and thus the attack corrosive media in violation of the paint difficult.

In the prior art, it has proved to be advantageous nickel containing treatment baths to the layer quality of subsequent phosphating, especially in surface-refined Material to improve.  

Because of the toxic effect of nickel-containing dusts, the Grinding phosphated sheets can be developed as well as the sharpening requirements for the introduction of nickel-containing Ab Watering in the sewer you look for nickel-free phospha tierungslösungen.

Additions of magnesium ions were investigated. Early on, the application-technically positive effects of these ions were recognized (DE-A-39 20 296), which are based on several effects. We considerably here is the high crystal stability during heating. The release of crystal water, which weakens the crystal composite and thus the overall system, is shifted to higher temperatures with increasing magnesium incorporation. On the other hand, the crystals are smaller by additions of Mg ²⁺ ions, the phosphate layer denser and the free metal surface after phosphating is mini mized. The layer weight reduction by magnesium ions is so strong that other control variables, which are usually also used for layer weight reduction, such as very low zinc concentrations (0.6 g / l Zn ²⁺ ), high concentrations of accelerators such as sodium nitrite or meta-nitrobenzenesulfonate / Na - Salts can not be used in addition, in order not to press the area-related mass below 1.5-2.0 g / m ² .

For steel surfaces could so nickel-free phosphating on Based on zinc, manganese and magnesium ions, which Specifications of the users. For surface-finished Material were the results with these magnesium-containing methods However, they are not always satisfactory.

Thus, the influence of Cu ²⁺ ions was investigated. From DE 40 13 483 A1 a process for the phosphating of metal surfaces is known, in which one works with phosphating, which we sentlichen are free of nickel. As essential bath constituents zinc, manganese and small amounts of copper are mentioned. In addition, the concentration of Fe (II) is kept below a maximum value by oxygen and / or other similarly acting Oxi dationsmittel. The method is used in particular for the phosphating of steel, galvanized steel, alloy-galvanized steel, aluminum and its alloys for pretreatment for subsequent Lackie tion, in particular an electrodeposition coating. Additions of small amounts of copper ions to phosphating baths have been known for 40 years. Thus, in US-A 2,293,716 small amounts of Cu ²⁺ ions are added as "accelerator" or to improve the white color tone anodic electrodeposition paints as "Farbneutralisator". It was observed that copper additives increase the coating weight, especially on steel. For galvanized material, however, the occurrence of disturbing "specks" is described. "Speckling" is understood to mean the small, white efflorescence of crystals which, under the microscope, turns out to be crystals of crystals of zinc phosphate accumulated at the edge (see W. Rausch: "The Phosphatization of Metals", 2nd ed., 1988, Leukze et al. Verlag, Saulgau, p. 108). The Stippenbil tion is particularly pronounced for longer treatment times, for example, in plants, standstill.

It was therefore the object of a process for the preparation of copper-containing nickel-free phosphate coatings available in the absence of nickel on metal surfaces such as cold rolled steel, electrolytically galvanized steel and aluminum very good Paint adhesion and excellent corrosion protection guaranteed and in particular the formation of specks on galvanized steel ver avoids.  

The above object is achieved by means of a spe originally selected phosphating solution, with which it is possible kup Ferated phosphate layers with a defined copper content while avoiding the formation of specks.

The investigations had surprisingly shown that the occurrence of so - called "specks" both from the concentration of the Copper as well as the concentration of nitrate in the phosphating bath depends. The product of the two concentrations (in mg / l) may ei limit value not exceeding 50 000 for diving procedures and in spraying is 15,000.

The present invention is thus in a first Embodiment A method for producing copper-containing nickel-free phosphate layers containing copper in Be rich of 0.5-5 wt .-% on metal surfaces with a phospha animal solution containing

Zinc | 0.2 - 2 g / l, copper 0.5-25 mg / l, phosphate 5.0 - 30 g / l (calculated as P₂O₅), nitrate 0.1 to 15 g / l,

wherein the product of the components contained in the phosphating solution on Cu ions (in mg / l) and nitrate ions (mg / l) when using Dipping process smaller than 50 000 and using spray gun drive is less than 15 000's.

It has been found that these Phosphatierlösungen also in Abwesen of nickel on metal surfaces as mentioned above, without stip very good paint adhesion and an excellent corrosi ensure protection. The Zinkphosphatschich thus prepared  Th are small (0.5-10 microns), compact, dense Built up crystals. In particular, was in the investigation kup Ferionhaltiger phosphatizing found that only very small Amounts of copper (II) ions in the solution are required to complete the desired copper content of the phosphate layer in the range of 0.5-5 Adjust% by weight. It was found that when exceeded the copper amount of more than 5 wt .-% of the phosphate layer specks education found on electrolytically galvanized steel surfaces has been.

In a further embodiment of the present invention it is Therefore, it is preferred that the phosphating solution contain 5-20 ppm copper (II) Contains ions when the metal surface by dipping with the phosphating solution is brought into contact. When using the Injection process, it is equally preferred that the Phos 1 to 10 ppm of copper (II) ions to give Incorporate the copper content in the conversion coating, without the disturbing specks on electrolytically galvanized steel surfaces too produce.

To ensure proper phosphate layer formation, It is known to increase the pH of the phosphating solution to a value between 3.0 and 3.8. If necessary, be to Adjusting the pH of the phosphating solution further cations, for example, alkali metal cations and / or alkaline earth metal cat ions with corresponding anions known in the art used. Corrections of pH during phosphating For example, may be vorgenom by basic additives or acids be men.

The inventive method can in particular on steel, ver zinc-plated steel, alloy-galvanized steel, aluminum and its  Alloys are applied. The term steel in the sense of before underlying invention also includes white low alloyed steels unalloyed steels and higher and high-strength steels. Wesentli Contents of the invention is that the aqueous, acidic phospha Animal solutions are free of nickel. However, this means that under technical conditions a small amount of nickel (II) ions in may be included in the phosphating. However, this amount is intended in accordance with the prior art DE 40 13 483 A1 we less than 0.0002-0.01 g / l, especially less than 0.0001 g / l be.

When applying the Phosphatierverfahrens on steel surfaces Iron is dissolved in the form of iron (II) ions. By adding suitable oxidizing agents iron (II) is converted into iron (III) and can be precipitated as iron phosphate sludge.

To limit the iron (II) ion concentration are a number of Oxidizing agents known in the art. Thus, for example example, the contact of the phosphating with oxygen, for example Wise atmospheric oxygen and / or the addition of suitable Oxidationsmit tel for limiting the iron (II) ion concentration. In the sense of the present invention are the oxidizing agents of phosphating solutions selected from nitrite, chlorate, hydroxylamine and its Salts, bromate, permanganate, peroxide compounds (in particular Hydrogen peroxide, perborate, percarbonate, perphosphate) and orga niche nitro compounds, in particular nitrobenzenesulfonate. The Amounts of oxidizing agents to be used are known from the prior art Technique known. For example, sodium nitrite may be 0.1-0.5 g / l, peroxide compound calculated as hydrogen peroxide: 0.005- 0.1 g / l, nitrobenzenesulfonate: 0.005-1 g / l. These as "Beschleu niger "known oxidizing agents continue to have the task To "depolarize" metal surface during acid attack, d. H. the  Prevent formation of elemental hydrogen thereby preventing the hydrogen ions the accelerators are reduced.

The addition of manganese (II) ions are particularly in the fuel zen on surface refined materials fine crystals out forms, which hardly show the known needle structure, but have a much more compact granular morphology. The Use of manganese ions besides zinc ions in low-zinc-phospha animal method improves corrosion protection, especially at Use of surface-refined thin sheets. The installation of manganese in the zinc phosphate coatings leads to smaller and more compact Crystals with increased alkali stability. Accordingly exists a particularly preferred embodiment of the present invention in that the phosphating solution contains 0.1-5 g / l, in particular 0.5- Contains 1.5 g / l manganese (II) ions.

The quality of herge with the aid of the method according to the invention copper-containing nickel-free phosphate coatings will not impaired if the phosphating solution up to 2.5 g / l, Erdal potassium cations, in particular magnesium and / or calcium ions, for example, contains from the process water.

The use is known in principle from the prior art of modifying compounds from the group of surfactants, Hydroxycarboxylic acids, tartrate, citrate, hydrofluoric acid, alkali metal fluoro ride, Bortetrafluoride, Silicofluoride. While the addition of Ten siden (for example, 0.05-0.5 g / l) to improve the Phosphation of slightly greased metal surfaces leads is it is known that hydroxycarboxylic acids, in particular tartaric acid, Ci tronensäure and their salts in a concentration range of 0.03-0.3 g / L to a significant reduction of the phosphate layer contribute weight. Fluoride ions promote phosphating  of more vulnerable metals, leading to a Ver shortening of the phosphatizing and beyond to an increase the area coverage of the phosphate layer. As you know, you bet about 0.1-1 g / l of said fluorides. Through the kontrol The added addition of fluorides will also make the training more crystalline Phosphate layers on aluminum and its alloys possible. Salts of boron tetrafluoride and silicon hexafluoride increase the Ag Gressivität the phosphating, which is particularly in the Treatment of hot-dip galvanized or aluminum surfaces noticeable makes why these complex fluorides, for example, in amounts of 0.4-3 g / l can be used.

Typically, phosphating at temperatures of Baths applied between 40 and 60 ° C. These temperature ranges are used in both spraying and spraying diving and diving ap plications used.

For economic reasons, the treatment of the upper areas chosen as short as possible; for example, are impact times of 1 to 5 minutes are sufficient to cover an evenly de phosphate layer to produce. For galvanized steel it is be know that even contact times of less than 1 minute is sufficient are to produce uniformly covering phosphate layers. the Accordingly, the method is also in fast-running Bandan lay usable. In such systems, however, occur relatively frequently fig downtime, so that it happens that the Metallober make contact with the phosphating solution for a much longer time stay. This can be the case with galvanized substrates to the above lead to harmful specks. When applying the erfindungsge However, these disadvantages can be avoided according to the method.

The to be phosphated metal surfaces are in per se im Prior art known prior to phosphating ge cleans, rinses and if necessary with activating agents, especially treated on the basis of titanium phosphates.  

Examples process transition

• 1. Degrease with a mild alkaline cleaner (RIDOLINE® 1558)
  Approach: 2%
  Temperature: 55 ° C
  Time: 4 min.
• 2. Rinse with process water
  Temperature: room temperature
  Time: 1 min.
• 3. Activation with an oligomeric / polymeric titanium phosphate-containing activating agent (Fixodine® 950)
  Approach: 0.1% in demineralized water
  Temperature: room temperature
  Time: 1 min.
• 4. phosphating with each of the examples and comparative examples mentioned solution
  Approach: see examples
  Temperature: 53 ° C
  Time: according to example.
• 5. Rinse with process water
  Temperature: room temperature
  Time: 1 min.
• 6. Post-passivation with a commercially available chromium-containing post-passivation (DEOXYLYTE® 41)
  Approach: 0.1% by volume
  Temperature: 40 ° C
  Time: 1 min.
• 7. Rinse with demineralized water

example 1

Starting from an aqueous solution with a bath composition in Step 4 of the above procedure from

Zn (II) | 1,1 g / l Mn (II) 0.8 g / l Cu (II) 0.015 g / l PO₄³⁻ 17.5 g / l NO _3- 2.0 g / l SiF₆²⁻ 0.95 g / l F⁻ 0.2 g / l @ Accelerator: Hydroxylammonium sulfate 1.7 g / l Total acidity: 22.7 points Free acid: 0.9 points

were at a temperature in the range of 52 to 54 ° C in the course of 3 minutes a surface of sheet steel (Sidca) (Example 1a) and electrolytically galvanized sheet (ZE) (Example 1b) phosphated and the corrosion protection data shown in Table 1 hold.

Comparative Example 1

Starting from an aqueous solution with a bath composition in Step 4 of the above procedure from

Zn (II) | 1.0 g / l Mn (II) 1.4 g / l PO₄³⁻ 16.9 g / l NO _3- 2.0 g / l SiF₆²⁻ 1.0 g / l F ^- 0.2 g / l Accelerator: (Hydroxylammonium sulphate 1.8 g / l, Total acidity: 21.8 points Free acid: 0.9 points

were at a temperature in the range of 52 to 54 ° C in the course of 3 minutes a surface of sheet steel (Sidca) (Comparative Example 1a) and electrolytically galvanized sheet (ZE) (Comparative Example 1b) phosphated and reproduced in Table 1 Korro protection data.

Comparative Example 2

Starting from an aqueous solution of a bath composition in Step 4 of the above procedure from

Zn (II) | 1.0 g / l Mn (II) 0.7 g / l Ni (II) 0.9 g / l PO₄³⁻ 17.3 g / l NO _3- 3.5 g / l SiF₆²⁻ 0.25 g / l Accelerator: (NaNO₂) 0.15 g / l Total acidity: 21.7 points Free acid: 1.1 points

were at a temperature in the range of 52 to 54 ° C in the course of 3 minutes a surface of sheet steel (Sidca) (Comparative Example 2a) and electrolytically galvanized sheet (ZE) (Comparative Example 2b) and the anti-corrosion data presented in Table 1 receive.

The corrosion protection effect of the phosphating according to the invention was in accordance with the standards of the Association of the Automotive Industry e.V. (VDA 621-414 (outdoor weathering) and VDA 621-415 (alternating climate)) certainly.

The examination of the corrosion protection of automotive coatings by weathering the determination of the corrosion protection serves effect of automotive coatings under the influence of the natural weathering with additional stress by spraying with saline.

Test struts consisting of a typical car body design KTL, filler, topcoat white, each with a specification parallel to the long side with a straight, controlled until the Metal background provided by continuous Ritzspur. The trial  strokes are stored on suitable racks. They will be rich once in a while with a dilute sodium chloride solution sprayed.

The test time in the present case was 6 months.

For final evaluation, the test strokes with clear, flowing Rinsed with water, possibly dry with compressed air on the surface blown and looked at visible changes. The Ritz to both sides outgoing visible rust is fixed provides. The width of the next to the Ritz damaged by rust Me tall surface is generally easy on the paint surface recognize. For evaluation, the average total width of the undercut zone measured in mm. This is the width of meh measured and the arithmetic mean.

The examination of the corrosion protection of automotive coatings cyclically changing stress serves to prevent corrosion Protection of automotive coatings with a time-lapse laboratory Procedures to assess which corrosion processes and corrosion images causes the resulting with the driving operation well ver are equal. The short test simulates in particular those of ei undermining, as well as the marginal and Edge rusting on special corrosion test sheets or components with known weak spots of the paint and the surface rust.

Analogous to the investigations of the outdoor weathering were also here Test plates parallel to the longitudinal side with a straight to the Me provided talluntergrund continuous scratch track.

The test plates were placed in the tester at an angle of 60 ° to Set at 75 ° to the horizontal.  

A test cycle lasts 7 days and consists of

1 day = 24 h salt spray test SS DIN 50 021
4 days = 4 cycles of condensed water exchange climate KFW DIN 50 017 and
2 days = 48 h room temperature 18 ° to 28 ° C according to DIN 50 014.

The test time is 10 cycles corresponding to 70 days.

After completion of the test, the test plates are given a clear, rinsed with running water, if necessary with compressed air surface blown dry and looked at visible changes. The visible from the Ritz to both sides outgoing visible rust is determined.

In general, the width of next to the scratch by rust be damaged rust surface as a blister or rust trace on the paint surface easily recognizable. In addition, with an oblique ge holding knife blade, z. B. with an eraser, the unterroste Carefully remove the paint film until it is still firmly adhering be removed.

For evaluation, the average total width is also used here of the undercut zone measured in mm. This is the width of meh reren places measured and formed the ariethmetische mean.  

Table 1

Corrosion Test Results

3-layer paint system

Example 2

To investigate the influence of Cu and nitrate concentrations and the Phosphatierzeit on the speckling in diving at prolonged treatment times were sheet steel (Sidca) and electrolytically galvanized sheet (ZE) with phosphating solutions of the following composition at a temperature of 53 ° C for 10 Phosphated for a few minutes:

Zn (II) | 1.0 g / l Mn (II) 0.8 g / l PO₄³⁻ 17.5 g / l SiF₆²⁻ 0.95 g / l F⁻ 0.2 g / l Cu (II) 0 - 35 ppm NO _3- 0-10 g / l Accelerator: Sodium nitrite 0.15 g / l Free acid at pH 3.6: 0.9 points Total acidity: 21.5 points

Hereby, the following results were obtained which are shown in Table 2.  

Table 2

Comparative Example 3

Table 3 shows a comparative experiment without nitrate at 4 min Be treatment time.  

Table 3

Example 3

To investigate the influence of Cu and nitrate concentrations on the speckling by spraying were electrolytic Galvanized steel sheets (ZE) 2 min at 50-55 ° C with the following Phosphating bath concentrations treated:

Zn²⁺ | 0.8 g / l Mn²⁺ 0.7 g / l PO₄³⁻ 16.5 g / l SiF₆²⁻ 0.2 g / l F⁻ (free fluoride) 0.1 g / l Cu²⁻ 0-35 mg / l NO _3- 2-5 g / l Accelerator: Sodium nitrite 200 mg / l   Free acid at pH 3.6: 0.6 Total acid at pH 8.5: 22.0

The results listed in Tab. 4 were obtained:

Table 4

Claims (9)

1. A process for the preparation of copper-containing nickel-free phosphate layers containing copper in the range of 0.5 to 5.0 wt .-% on metal surfaces with a phosphating ent holding Zinc | 0.2 - 2 g / l copper 0.5-25 mg / l phosphate 5.0 - 30 g / l (calculated as P₂O₅) nitrate 0.1-15 g / l, the product of the amounts of copper ions (in mg / l) and nitrate ions (in mg / l) contained in the phosphating solution being less than 50,000 when using dipping processes and less than 15,000 when spraying is used. 2. The method according to claim 1, characterized in that the Phosphating solution using dipping method 5-20 ppm Kup Fer (II) ions and when using spraying 1-10 ppm Contains copper (II) ions. 3. The method according to claim 1 or 2, characterized that the phosphating solution 0.15-5 g / l, in particular 0.5-1.5 g / l Contains manganese (II) ions. 4. Method according to one or more of claims 1 to 3, characterized in that the phosphating alkaline earth metal ions, in particular magnesium and / or calcium ions in an amount of up to 2.5 g / l.   5. The method according to one or more of claims 1 to 4, characterized in that the oxidizing agent of the phosphating solution is selected from nitrite, chlorate, hydroxylamine and its Salts, bromate, peroxide compounds, organic nitro compounds, in particular nitrobenzenesulfonate. 6. The method according to one or more of claims 1 to 5, characterized in that the metal surface is selected from Steel, galvanized steel, alloy galvanized steel, aluminum and its alloys. 7. The method according to one or more of claims 1 to 6, characterized in that the metal surface with the Phos phatierlösung by spraying, dipping or spray diving in Kon clock brings. 8. The method according to one or more of claims 1 to 7, characterized in that the metal surface of galvanized or alloy-galvanized steel. 9. Application of the method according to one or more of Proverbs 1 to 8 as a pretreatment of the metal surface in front of a Painting, in particular a cataphoretic dip painting.