WO2003002781A1

WO2003002781A1 - Corrosion protection agent and corrosion protection method for metal surfaces

Info

Publication number: WO2003002781A1
Application number: PCT/EP2002/006888
Authority: WO
Inventors: Heike Quellhorst; Alina Monica Koch; Patrick Droniou; Marian Pawlik
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 2001-06-30
Filing date: 2002-06-21
Publication date: 2003-01-09
Also published as: CA2453138A1; JP2004533542A; MXPA03011369A; US20040151619A1; EP1402083B1; ATE294259T1; CZ20033572A3; SK16192003A3; BR0210725A; CN1527889A; ES2240824T3; KR20040043135A; DE10131723A1; EP1402083A1; RU2004102694A; DE50202924D1

Abstract

The invention relates to an agent and method for carrying out the corrosion protection treatment of a metal surface. The invention is characterized in that the metal surface is brought into contact with a homopolymer or copolymer of vinyl pyrrolidone, whereby the application solution contains: a) 0.02 to 20 g/l phosphoric acid and/or at least one fluoro acid of one or more elements of the group Zr, Ti, Hf and Si or of each of their anions, and; b) 10 to 49.9 mg/l of a homopolymer or copolymer of vinyl pyrrolidone.

Description

"Corrosion protection agents and corrosion protection processes for metal surfaces"

The invention is in the field of anti-corrosion treatment of metal surfaces. One aspect of the invention is to deposit a corrosion-protective layer on the bare metal surface. A second aspect of the invention consists in enhancing the anti-corrosion effect of an anti-corrosion layer already deposited on the metal surface. A special feature of the invention is that no toxic heavy metals such as chromium or nickel have to be used.

There is extensive state of the art for the deposition of corrosion-protective layers on bare metal surfaces or the rinsing of already coated metal surfaces to increase the corrosion protection. The following are some examples of documents that deal in particular with the chrome-free treatment of aluminum surfaces. The term "conversion treatment" used here means that components of the treatment solution react chemically with the metal surface, thereby creating a corrosion protection layer in which both components of the treatment solution and metal atoms from the metal surface are incorporated.

The chrome-free conversion treatment of aluminum surfaces with fluorides of boron, silicon, titanium or zirconium alone or in combination with organic polymers is known in principle to achieve permanent corrosion protection and to create a basis for subsequent painting:

US-A-5 129 967 discloses treatment baths for a no-rinse treatment (referred to there as "dried in place conversion coating") containing aluminum a) 10 to 16 g / l polyacrylic acid or its homopolymers, b) 12 to 19 g / l hexafluorozirconic acid, c) 0.17 to 0.3 g / l hydrofluoric acid and d) up to 0.6 g / l hexafluorotitanic acid.

EP-B-8 942 discloses treatment solutions, preferably containing aluminum cans

a) 0.5 to 10 g / l of polyacrylic acid or an ester thereof and b) 0.2 to 8 g / l of at least one of the compounds H ^ ZrFß, F ^ TiF and l- ^ SiFg, the pH of the Solution is below 3.5,

and containing an aqueous concentrate for replenishing the treatment solution

a) 25 to 100 g / l polyacrylic acid or an ester thereof, b) 25 to 100 g / l of at least one of the compounds ^ ZrFg, ^ TiFg and

c) a source of free fluoride ions which provides 17 to 120 g / l of free fluoride.

DE-C-19 33 013 discloses treatment baths with a pH above 3.5 which, in addition to complex fluorides of boron, titanium or zirconium, in amounts of 0.1 to 15 g / l, based on the metals, additionally 0.5 up to 30 g / l of oxidizing agents, especially sodium metanitrobenzenesulfonate.

DE-C-24 33 704 describes treatment baths to increase paint adhesion and permanent corrosion protection to, among other things. Aluminum, which can contain 0.1 to 5 g / l polyacrylic acid or its salts or esters and 0.1 to 3.5 g / l ammonium fluorozirconate, calculated as Zrθ2. The pH values of this

Baths can fluctuate over a wide range. The best results are generally obtained when the pH is 6-8. US-A-4 992 116 describes treatment baths for the conversion treatment of aluminum with pH values between about 2.5 and 5, which contain at least three components:

a) phosphate ions in the concentration range between 1, 1x10 ^" ^ to 5.3x10 ^" ^ mol / l corresponding to 1 to 500 mg / l, b) 1, 1x10 ^"5 to 1, 3x10 ^" mol / l of a fluoric acid of an element from the group Zr , Ti, Hf and Si (depending on the element 1, 6 to 380 mg / l) and c) 0.26 to 20 g / l of a polyphenol compound, obtainable by reacting poly (vinylphenol) with aldehydes and organic amines.

A molar ratio between the fluoric acid and phosphate of about 2.5: 1 to about 1:10 must be observed.

DE-A-27 15 292 discloses treatment baths for the chromium-free pretreatment of aluminum cans which contain at least 10 ppm titanium and / or zirconium, between 10 and 1000 ppm phosphate and a sufficient amount of fluoride to form complex fluorides of the titanium and / or zirconium present however, contain 13 ppm and have pH values between 1, 5 and 4.

WO 92/07973 teaches a chromium-free treatment process for aluminum, which as essential components in acidic aqueous solution 0.01 to about 18 wt .-% H ₂ ZrF ₆ and 0.01 to about 10 wt .-% of a 3- (N- Cι _-4 alkyl-N-2-hydroxyethylaminomethyl) -4hydroxystyrene polymer used. Optional components are 0.05 to 10% by weight of dispersed SiO ₂ , 0.06 to 0.6% by weight of a solubilizer for the polymer and surfactant.

Despite this extensive state of the art, which is only reproduced here in excerpts, there is still a need for improved means and methods for the corrosion protection treatment of metal surfaces. The unpublished German patent application DE 100 05 113 is based on the knowledge that homopolymers or copolymers of vinylpyrrolidone have an excellent corrosion protection effect. In a first aspect, this invention relates to a method for the corrosion protection treatment of a metal surface, which is characterized in that the metal surface is brought into contact with a homo- or copolymer of vinylpyrrolidone. In a first embodiment of the invention, the metal surface can first be subjected to a conversion treatment according to the prior art, for example zinc or iron phosphating, a conversion treatment with fluoro acids of metals, for example titanium, zircon or hafnium or also of boron or silicon, or treatment with a solution or suspension of an organic polymer containing no vinyl pyrrolidone units. Examples of such polymers are mentioned in the literature cited at the beginning.

An alternative embodiment of the cited invention is that the metal surface is brought into contact with a homo- or copolymer of vinyl pyrrolidone while it is being subjected to a conversion treatment. In this case, a homo- or copolymer is therefore present in the treatment solution with which a conversion layer is generated on the metal surface. The treatment solution for producing the conversion layer can contain, for example, phosphoric acid or its anions. Furthermore, divalent cations such as zinc and / or manganese can be present in the treatment solution. A particular example of such a treatment solution for producing a conversion layer is a zinc phosphating solution which produces a crystalline layer of zinc-containing metal phosphates on the metal surface. However, the treatment solution can also contain phosphoric acid and / or its anions, but not divalent metals. An example of this is an iron phosphating solution which produces an essentially non-crystalline layer of metal phosphates and / or metal oxides on a metal surface, in particular an iron-containing surface. The presence of homo- or copolymers of vinylpyrrolidone in such a treatment solution improves the corrosion protection caused by the conversion layer is achieved. This also applies if the treatment solution contains, in addition to homopolymers or copolymers of vinylpyrrolidone, as the conversion layer-forming component, fluoric acids and / or complex fluorides of metals and semimetals, such as boron, silicon, titanium, zirconium and / or hafnium.

According to DE 100 05 113 cited above, the ready-to-use solution for the treatment of metal surfaces preferably contains between 0.05 and 200 g / l of a homo- or copolymer of vinylpyrrolidone. The object of the present invention is to improve the subject matter of DE 100 05 113 with regard to the efficiency of the use of chemicals.

The present invention relates to an agent for the treatment of metal surfaces which contains phosphoric acid and / or at least one fluoric acid of one or more elements from the group Zr, Ti, Hf and Si or in each case their anions and a homo- or copolymer of vinylpyrrolidone, characterized in that it is available as a ready-to-use solution containing a) 0.02 to 20 g / l phosphoric acid and / or at least one fluoro acid of one or more elements from the group Zr, Ti, Hf and Si or their respective anions and b) 10 to 49.9 mg / l of a homo- or copolymer of vinyl pyrrolidone contains.

In the presence of phosphoric acid, the agent for treating metal surfaces is a phosphating solution. If it does not contain ions of divalent metals such as zinc and / or manganese, it is present as a so-called "non-layer-forming" phosphating solution, for example in the form of an iron phosphating solution. Zinc and / or manganese Phosphating solutions containing, for example, 0.3 to 2 g / l of zinc ions and, if desired, additionally or instead of about the same concentration of manganese ions, are known in the conversion treatment field as so-called “layer-forming” phosphating solutions. Together with phosphoric acid or in its place, the treatment solution can also contain one or more fluoro acids of one or more elements from the group Zr, Ti, Hf and Si contain. Depending on the pH of the solution, both phosphoric acid and the above-mentioned fluoroacids are present in the form of one or more negatively charged anions. The ratio of acid anions to undissociated acid depends on the protolysis constant of the respective acid and on the pH currently set. This phenomenon is commonly known as acid-base balance. In addition to the essential components mentioned, the agents contain water and, if desired, further active ingredients or auxiliaries for adjusting the pH, for increasing the corrosion protection effect, for improving the applicability and possibly for other purposes.

If the agents according to the invention contain copolymers of vinyl pyrrolidone, these copolymers can contain one or more other monomers in addition to vinyl pyrrolidone. For example, they can be present as copolymers of 2 components or as copolymers of 3 components (= terpolymers). Mixtures of homo- and two-component copolymers, homo- and terpolymers or two-component copolymers and terpolymers can also be used.

The ready-to-use agent can be obtained by diluting a concentrate which is the subject of the unpublished German patent application DE 100 05 113. Depending on the specific composition, it may be the case that concentrates which already contain all the active ingredients are not stable in storage for a sufficiently long time. In these cases, it is preferable to divide the concentrates into at least two components, each containing selected components of the ready-to-use anti-corrosion agent. For example, it can be recommended that one component of the concentrate contains at least predominantly the inorganic components of the agent, while at least one other component of the concentrate contains the organic polymers. The two components of the concentrate can then have different pH values, as a result of which the storage stability of the concentrate components can be increased. To produce or refresh the agent in its application form, the individual components of the concentrate are included Diluted water so far that the active ingredients are in the desired concentration range. It may be necessary to adjust the pH to the desired range by adding an acid or a base.

Preferred concentration ranges for the active substances a) and b) in the application solution are: in the case of phosphoric acid or phosphate ions 5 to 20 g / l, in particular 8 to 16 g / l phosphate ions, in the case of fluoric acids such an amount that Zr, Ti , Hf and / or Si, based on these elements, are present in a concentration in the range between 20 and 1,000 mg / l, in particular 50 to 400 mg / l. The concentration of the polymers or copolymers of vinylpyrrolidone in the application solution is preferably in the range from 20 to 45 mg / l.

Suitable homopolymers or copolymers of vinylpyrrolidone are, for example, the polymers listed in Table 1 or the polymers of the monomers listed therein.

Table 1: Examples of homo- or copolymers of vinyl pyrrolidone

To increase the protection against corrosion, the agents according to the invention can contain further transition metal ions such as, for example, ions of the elements zinc, manganese, cerium or vanadium or also hydrofluoric acid or free fluorides. The presence of chromium or nickel ions can also offer advantages in principle. For reasons of work and environmental protection, however, the addition of chromium or nickel ions is preferably avoided. Accordingly, there is a preferred embodiment of the invention in that the agent is free of nickel and chromium. This means that these metals or their compounds are not intentionally added to the agent. However, it cannot be ruled out that ions of nickel and / or chromium may get into the agent (the treatment solution) in a low concentration from the container material or from the surfaces to be treated, such as steel alloys. However, in practice it is expected that the concentrations of nickel and / or chromium in the ready-to-use treatment solution will be no higher than about 10 ppm.

The ready-to-use agent according to the invention preferably has a pH in the range from 1 to 6 and in particular in the range from 2 to 5.5. This means that the fluoro acids of the elements Zr, Ti, Hf or Si, depending on the pH and protolysis constants, are partly in the form of the free acids, but partly in the form of their acid anions. It is therefore irrelevant whether these fluoro acids are used as such or in the form of their salts. Furthermore, acid-soluble compounds of Zr, Ti, Hf or Si as well as hydrofluoric acid or soluble fluorides can be added separately, since the fluoroanions of the elements mentioned form from this. Depending on the type of use, the pH must be adjusted to the desired range by adding acid such as the free fluoric acids of the elements mentioned, but also, for example, hydrofluoric acid, sulfuric acid, nitric acid or phosphoric acid or by adding a base such as alkali metal carbonate solution, alkali metal hydroxide solution or ammonia.

Because of the particularly good corrosion protection effect of homopolymers or copolymers of vinylpyrrolidone which contain caprolactam groups, the composition according to the invention contains, in a special embodiment, homopolymers or copolymers of vinylpyrrolidone which contain caprolactam groups.

Another aspect of the invention lies in a method for treating metal surfaces, wherein the metal surfaces, which if desired can already have an anti-corrosion layer, are brought into contact with the agent described above. The metal surfaces can, for example be selected from surfaces of steel, galvanized steel (electrolytically or hot-dip galvanized), alloy-galvanized steel, aluminum or magnesium. The metals aluminum and magnesium are usually not in pure form, but as alloys with other elements such as lithium, zinc, copper, silicon, magnesium (in the case of aluminum alloys) or aluminum (in the case of magnesium alloys). In particular, the method is designed for the treatment of surfaces of such metals, which are used in vehicle construction, in the household appliance industry, in the architecture or furnishing sector.

Metal surfaces that do not yet have a corrosion protection layer can be treated. The treatment method according to the invention then produces a corrosion-protective coating which at the same time improves the adhesion of an organic coating, such as a varnish, which may be applied later. However, metal surfaces which already have a pre-formed corrosion protection layer can also be treated with the method according to the invention. In this case, the corrosion protection effect of this already applied corrosion protection layer is further improved. For example, the method according to the invention is suitable for the aftertreatment of metal surfaces which have an X-ray amorphous or crystalline coating, as are produced, for example, by non-layer-forming or layer-forming phosphating, for example layer-forming zinc phosphating. The treatment according to the invention of such pretreated metal surfaces leads to the fact that pores remaining in the pretreatment are closed in the first corrosion protection layer.

In the treatment method according to the invention, the metal surfaces can be brought into contact with the treatment solution, for example by spraying or immersion. In this case, provision is preferably made for the treatment solution to be rinsed off with water after an exposure time which can be, for example, between 30 seconds and 5 minutes. Alternatively, the treatment solution with the metal surface in the so-called No-rinse process can be brought into contact. The treatment solution is either sprayed onto the metal surface or transferred onto the surface by application rollers. This is followed by drying of the treatment solution without further intermediate rinsing, after an exposure time which can be, for example, in the range from 2 to 20 seconds. This can be done, for example, in a heated oven.

For the treatment method according to the invention, the treatment solution preferably has a pH in the range from 1 to 6, with narrower pH ranges being preferred depending on the substrate and type of application and duration of action. For example, for the treatment of bare metal surfaces, the pH is preferably set to the range from 2 to 6, and in the case of treatment of aluminum surfaces in particular to the range from 2 to 4; when treating steel, zinc or galvanized steel, in particular in the range from 3 to 5. Metal surfaces which have already been pretreated and which carry a phosphate layer, for example, are preferably brought into contact with a treatment solution with a pH in the range from 3.5 to 5. The temperature of the treatment solution when carrying out the method according to the invention can generally be between the freezing point and the boiling point of the treatment solution, with temperatures in the region of room temperature or above being preferred for practical reasons. For example, the treatment solution can have a temperature in the range from 15 to 60 ° C. and in particular from 20 to 45 ° C.

The treatment method according to the invention represents a partial step in a sequence of method steps that is otherwise customary in the area concerned. For example, the metal surfaces to be treated are usually cleaned with a conventional cleaning solution before the treatment according to the invention. However, the cleaning step can be omitted if the metal surfaces to be treated were coated, for example galvanized, immediately before the treatment according to the invention, or if they were subjected to a conversion treatment, for example phosphating. After the treatment step according to the invention, the metal surfaces usually provided with an organic coating, for example a lacquer. This can be, for example, a powder coating or an electrolytically, in particular cathodically, immersible coating.

A sequence of processes which is particularly preferred when using the process according to the invention is that the metal surface is treated with an aqueous solution of an acid before it is brought into contact with the agent described above to produce a conversion layer, that is to say during a conversion treatment. The preceding process step of treating the metal surface with an aqueous solution of an acid before the conversion treatment is also referred to in the art as "acid pickling" or "pickling passivation". In the context of the sequence of processes according to the invention, acids can be used for this purpose, which are usually used for acidic pickling or pickling passivation. An example of this is phosphoric acid.

Examples of use: Use as conversion treatment

Example 1: Conversion process with previous pickling passivation

Substrates: Hot-dip galvanized steel (HDG), electrolytically galvanized steel (EG), aluminum (AC120), cold-rolled steel (CRS)

Process sequence (spray application):

1. Cleaning: Ridoline ^R 1570, 3%; 82 seconds, 55 ° C

Ridosol ^R 1270, 0.3% (commercial metal cleaner of the

applicant)

2. Rinse deionized water

3. Pickling passivation: phosphoric acid, 0.23%, 82 seconds 4. Rinse deionized water

5. Conversion treatment: 108 seconds; 30 ° C, containing an aqueous solution

H ₂ ZrF ₆ acid (45%; 1.38 g / l)

Vinyl pyrrolidone / vinyl caprolactam polymer (37 mg / l solid)

6. Rinse deionized water

7. Drying: compressed air

8. Painting: lead-free cathodic dip coating (BASF CG 310), coating thickness 20-23 μm

Example 2: Process sequence as above but without steps 3 and 4.

Corrosion test:

Zinc-coated substrates: paint adhesion after salt water storage

Aluminum copper accelerated salt spray test CASS DIN 50021,

10 days steel salt spray test SS DIN 50021, 21 days

Results: Infiltration at the Ritz (half the width of the Ritz): U / 2 in mm; Results of the stone chip test for paint adhesion (K value, K = 1: best paint adhesion, K = 10: worst paint adhesion))

Example 3: Conversion process with subsequent powder coating (galvanized steels) with copolymer mixtures

Substrates: CRS, EG, HDG process sequence (immersion application):

1. Cleaning: Ridoline ^R 1570, 2%; Ridosol ^R 1237, 0.3%; 5 minutes;

55 ° C (commercial metal cleaner of the applicant)

2. Rinse deionized water

3. Conversion treatment: 180 seconds; 30 ° C, with one of the following

Bath mixtures H ₂ ZrF ₆ acid (45%; 1.38 g / l) vinyl pyrrolidone / vinyl caprolactam copolymer (= P _a ) + vinyl pyrrolidone / vinyl imidazole copolymer (= P _b ) (37 mg / l solids content)

4. Rinse deionized water

5. Drying: compressed air

6. Painting polyester PES 5807 / RAL 5009 GL (TIGC-free), Herberts); approx. 60-80 μm

Corrosion test:

Neutral salt spray test DIN 50021 SS, 21 days

Results: Paint infiltration at the Ritz, half the width of the Ritz; Paint adhesion according to the cross cut test

The polymer ratios can be varied, for example, between homo- and / or copolymers P _a % = 100% -P _b % with P _a > 0. Example 4: Conversion Process with Copolymer Mixtures (Powder Coating)

Substrate: CRS

Process sequence (diving application):

1. Cleaning: Ridoline 1570, 2%; Ridosol 1237, 0.3%;

5 minutes, 55 ° C

2. Rinse demineralized water

3. conversion treatment 180 s; 30 ° C with one of the bath mixtures according to the following table H ₂ ZrF ₆ acid (45%; 1.38 g / l) + vinylpyrrolidone / vinylcaprolactam copolymer

Vinylpyrrolidone / vinylimidazole copolymer (= P _a ) (22 mg / l solids content)

4. Rinse deionized water

5. Drying: compressed air

6. Painting: polyester PES 5807 / RAL 5009 GL (TIGC-free), Herberts company; approx. 60-80 μm

Corrosion test:

Neutral salt spray test DIN 50021 SS, 21 days

Claims

claims

1. Agent for the treatment of metal surfaces which contains phosphoric acid and / or at least one fluoric acid of one or more elements from the group Zr, Ti, Hf and Si or their respective anions and a homo- or copolymer of vinylpyrrolidone, characterized in that it is ready for use Application solution is present which a) 0.02 to 20 g / l phosphoric acid and / or at least one fluoro acid of one or more elements from the group Zr, Ti, Hf and Si or their respective anions and b) 10 to 49.9 mg / l one Contains homo- or copolymers of vinyl pyrrolidone.

2. Composition according to claim 1, characterized in that it is free of nickel and chromium.

3. Composition according to one or both of claims 1 and 2, characterized in that the homo- or copolymer of vinylpyrrolidone contains caprolactam groups.

4. A method for treating metal surfaces, characterized in that the metal surfaces are brought into contact with an agent according to one or more of claims 1 to 3 while they are being subjected to a conversion treatment.

5. The method according to claim 4, characterized in that the metal surface is treated with an aqueous solution of an acid before it is brought into contact with an agent according to one or more of claims 1 to 3.

6. A method of treating metal surfaces, characterized in that the metal surfaces are brought into contact with an agent according to one or more of claims 1 to 3 after they have been Have undergone conversion treatment.