EP1060290A1

EP1060290A1 - Aqueous solution and method for phosphatizing metallic surfaces

Info

Publication number: EP1060290A1
Application number: EP99911702A
Authority: EP
Inventors: Peter Schubach; Joachim Heitbaum; Thomas Kolberg; Margit Fleischhacker-Jeworrek; Peter Jörns; Michael Deemer; Ralf Stickler; Jürgen SPECHT; Michael Lenhard
Original assignee: Chemetall GmbH
Current assignee: Chemetall GmbH
Priority date: 1998-02-27
Filing date: 1999-02-24
Publication date: 2000-12-20
Anticipated expiration: 2019-02-24
Also published as: EP1060290B1; KR20010041417A; DE59902751D1; DE19808440C2; AU3029899A; AU740987B2; DE19808440A1; ATE224466T1; SI20378A; BR9909236A; PL342623A1; JP2002505378A; SK12352000A3; TR200002495T2; CN1292041A; CA2325012A1; WO1999043868A1; US6497771B1

Abstract

An aqueous solution contains phosphate for producing layers of phosphate on metal surfaces selected from the group consisting of iron, steel, zinc, zinc alloys, aluminum and aluminum alloys. The solution contains 0.3 to 5 g Zn2+/1, 0.1 to 2 g nitroguanidine/1 and 0.05 to 0.5 g hydroxylamine/l, with an S-value amounting to 0.03 to 0.3 and the ratio of the weight of Zn2+ to P2O5=1:5 to 1.30.

Description

Aqueous solution and process for phosphating metallic surfaces

Description

The invention relates to an aqueous, phosphate-containing solution for producing phosphate layers on metallic surfaces made of iron, steel, zinc, zinc alloys, aluminum or aluminum alloys. The invention further relates to a method for phosphating metallic surfaces using an aqueous phosphating solution.

In the German patent application 196 34685.1 dated 28.08.1996 an aqueous, phosphate-containing solution for the production of phosphate layers on metallic surfaces made of iron, steel, zinc, zinc alloys, aluminum or aluminum alloys was proposed, which contains 0.3 to 5 g of Zn ²⁺ / l and Contains 0.1 to 3 g nitroguanidine / 1, the S value being 0.03 to 0.3 and the weight ratio Zn ²⁺ to P ₂ 0 ₅ = 1: 5 to 1:30, and which produces crystalline phosphate layers, in which the crystallites have a maximum edge length <15μm. In the German patent application, a process for phosphating was also proposed, in which the metallic surfaces were cleaned, then treated with the aforementioned aqueous, phosphate-containing solution for a period of 5 seconds to 10 minutes at a temperature of 15 to 70 ° C. and finally with water be rinsed. The invention has for its object to improve the aqueous, phosphate-containing solution and the method for phosphating, which were proposed in German patent application 196 34 685.1, so that the maximum edge length of the crystallites present in the phosphate layers produced is significantly <15 microns that the phosphate layers produced have a layer weight of 2 to 4 g / l and that the phosphate layers produced are constant or uniform with regard to the layer weight and the edge length of the crystallites even during a longer operating time of the phosphating bath.

The object on which the invention is based is achieved by creating an aqueous, phosphate-containing solution for producing phosphate layers on metallic surfaces made of iron, steel, zinc, zinc alloys, aluminum or aluminum alloys which contain 0.3 to 5 g of Zn / l, 0.1 contains up to 2 g nitroguanidine / l and 0.05 to 0.5 g hydroxylamine / 1, the S value being 0.03 to 0.3 and the weight ratio of Zn ²⁺ to P ₂ O _s = 1: 5 to 1 : 30 is. The essence of the invention is therefore that the solution proposed in the cited German patent application contains not only the accelerator nitroguanidine but also the accelerator hydroxylamine in a low concentration, the nitroguanidine concentration of the solution according to the invention compared to the nitroguanidine concentration proposed in the German patent application Solution was significantly lowered.

According to the invention, a solution which contains 0.1 to 1.5 g nitroguanidine / l and 0.1 to 0.4 g hydroxylamine / l is particularly advantageous and preferred. When using this preferred According to the features of the invention, optimal phosphating results are achieved.

Although EP-B 0 315 059, on the one hand, discloses a solution for phosphating iron surfaces, which has a zinc concentration of 0.2 to 2 g / 1 and which, as accelerators, contains hydroxylamine, hydroxylamine salts or hydroxylamine complexes contains, which give the solution a hydroxylamine concentration of 0.5 to 50 g / 1, preferably 1 to 10 g / 1, and although on the other hand from EP-B 0 633 950 a solution for the production of copper-containing phosphate layers on metal surfaces made of steel, galvanized steel, alloy-galvanized steel, aluminum and its alloys, which has a zinc concentration of 0.2 to 2 g / 1, a copper concentration of 0.5 to 25 mg / 1, a P ₂ 0 ₅ -Concentration of 5 to 30 g / 1, which contains hydroxylamine, hydroxylamine salts and hydroxylamine complexes as accelerators, which give the solution a hydroxylamine concentration of 0.5 to 5 g / 1, and which additionally serves as an oxidizing agent ganic nitro compound, it was extremely surprising to the person skilled in the art that even with comparatively low concentrations of nitroguanidine and hydroxylamine, phosphate layers can be produced which have an optimal layer weight of 2 to 4 g / m ² , the layer weight of which is very uniform even in continuous operation and whose crystallites in each case have a maximum edge length of <15 μm, although the edge length is generally significantly <10 μm. These surprisingly advantageous effects of the solution according to the invention are associated with a further advantageous effect, which consists in the fact that the solution according to the invention, because of the comparatively low concentration of the accelerators, has relatively low accelerators. Amounts from the phosphating bath in the subsequent treatment stages and ultimately in the wastewater. The solution according to the invention thus ensures that both accelerators of the phosphating are supplied almost quantitatively.

The solution according to the invention is also not disclosed or suggested to the person skilled in the art by the prior art cited above, because compared to the solution proposed in German patent application 196 34 685.1, the solution according to the invention only uses the lower nitroguanidine concentrations and additionally hydroxylamine and compared to the solutions which are known from the two European patents cited, the solution according to the invention uses hydroxylamine concentrations which are lower than the hydroxylamine concentrations disclosed in the cited prior art, wherein, in addition, the use of nitroguanidine as in both European patents cited Accelerator is not disclosed and that both European patents cited require the person skilled in the art to use high hydroxylamine concentrations, because according to the document EP-B 0 315 059 a hydroxylamine concentration of 1 b is 10 g / 1 as preferred and according to Example 1 of EP-B 0 633 950, a hydroxylamine concentration of 1.7 g / 1 is used. It is therefore to the merit of the present invention to have recognized that high-quality phosphate layers can be deposited on a variety of metallic surfaces from a solution which has a very low hydroxylamine content and a comparatively low nitroguanidine content Hydroxylamine content not that of the prior art outlined route, namely the use of quite high hydroxylamine concentrations.

In a further embodiment of the invention it is provided that the solution contains 0.3 to 3 g of Zn ²⁺ / l. The solution is therefore particularly suitable for use in the context of low-zinc technology. It is further provided in a further embodiment of the invention that the solution additionally contains 0.5 to 20 g / N0 ₃ ^" / l, that the solution additionally contains 0.01 to 3 g Mn ²⁺ / l and / or 0.01 to 3 g Ni ²⁺ / l and / or 1 to 100 mg Cu ²⁺ / l and / or 0.01 to 3 g Co ²⁺ / l. The copper content of 1 to 100 mg Cu ⁺ / 1 is responsible in particular for that high-quality phosphate layers are produced in the absence of nickel. When phosphating aluminum-containing surfaces, it has proven particularly useful according to the invention if the solution contains 0.01 to 3 g F ^" / l and / or 0.05 to 3.5 g / 1 contains at least one complex fluoride. According to the invention, the solution contains as complex fluoride (SiF _s ) ^{2 ~} or (BF ₄ ) W

The nitrate content according to the invention advantageously favors maintaining a constant layer weight. The nitrate is added to the phosphating solution in the form of alkali metal nitrates and / or by the cations present in the system, for example as zinc nitrate and / or as HN0 ₃ . Since the nitrate-free aqueous solution also delivers good phosphating results, the known acceleration effect of the nitrate is in most cases of minor importance in the present case. The metal ions Mn ⁺ , Ni ²⁺ , Cu ²⁺ and Co ⁺ added to the phosphating solution are built into the phosphate layer and improve paint adhesion and corrosion protection. The free fluoride is added to the phosphating solution if metallic ones consisting of aluminum or aluminum alloys 6

Surfaces are phosphated. The complex fluorides are added to the phosphating solution, especially to improve the phosphating result on galvanized surfaces.

The object underlying the invention is further achieved by the creation of a method for phosphating metallic surfaces, in which the metallic surfaces are cleaned, then with the aqueous, phosphate-containing phosphating solution for a period of 5 seconds to 10 minutes at a temperature of 15 to 70 ° C treated and finally rinsed with water. This process can be carried out using simple technical means and is extremely reliable. The phosphate layers produced by the process have a consistently good quality, which does not decrease even with a longer operating time of the phosphating bath. The minimum phosphating time in the process according to the invention is less than in known low-zinc processes which work with the usual accelerators. The minimum phosphating time is the time in which the surface is phosphated when closed. It has surprisingly been found that the process parameters which have proven advantageous in the process proposed in German patent application 196 34 685.1 can generally also be used in the process according to the invention.

According to the invention it is provided that the treatment of the metallic surfaces with the phosphating solution is carried out by spraying, dipping, splash-dipping or rolling. These working techniques open up a very broad and diverse range of applications for the method according to the invention. According to the invention, it has proven to be particularly advantageous if the phosphating solution used for spraying has a weight ratio of Zn ⁺ to P ₂ 0 ₅ = 1: 5 to 1:30, where the time required for spraying is 5 to 300 seconds, and if the phosphating solution used for dipping has a weight ratio of Zn ²⁺ to P ₂ 0 ₅ = 1: 5 to 1:18, the time required for dipping being 5 seconds to 10 minutes .

According to the invention, it is advantageous in many cases if the metallic surfaces are treated after cleaning with an activating agent which contains a titanium-containing phosphate. This supports the formation of a closed, crystalline phosphate layer. It is also provided according to the invention that the metallic surfaces are aftertreated with a passivating agent after the rinsing process following the phosphating. The passivating agents used can be both Cr-containing and Cr-free.

When cleaning the metallic surfaces according to the method according to the invention, both mechanical impurities and adhering greases are removed from the surface to be phosphated. The cleaning of the metallic surfaces belongs to the known state of the art and can advantageously be carried out with an aqueous alkaline cleaner. It is advisable to rinse the metal surfaces with water after cleaning. The cleaned or phosphated metal surfaces are rinsed either with tap water or with deionized water.

According to the invention, it is particularly advantageous if the nitroguanidine is introduced into the aqueous solution in the form of a stable, aqueous suspension. This can be done either in that the stable, aqueous suspension contains a layered silicate as stabilizer, the Layered Silicates [Mg _s (Si _7/4 Al _{0 / S} ) O ₂₀ (OH) ₄ ] Na _0/6 x XH ₂ 0 or [(Mg _{5 4} Li _{0 6} ) Si ₈ 0 ₂₀ (OH, F) ₄ ] Na _{0 6} x XH ₂ 0 in an amount of 10 to 30 g / 1 nitroguanidine suspension, or it can be done in that the stable, aqueous suspension contains a stabilizer consisting of a polymeric sugar and polyethylene glycol, the Weight ratio of the polymeric sugar to polyethylene glycol is 1: 1 to 1: 3 and the stabilizer is used in an amount of 5 to 20 g / 1 nitroguanidine suspension. With both stabilizers of the nitroguanidine suspension it is advantageously achieved that the suspension remains unchanged for several months and that the sludge separation in the phosphating bath is favored. The introduction of the nitroguanidine in the phosphating solution in the form of a stabilized suspension avoids the disadvantages which result from the fact that nitroguanidine is in the form of a powder and can only be distributed evenly in the phosphating solution in this form with difficulty. The suspensions produced according to the invention can be easily pumped and are stable over 12 months, which means that the nitroguanidine does not settle even after a long time. The suspensions are prepared by suspending the layered silicate or the organic stabilizer in deionized water and then stirring in the nitroguanidine.

At the pH of 2 to 4 in the phosphating solution, the suspension is destroyed and the nitroguanidine is released and dissolved in a fine distribution.

Finally, according to the invention it is provided that the solution according to the invention and the method according to the invention for the treatment of workpieces before painting, especially before electrocoating.

The subject matter of the invention is explained in more detail below, also using exemplary embodiments.

A) Definitions:

The Zn ²⁺ : P ₂ 0 ₅ ratio relates to the total P ₂ 0 ₅ . The determination of the total P ₂ 0 ₅ is based on the titration of the phosphoric acid and / or the primary phosphates from the equivalence point of the primary phosphate to the equivalence point of the secondary phosphate. The S value indicates the ratio of free acid, calculated as free P ₂ 0 ₅ , to total P ₂ 0 ₅ . The definitions and determination methods for the total -P ₂ 0 ₅ and the free P ₂ 0 ₅ are explained in detail in the publication by W. Rausch "The Phosphating of Metals", 1988, pages 289 to 304.

B) Process parameters:

The following comparative and exemplary embodiments were carried out using the following process steps: a) The surfaces of metallic objects made of sheet steel were cleaned with a weakly alkaline cleaner (2% strength aqueous solution) for 6 minutes at 60 ° C. and in particular degreased. b) This was followed by rinsing with tap water for 0.5 minutes at room temperature. c) This was followed by activation with a liquid activating agent which contained a titanium phosphate for 0.5 minutes at 50 ° C. d) It was then phosphated by dipping at about 55 ° C. for 3 minutes. e) Finally, it was rinsed with tap water for 0.5 minutes at room temperature. f) The phosphated surfaces were dried in the oven at 80 ° C for 10 minutes.

C) Concentrates for preparing the phosphating solution:

The concentrate I contains, with the exception of hydroxylamine and Cu ²⁺ , all inorganic components of the

Phosphating solution. Concentrate II consists of a stabilized nitroguanidine suspension. Concentrate III consists of an aqueous solution of hydroxylamine salts, hydroxylamine complexes or hydroxylamine. If a phosphating solution containing Cu ^{2 * is} required, a concentrated Cu ²⁺ solution is used as concentrate IV. If metallic surfaces made of aluminum or aluminum alloys are to be phosphated, a solution is used as concentrate V which contains free fluoride-forming compounds. The phosphating solution according to the invention is prepared by mixing the concentrates I to V required in each case with the simultaneous addition of water. If the phosphating bath is not used for a long time, the hydroxylamine is often partially decomposed. The resulting hydroxylamine losses are compensated for by adding concentrate III to the phosphating bath. Aqueous solutions of hydroxylamine salts, hydroxylamine complexes or of hydroxylamine are used in a known manner as the hydroxylamine source.

D) Execution and comparative examples:

In accordance with the process parameters given under B), two steel sheets of different quality (ZI and Z2) were galvanized on one side. The Phosphating bath had the respective composition specified in the table, the total-P ₂ 0 ₅ content g in all examples 12 P ₂ 0 _5/1 amounted, and wherein the following have in the table used symbols meaning:

FS = free acid GS = total acid

Zn = Zn ²⁺ , g / 1

NG = nitroguanidine, g / 1 HA = hydroxylamine, g / 1 Cu = Cu ²⁺ , mg / 1 Mn = Mn ²⁺ , g / 1

The phosphating according to Comparative Example 1 was carried out with the exclusion of accelerators. In comparative example 2, only the accelerator hydroxylamine was present, while in comparative example 3, only the accelerator nitroguanidine was used. Examples 4 to 9 were carried out in the presence of both accelerators, the concentration of both accelerators being in the range preferred according to the invention.

The table shows both the layer weights and the crystallite edge lengths which could be achieved when Examples 1 to 9 were carried out. These data show that in Comparative Example 1, which was carried out in the absence of the two accelerators according to the invention, a phosphate layer of insufficient quality resulted, since both the layer weight and the edge length of the crystallites of the phosphate layer are comparatively large. at 12 comparative examples 2 and 3 still tolerable layer weights and sufficiently small crystallite edge lengths were obtained, so that both phosphate layers can be regarded as quite useful. Exemplary embodiments 4 to 9 show that, according to the invention, both optimum layer weights and extraordinarily fine-crystalline phosphate layers could be produced. Examples 4 to 9 thus demonstrate that the invention can be used to produce phosphate layers of very high quality, specifically when using very low concentrations of nitroguanidine and hydroxylamine in the phosphating bath. Of course, the phosphate layers produced in accordance with Examples 1 to 9 were closed. The edge lengths of the crystallites given in the table were determined on the basis of electron microscopic images of the individual phosphate layers.

o so

Example phosphate bath - crystallite * .J 00 weight g / m edge length μm σx oo

No.FS GS Zn NG HA Cu Mn ZI Z2 ZI Z2 g / i g / i g / i mg / 1 g / i

1 2.3 25, 7 1.6 0 0 6 1.0 8.0 5.5 10-15> 15

2 2.4 25.7 1.6 0 0.20 6 1, 0 4.0 5.5 <10 <10

3 2.4 24.6 1.6 0.40 0 5 1.0 6.0 6.5 <10 <10

4 2.3 24.0 1.5 0.40 0.22 5 1.0 4.0 4.0 <5 <5

5 2.3 23.5 1.5 0.55 0.23 4 0.9 2.3 2.3 <5 <5

6 2.3 23, 1 1.4 0.75 0.23 3 0.9 2.8 2.5 <3 <3

7 2.3 21.0 1-2 0.67 0, 15 3 0.9 2.0 2.0 <3 <3

8 2.2 22.0 1.3 0.68 0, 18 3 0.9 2.0 2.3 <3 <3

13 n

9 2.2 22.4 1.2 0.63 0, 19 2 0, 9 2.2 2.4 <5 <3 *O

Ox

Claims

14 Patent claims

1. Aqueous, phosphate-containing solution for producing phosphate layers on metallic surfaces made of iron, steel, zinc, zinc alloys, aluminum or aluminum alloys, the 0.3 to 5 g Zn ⁺ / l, 0.1 to 2 g nitroguanidine / l and 0, Contains 05 to 0.5 g hydroxylamine / l, the S value being 0.03 to 0.3 and the weight ratio of Zn ²⁺ to P ₂ 0 ₅ = 1: 5 to 1:30.

2. Aqueous solution according to claim 1, which contains 0.1 to 1.5 g nitroguanidine / l.

3. Aqueous solution according to claims 1 to 2, which contains 0.1 to 0.4 g hydroxylamine / l.

4. Aqueous solution according to claims 1 to 3, which contains 0.3 to 3 g of Zn ²⁺ / l.

5. Aqueous solution according to claims 1 to 4, which contains 0.5 to 20 g N0 ₃ ^" / 1.

6. Aqueous solution according to claims 1 to 5, the 0.01 to 3 g of Mn ²⁺ / l and / or 0.01 to 3 g of Ni ²⁺ / l and / or 1 to 100 mg of Cu ²⁺ / l and / or contains 0.01 to 3 g of Co ²⁺ / l.

7. Aqueous solution according to claims 1 to 6, which contains 0.01 to 3 g F ^" / l and / or 0.05 to 3.5 g / 1 of at least one complex fluoride.

8. Aqueous solution according to claims 1 to 7, which contains as complex fluoride (SiF _s ) ^{2 ~} or (BF ₄ ) ^" .

9. A process for phosphating metallic surfaces, in which the metallic surfaces are cleaned, then treated with the aqueous, phosphate-containing solution according to claims 1 to 8 for a period of 5 seconds to 10 minutes at a temperature of 15 to 70 ° C and finally with Rinsed with water.

10. The method according to claim 9, wherein the treatment of the metallic surfaces with the phosphating solution is carried out by spraying, dipping, spray-dipping or rolling.

11. The method according to claims 9 to 10, wherein the phosphating solution used for spraying has a weight ratio of Zn ²⁺ to P ₂ 0 ₅ = 1: 5 to 1:30 and the time required for spraying is 5 to 300 seconds.

12. The method according to claims 9 to 10, wherein the phosphating solution used for dipping has a weight ratio of Zn ²⁺ to P ₂ 0 ₅ = 1: 5 to 1:18 and the time required for dipping is 5 seconds to 10 minutes.

13. The method according to claims 9 to 12, wherein the metallic surfaces are treated after cleaning with an activating agent containing a titanium-containing phosphate.

14. The method according to claims 9 to 13, in which the metallic surfaces are aftertreated with a passivating agent after the rinsing process following the phosphating. 16

15. The method according to claim 9, wherein the nitroguanidine is introduced into the aqueous solution in the form of a stable, aqueous suspension.

16. The method according to claim 15, wherein the stable, aqueous suspension contains a layered silicate as stabilizer.

17. The method according to claim 16, in which the layered silicates [Mg _β (Si ₇ , ₄ Al _{0 / S} ) O ₂₀ (OH) ₄ ] Na _{0 <s} x xH ₂ 0 or [(Mg _5.4 Li _{0 # β} ) Si ₈ 0 ₂₀ (OH, F) ₄ ] Na _{0> β} x XH ₂ 0 in an amount of 10 to 30 g / 1 nitroguanidine suspension.

18. The method of claim 15, wherein the stable, aqueous suspension contains a stabilizer consisting of a polymeric sugar and polyethylene glycol, wherein the weight ratio of the polymeric sugar to polyethylene glycol is 1: 1 to 1: 3 and wherein the stabilizer in an amount from 5 to 20 g / 1 nitroguanidine suspension is used.

19. Use of the aqueous phosphate-containing solution according to claims 1 to 8 and the method for phosphating according to claims 9 to 18 for the treatment of workpieces before painting.

20. Use according to claim 19 for the treatment of workpieces before electrocoating.