WO2001098557A1

WO2001098557A1 - Adhesion promoter in conversion solutions

Info

Publication number: WO2001098557A1
Application number: PCT/EP2001/006546
Authority: WO
Inventors: Bernd Schenzle; Heike Quellhorst; Alina Monica Koch
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 2000-06-21
Filing date: 2001-06-09
Publication date: 2001-12-27
Also published as: JP2004501280A; EP1292719A1; US20040020564A1; DE10030462A1; AU2001279651A1

Abstract

The invention relates to an aqueous solution for producing a conversion coating on metal surfaces. The solution has a pH value of 1.5 to 6 and contains complex fluorides of Ti, Zr, Hf, Si and/or B in quantities corresponding to a Ti, Zr, Hf, Si and/or B content of 20 to 500 mg/l; and 0.1 to 2 g/l adhesion-promoting coating additives. The composition of the aqueous solution is selected with the aim of ensuring that no crystalline zincous phosphate layer appears on the metallic surface. The coating additive preferably contains an element M selected from the following: B, Al, Si, Ti and Zr. At least one hydroxyl group and or one or more organic radicals is/are preferably bonded to said element. The organic radical or organic radicals R is/are chosen, independently of each other, from hydrocarbon radicals with 3 to 16 C-atoms or radicals (CH2)x-Y, x meaning a whole number from 1 to 10 and Y representing a hydroxyl group, a mercapto group, a primary or secondary amino group, a carboxyl group, an acrylic or methacrylic acid radical or an oxirane group or a molecule fragment containing one or more of the aforementioned groups or acid radicals, respectively.

Description

"Adhesion promoter in conversion solutions"

The invention is in the field of anti-corrosion treatment of metal surfaces on which a corrosion-protective conversion layer is produced. This conversion layer serves as a primer for subsequent painting.

There is an extensive state of the art for the deposition of corrosion protective layers on bare 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. As a rule, such a treatment is also suitable for zinc surfaces and possibly also for iron 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 chromium-free conversion treatment of aluminum surfaces with fluorides of boron, silicon, titanium or zirconium 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 polyacrylic acid or an ester thereof and b) 0.2 to 8 g / l of at least one of the compounds ^ ZrFg, ^ TiFg and

^ SiFg, where 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

^ SiFg, and c) a source of free fluoride ions that provides 17 to 120 g / l free fluoride.

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 ' ³ 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.

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 ^ 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.

It is known to add adhesion promoters to paints which improve the adhesion between the paint coating and the substrate. Lacquers differ from solutions for conversion treatment in that the lacquer layer adheres to the base due to sorption forces and no chemical reaction with the base occurs. In contrast, a conversion solution reacts chemically with the base, so that atoms from the base are built into the conversion layer.

The object of the invention is to improve the adhesion between a conversion layer and a lacquer layer applied thereon.

The invention relates to an aqueous solution for producing a conversion layer on metal surfaces, which has a pH in the range from 1.5 to 6 and the complex fluorides of Ti, Zr, Hf, Si and / or B in such an amount that the The content of Ti, Zr, Hf, Si and / or B is 20 to 500 mg / l, and contains 0.1 to 2 g / l of adhesion-promoting lacquer additives and the composition of the aqueous solution is chosen so that none on the metallic surface crystalline zinc-containing phosphate layer is formed. The aqueous solution preferably has a pH in the range from 2.5 to 4.5.

The complex fluorides of the elements mentioned can be introduced into the aqueous solution in the form of the corresponding fluoric acids or their alkali metal and / or ammonium salts. However, it is also possible to form the complex fluorides only in the aqueous solution itself by reacting hydrofluoric acid or fluorides with the ions of the metals mentioned. For example, complex fluorides of titanium or zircon are formed by the reaction of oxides or salts of these elements with hydrofluoric acid.

In addition to the complex fluorides, the aqueous solution can contain free fluoride, for example in the form of hydrofluoric acid or alkali metal or ammonium fluorides. For example, the free fluoride content can range from 0.001 to 1 g / l. This addition of free fluoride increases the pickling action of the aqueous solution and thus the rate of conversion layer formation, particularly in the case of hot-dip galvanized steel or aluminum.

The aqueous solution preferably contains the complex fluorides of Ti, Zr, Hf, Si and / or B in an amount such that the content of Ti, Zr, Hf, Si and / or B is 50 to 400 mg / l.

The adhesion-promoting paint additives are preferably selected from water-soluble compounds which contain at least one element M selected from the group B, Al, Si, Ti and Zr. The connections can be single or multi-core, in particular dual-core. In the case of bi- or polynuclear compounds, it is preferred that they contain different elements M in the molecule. Examples include compounds which contain both Al and Ti or both Al and Zr.

Compounds preferred as adhesion-promoting lacquer additives are those in which the element M has at least one hydroxyl group and one or more organic radicals R are bonded, the organic radical or the organic radicals R being selected independently of one another from hydrocarbon radicals having 3 to 16 carbon atoms or from radicals - (CH2) _X -Y, where x is an integer in the range from 1 to 10 and Y represents a hydroxyl group, a mercapto group, a primary or secondary amino group, a carboxyl group, an acrylic or methacrylic acid residue or an oxirane group or in each case a molecular fragment which contains one or more of the groups or acid residues mentioned.

The at least one hydroxyl group can already be bound to the element M when the compound is introduced into the aqueous solution to produce a conversion layer. However, it is also possible that the hydroxyl group bonded to the element M only forms by reaction of a precursor compound with water in the aqueous solution to produce a conversion layer. For example, one or more alcoholate groups can be bound to the element M and are replaced by OH groups by reaction with water.

Suitable organic radicals R are, in particular, those radicals which are known in silane chemistry as reactive groups for linking the silanes to components of paints and varnishes. Examples of such residues have been listed above. Several different organic radicals R can also be bound to the element M. The secondary amino group mentioned can be part of a diamine or polyamine unit, for example. For example, it can be part of an ethylenediamine or an ethylenediamine which is methyl-substituted at the terminal nitrogen atom. If, for example, Y is an ethylenediamine residue, this means that both a secondary and a primary amino group are present in the organic residue R. If Y is a carboxyl group, this is in general connected to the (CH ₂ ) χ chain via a C atom of the carboxyl group. In the special case of an acrylic or methacrylic acid residue, it is bound to the (CH ₂ ) _X chain via the carboxyl function itself, that is to say in an ester-like manner. As a result, the double bond of the acid residue is terminal and can therefore be copolymerized with paint components become. An oxirane group can form part of a glycidoxypropyl residue, for example.

Y can represent not only one of the above-mentioned groups as such, but also a molecular fragment containing several atoms, which contains one or more of the groups or acid residues listed above. For example, Y can mean a molecular fragment in which both a hydroxyl group and a carboxyl group are present. The glycidoxypropyl group already mentioned by way of example is a molecular fragment in which both a hydroxyl group and an oxirane unit occur.

In addition to the hydroxyl groups or their precursor fragments and the organic radicals R enumerated above, further groups or ligands which do not react chemically under the reaction conditions such as occur in the use according to the invention can be bound to the element M. For example, these can be alkyl radicals or carboxyl radicals. In particular, if the molecules of the adhesion-promoting coating additive are multinuclear, that is to say contain at least 2, possibly different, elements M, these are generally linked via ligands. These can be carboxyl groups, for example. However, hydroxyl groups or alcoholate groups can also perform such a bridging function.

In the context of the present invention, such adhesion-promoting coating additives are preferred which contain Al as element M or a combination of Al with one of the other elements M mentioned, in particular with Zr.

The aqueous solution preferably additionally contains 50 to 2000 mg / l, in particular 100 to 1000 mg / l, organic polymers. For example, the organic polymers can be selected from epoxy resins, aminoplast resins, tannins, phenol-formaldehyde resins, polycarboxylic acids, polymeric alcohols and / or their esterification products with polycarboxylic acids, poly-4-vinylphenol compounds, amino or copolymer compounds containing amino groups and polymers or copolymers of vinylpyrrolidone , The Use of such polymers in the field of

Metal surface treatment is known. For example, they are characterized in more detail in DE-A-100 10 758, whereupon more preferred for closer selection

Polymers is referenced.

Depending on the substrate, the aqueous solution can additionally contain 0.001 to 2, preferably 0.005 to 0.5 g / l ions of one or more of the metals Mn, Ce, Li, V, W, Mo, Mg, Zn, Co and Ni. These additional metal ions can further improve the corrosion protection effect and paint adhesion. For environmental reasons, however, attempts will be made to avoid using Co and Ni.

Furthermore, the aqueous solution may additionally contain 0.001 to 1.5, preferably 0.1 to 1 g / l phosphoric acid, phosphorous acid, phosphonic acid and / or their anions and / or their esters. Esters are to be chosen so that they are water-soluble or water-dispersible. These additives also improve corrosion protection and paint adhesion. However, according to the basic idea of the present invention, care should be taken not to choose such a combination of additives which leads to the formation of a crystalline zinc-containing phosphate layer. For example, this is achieved in that the treatment solution does not simultaneously contain zinc and / or manganese in concentrations of above 0.3 g / l and phosphoric acid or phosphate ions in concentrations of above 3 g / l.

However, it is advantageous if the aqueous solution further contains one or more components which are known in the technical field of phosphating as so-called phosphating accelerators. In phosphating, such accelerators have the main task of preventing the formation of bubbles of elemental hydrogen on the metal surface. This effect is also known as the depolarization effect. As with conventional phosphating, this also has the consequence in the solution according to the invention that the conversion layer is formed more quickly and that it is formed more uniformly. Accordingly, it is preferred that the aqueous solution select one or more phosphating accelerators 0.05 to 2 g / l m-nitrobenzenesulfonate ions, 0.1 to 10 g / l hydroxylamine in free or bound form, 0.05 to 2 g / l m-nitrobenzoate ions, 0.05 to 2 g / l p-nitrophenol .

1 to 70 mg / l hydrogen peroxide in free or bound form, 0.05 to 10 g / l organic N-oxides 0.1 to 3 g / l nitroguanidine 1 to 500 mg / l nitrite ions 0.5 to 5 g / l chlorate ions contains.

Since a particular object of the invention is to dispense with the use of toxic chromium compounds, it is preferred that the aqueous solution be free of chromium. Additions of chromium compounds to the aqueous solution could have a positive effect on the corrosion protection in individual cases, but corrosion protection and paint adhesion that can be achieved with the method according to the invention are sufficient even without the use of chromium compounds in the area of application concerned.

In principle, the aqueous solution, which contains the individual components in the application concentration for producing the conversion layer, can be prepared by dissolving the individual components in water in the desired application concentration at the place of use. In practice, however, one usually proceeds in such a way that a concentrate consisting of one or more containers is transported to the user, who prepares the ready-to-use solution from the concentrate or concentrates by dilution with water at the place of use. Accordingly, the invention comprises an aqueous concentrate present in one or more, in particular in two, containers, which after dilution with water by a factor between 50 and 500, in particular between 100 and 300, and if necessary adjusting the pH, an aqueous solution of the above described composition results. Whether you sell the concentrate in one or two containers depends in particular on whether it contains an organic polymer and whether this polymer is stable in the presence of the other components of the concentrate. If no organic polymer is present or if it is stable in the aqueous concentrate in the presence of the other constituents, the concentrate is preferably provided in a container. Certain organic

However, polymers such as polyacrylates are generally not stable in the presence of the inorganic components of the concentrate, but flocculate or lead to gel formation. In this case, it is preferable that

To divide the concentrate into at least two containers, one container preferably containing the complex fluorides and the other container preferably containing the organic polymers. The adhesion-promoting lacquer additives can either be added to the container with the complex fluorides or to the container with the organic polymers, the latter being preferred. The adhesion-promoting coating additives can, however, also be provided in a third container and only in the ready-to-use diluted solution of the other

Components are added.

Another aspect of the invention lies in a method for the corrosion protection treatment of metal surfaces, wherein the metal surfaces are brought into contact with an aqueous solution of the type described above for a period of between 0.5 and 5 minutes to produce a conversion layer.

The metal surfaces are preferably selected from those which are used in architecture, in mechanical engineering, in the furniture and household appliance industry and in shipbuilding, aircraft and vehicle construction. These are in particular surfaces of steel, of electrolytically or hot-dip galvanized or alloy-galvanized steel, as well as of zinc, aluminum and magnesium as well as alloys that consist of at least 50 atomic percent of iron, zinc, aluminum or magnesium.

The aqueous solution used in the process according to the invention preferably has a temperature between ambient temperature (about 15 to 20 ° C.) to about 70 ° C. The temperature range from 25 to 40 ° C. is preferred. The metal surfaces can be sprayed with the aqueous solution aqueous solution or by immersion in the aqueous solution and in the no-rinse process. In general, the aqueous solution is allowed to act on the metal surfaces for a period in the range from about 0.5 to about 5 minutes by spraying or dipping. A period in the range of 1 to 3 minutes is preferred for spray processes, and a period of 2 to 5 minutes is preferred for immersion processes. In the no-rinse process, the solutions are dried without intermediate rinsing about 3 to about 30 seconds after application to the metal surfaces.

In particular, automobile bodies or household appliances are often made from different materials. For example, steel and / or steels galvanized in different ways can be combined with one another or with components made of aluminum and / or magnesium or their alloys in each case. A particular strength of the method according to the invention is that an effective corrosion protection layer is also produced on the different materials in such cases. Accordingly, a special embodiment of the invention is characterized in that vehicle bodies or household appliances are treated which have surfaces made of at least 2 materials selected from zinc, aluminum, magnesium, alloys of these metals with one another or with other alloy components.

Usually the step of forming the conversion layer (= corrosion protection treatment) is followed by painting the metal surfaces with an electrodeposable dip or with a powder coating. Electrolytic dip coating, in particular cathodic dip coating, is preferred for vehicle bodies. Modern lead-free or low-lead cathodic electrodeposition lacquers are also suitable for this purpose, that is to say those immersion lacquers which contain less than 500 mg of lead per kg of dry substance in the lacquer suspension. Household appliances can also be dip-coated electrolytically. For cost reasons, however, powder coating is preferred. Furthermore, powder coating is often preferred in the architectural sector and in the furniture industry. So that's it The method according to the invention is preferably characterized in that the coating is carried out after the anti-corrosion treatment with an electrocoat or a powder coating.

The method according to the invention is usually embedded in the sequence cleaning, conversion protection treatment and painting. Between these process steps, one or more rinsing stages with process water, city water or fully demineralized water can be provided. Spraying or dipping processes can be used for the rinsing steps. The exemplary embodiments show a typical sequence of processes.

embodiments

Aluminum sheets of quality AA 6016 (AC 120) were used for the tests:

The test panels were subjected to the following procedure, with all the steps being carried out in the immersion process:

1.Clean with an alkaline cleaner from the applicant: Ridoline ^R 124 (2%) and Ridoline ^R 120 WX (0.1%) 55 ° C, 5 minutes,

2. Rinse with deionized water,

3. Rinse with deionized water,

4. Conversion layer formation by treatment with a test product according to Table 1 (pH 2.5, 30 ° C., 2.5 minutes),

5. drying by blowing with compressed air,

6. Application of TGlC-free polyethylene powder coating.

The following paint adhesion tests were carried out on the sheets pretreated in this way, the results of which are summarized in Table 2: 1. Cooking test: 2 hours in demineralized water at 100 ° C

2. Cross cut according to DIN EN ISO 2409

3. Cross cut with 5 mm deepening based on DIN EN ISO 2509 and DIN EN ISO 1520

4. Mandrel bending test according to DIN EN ISO 1519

Table 1: Test products

^a) commercial product from Chartwell International Inc., Attleboro Falls, MA 02763 (US): paint additive with M = AI + Zr, Y = -NH ₂ (according to claim 3) ^b) commercial product from Chartwell International Inc., Attleboro Falls, MA 02763 (US): paint additive with M = AI, Y = -NH ₂ (according to claim 3)

Table 2: Test results

Claims

claims

1. Aqueous solution for producing a conversion layer on metal surfaces, which has a pH in the range from 1.5 to 6 and the complex fluorides of Ti, Zr, Hf, Si and / or B in such an amount that the content of Ti, Zr, Hf, Si and / or B is 20 to 500 mg / l, and contains 0.1 to 2 g / l of adhesion-promoting lacquer additives and the composition of the aqueous solution is chosen so that no crystalline zinc-containing on the metallic surface Phosphate layer is formed.

2. Aqueous solution according to claim 1, characterized in that the adhesion-promoting paint additives are selected from water-soluble compounds which contain at least one element M selected from the group B, Al, Si, Ti and Zr.

3. Aqueous solution according to claim 2, characterized in that at least one hydroxyl group and one or more organic radicals R are bonded to the element M, the organic radical or the organic radicals R being selected independently of one another from hydrocarbon radicals with 3 to 16 C- Atoms or from residues - (CH2) _X -Y, where x is an integer in the range from 1 to 10 and Y is a hydroxyl group, a mercapto group, a primary or secondary amino group, a carboxyl group, an acrylic or methacrylic acid residue or an oxirane Group or each represents a molecular fragment containing one or more of the groups or acid residues mentioned.

4. Aqueous solution according to one or more of claims 1 to 3, characterized in that it additionally contains 50 to 2000 mg / l organic polymers.

5. Aqueous solution according to claim 4, characterized in that the organic polymers are selected from epoxy resins, aminoplast resins, tannins, phenol-formaldehyde resins, polycarboxylic acids, polymers Alcohols and / or their esterification products with polycarboxylic acids, poly-4-vinylphenol compounds, amino or copolymer compounds containing amino groups and polymers or copolymers of vinylpyrrolidone.

6. Aqueous concentrate in one or two containers, which after dilution with water by a factor between 50 and 500 and, if necessary, adjusting the pH, gives an aqueous solution according to one or more of claims 1 to 5.

7. A method for the corrosion protection treatment of metal surfaces, characterized in that the metal surfaces are brought into contact with an aqueous solution according to one or more of claims 1 to 5 for a period of between 0.5 and 5 minutes.

8. The method according to claim 7, characterized in that a painting is carried out after the anti-corrosion treatment.

9. The method according to claim 8, characterized in that the painting is carried out with an electrocoat or a powder coating.