EP3126542A1

EP3126542A1 - Two-stage pre-treatment of aluminum comprising pickling and passivation

Info

Publication number: EP3126542A1
Application number: EP15712948.7A
Authority: EP
Inventors: Mathieu VAN DE CAPPELLE; Ina KRÜGERMANN; Thomas JOHN-SCHILLINGS; Andrea SOLDATI; Andreas Richard BENDER
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2014-04-03
Filing date: 2015-03-31
Publication date: 2017-02-08
Anticipated expiration: 2035-03-31
Also published as: TW201602414A; CN106232871B; MX2016012679A; US20170016119A1; ES2665193T3; PT3126542T; PL3126542T3; TWI665336B; US10415140B2; EP3126542B1; WO2015150387A1; DE102014206407A1; CN106232871A

Abstract

The invention relates to a method for anti-corrosion treatment of components produced from aluminum, comprising a pre-treatment stage and subsequent painting. The passivation of the pre-treatment stage includes the bringing of the components into contact with an acidic aqueous composition based on water soluble compounds of the elements Zr and/or Ti. Pickling and passivation are coordinated with each other such that a re-dosing of active components of the passivation solution can occur in substantial parts from the pickling solution.

Description

Two-stage pre-treatment of aluminum including pickle and passivation

The present invention relates to a process for the corrosion-protective treatment of aluminum-made components comprising a pretreatment stage and a subsequent coating. The passivation of the pretreatment stage involves contacting the components with an acidic aqueous composition based on water-soluble compounds of the elements Zr and / or Ti. Pickling and passivation are coordinated such that a subsequent addition of active components of the passivation solution to substantial parts from the Pickling solution can be done.

In the prior art, a variety of pre-treatment of aluminum-made components, in particular of strip materials, to mediate a

Corrosion protection and known as Lackhaftgrund based on acidic compositions. Usually, the aluminum surface is freed in a first step by the natural or caused by the manufacturing process oxide layer by pickling or pickling. The pickling not only involves the removal of the oxide layer, but typically includes pickling of the aluminum-made component itself to provide a homogeneous reproducible metallic surface for subsequent passivation. More recently, there has been a growing demand for pretreatments in the industrial mass production of components made of aluminum, in which the use of compounds of the element chromium can be completely dispensed with for improved environmental compatibility and sustainability.

The international publication WO 00/68458 A1 describes for the pretreatment of aluminum-made components suitable three-stage process consisting of acidic pickle, a sink and an acidic passivation based on the elements Zr and / or Ti, the sink between pickling and passivation preferably from more

Rinsing steps, within which the rinse water cascade against the

Transport direction of the component is performed.

Based on this prior art, the object of the present invention is now to optimize the pre-treatment stage for aluminum-made components in subsequent painting with respect to the procedural measures to maintain a satisfactory result of the pretreatment in the continuous operation of such a pretreatment stage and beyond the complexity of

Reduce pretreatment level. This object is achieved in a process for the corrosion-protective treatment of aluminum-made components comprising a pretreatment stage and a

subsequent painting achieved in that the component in the pretreatment stage first with an aqueous pickling solution having a pH of 1 to 3, a free acid content in points of at least 8 and a total fluoride content of at least 40 mmol / L, and then with an aqueous passivating solution, which has a pH of 1 to 3, a free acid content in points below 8 and a

Total fluoride content of less than 60 mmol / L, but at least 5 mmol / L and less than 10 mmol / L, but at least 0, 1 mmol / L of water-soluble compounds of the elements Zr and / or Ti based on the respective element is brought into contact, wherein in the pretreatment stage, immediately after contacting with the pickling solution, the contacting is carried out with the passivation solution.

Aluminum components made in accordance with the present invention

are treated corrosion-protective, are those whose surface formed of metallic substrates to at least 80%, preferably at least 90%, more preferably at least 95% surfaces of the substrate aluminum and / or its alloys, wherein alloys of the metal aluminum according to the invention more than 50 At .-% consist of the element aluminum. It is further preferred that the

Surface of the substrate aluminum contains no conversion layer with a coating weight of more than 10 mg / m2 based on such foreign elements whose component in the substrate aluminum is below 1 At .-%.

Suitable components made of aluminum in the method according to the invention are selected, for example, from semi-finished products such as sheet metal, strip, coil or wire or from complex three-dimensional production objects, which in turn are formed from strip material or sheets and / or are assembled or produced by die-casting.

In the context of the present invention, a pretreatment stage is a process stage separate from the application of the coating, comprising the pickling and passivation steps which are separated from each other with the aid of liquid compositions in the form of the pickling solution, the passivation solution, which are each stored independently in system tanks. In a preferred embodiment, the components made of aluminum are pretreated in series in the pretreatment stage of the process according to the invention. As pretreatment in series according to the invention Contacting a variety of aluminum-made components with the pickling and Passivierungslosung each stored in a system tank, without a complete after every pretreatment of a single aluminum-made component

Replacement with a new batch of pickling and passivation solutions stored in the system tanks of the pre-treatment stage.

The transition of the component from the stain to the passivation takes place "directly".

According to the invention, this means that the passivation of the pickle follows, without any wetting of the component with another liquid composition, the no

Passivierungslosung in the context of the present invention, is interposed. Moreover, in a preferred process according to the invention between pickling and passivation, no such process step takes place in which the provision and use of technical means is intended to dry or remove the aqueous liquid film adhering to the surface of the component, in particular by supplying thermal energy an air flow or by mechanical stripping of the liquid film. In a particularly preferred process according to the invention, the passivation immediately following the pickling is carried out "wet-on-wet", i.e. in such a way that a wet film adhering to the surface of the component of a liquid composition, which constitutes a pickling solution in the sense of the present invention, is included in the

Passivierungslosung the pretreatment stage is transferred.

In the method according to the invention is ensured in a continuous pretreatment of a series of aluminum-made components that in a resharpening of the stain by addition of acids and compounds which are a source of fluoride ions, in the immediately following passivation step essentially only water-soluble compounds of Elements Zr and / or Ti must be added. Only the transfer of active components from the pickling solution by the

inevitably adhering to the component wet film causes the same

Active components in the Passivierungslosung, which are both consumed there as well as being towed, at least partially replaced, without at the same time significant disadvantages in terms of the pretreatment result by the

Transfer of aluminum salts originating from the pickling process into the

Passivierungslosung result or be accepted. For effective utilization of the carryover to compensate for the consumed in the passivation active components, it is advantageous if the ratio of per minute pretreated surface of aluminum-made non-exhaustive components in square meters to vorratetem volume of Passivierungslosung in cubic meters at least 10, particularly preferred at least 50. Non-constituent components are characterized in that they do not transfer more than 1 liter of the pickling solution per square meter of the pickled component surface into the passivation solution, for example flat products such as strips, sheets or wires.

The free acid content in points is determined in the context of the present invention by diluting 10 ml of the pickling solution to 50 ml and titrating with 0.1 N sodium hydroxide solution to a pH of 3.6. The consumption of milliliters of caustic soda indicates the score.

In a preferred embodiment of the process according to the invention, the stain has a free acid content of at least 12 points, so that a pickling removal which is largely independent of the type of aluminum material to be treated and sufficient for the subsequent passivation is ensured, for example in US Pat

Series treatment of individual components made of different aluminum materials or in the series treatment of a mix of different

Aluminum materials manufactured individual components. Conversely, the free acid content in points should preferably not be greater than 16, in order to be able to keep the metal salt load in the pickling still at a moderate level with procedurally acceptable expense.

In addition to the setting of a free acid content in the pickling solution as a control parameter for the provision of optimally pickled in the process according to the invention surfaces of the components made of aluminum, the presence of a certain

Buffer capacity or a certain acidity for a stable process control in the series treatment exposed. For this purpose, the total acid content of importance and this is in the pickling solution of the method according to the invention preferably at least 15 points, but preferably not more than 20 points. Of the

Total acid content is inventively determined analogously to the free acid with the

Difference that is titrated up to a pH of 8.5.

The pickling solution preferably has a pH below 2.0 in a process according to the invention. Even then it is regularly ensured that a sufficient stain can take place in the pretreatment stage.

Regarding in the pickling solution of the pretreatment stage for the adjustment of

Acidic acid to be used has been found to be preferable to sulfuric acid. Accordingly, preference is given in the process according to the invention to the use of pickling solutions whose total acid content is formed in points of 80%, particularly preferably 90%, particularly preferably 95%, by means of sulfuric acid. A further prerequisite for a sufficient pickling effect of the components made of aluminum in the pickling solution of the pretreatment stage of the process according to the invention is the presence of fluorides which, as complexing agents for aluminum ions, on the one hand stain oxidic cover layers and, on the other hand, the high load of aluminum ions in the Stabilize pickling solution. Here it is preferred, if the

Total fluoride content in the pickling solution is at least 60 mmol / L. The total fluoride content is determined in the context of the present invention by means of a fluoride ion-sensitive electrode according to DIN 38 405-D-4-1.

Surprisingly, it has been found that the presence of layer-forming water-soluble compounds in the passivation of the elements Zr and / or Ti in the stain is not detrimental and therefore a simple possibility is given, the Passivierungslosung in the pretreatment step by the inventive method in which the

It is at best necessary to ensure that the active components of the passivation as constituents to be removed from the pickling solution in the pickle do not form a layer This would be disadvantageous for the subsequent passivation, in which the conversion layer formed under non-optimal layer formation conditions in the pickling solution is again partially dissolved and newly formed on the basis of the elements Zr and / or Ti and thus a less effective passivation of the components results It has been found that the pickling solution to meet this requirement profile in a preferred method according to the invention has to contain at least 7 mmol / L of water-soluble compounds of the elements Zr and / or Ti relative to the respective element to the debris for de n be able to make significant use of the replacement of the components of these components consumed in the passivation solution. On the other hand, the proportion of these

Components in the pickling solution do not exceed values for which a

Conversion layer formation based on the elements Zr and / or Ti is possible. In this respect, it is preferred according to the invention if no more than 30 mmol / L of water-soluble compounds of the elements Zr and / or Ti are contained in such pickling solutions, based on the respective element. In this connection, in order to avoid a partial layer formation based on the elements Zr and / or Ti in the stain it is furthermore preferred if the molar ratio of the total proportion of water-soluble compounds of the elements Zr and / or Ti relative to the respective elements to the total fluoride content in the

Pickling solution is less than 0, 1. In a preferred process according to the invention, the pickling solution additionally contains a surface-active organic compound, more preferably a nonionic surfactant, wherein the proportion of surface-active organic substances in the pickling solution is preferably at least 0.1 mmol / L. In this context, preference is generally given to those nonionic surfactants whose HLB value (hydrophilic-lipophilic balance) is at least 8, more preferably at least 10, particularly preferably at least 12, but is particularly preferably not more than 18, particularly preferably not more than 16. The HLB value is used to quantitatively classify nonionic surfactants according to their internal molecular structure, with a breakdown of the nonionic surfactant into a lipophilic and a hydrophilic group. The HLB value may take on the arbitrary scale values of zero to 20 and is calculated according to the present invention as follows:

HLB = 20- (1-M _L / M)

with M _L : molar mass of the nonionic surfactant lypophilic group

M: molecular weight of the nonionic surfactant

Particularly suitable nonionic surfactants are selected from alkoxylated alkyl alcohols, alkoxylated fatty amines and / or alkylpolyglycosides, more preferably from alkoxylated alkyl alcohols and / or alkoxylated fatty amines, particularly preferably from alkoxylated alkyl alcohols. The alkoxylated alkyl alcohols and / or alkoxylated fatty amines are preferably end-capped, particularly preferably having an alkyl group which in turn preferably has not more than 8 carbon atoms, more preferably not more than 4 carbon atoms.

The pickling solution in the present process is preferably set such that, for the wrought alloy EN AW 6060 (AIMgSiO, 5) at 40 ° C in an unstirred etching solution of the present process s ^"results in a pickling rate of at least 15 mgnr ² ^1, based on the element aluminum ,

In the passivation immediately following the pickle, a conversion layer based on the elements Zr and / or Ti is applied in the method according to the invention. For a sufficient passivation is preferred if after passivation a

Coating of at least 5 mg / m ² , preferably at least 10 mg / m ² , more preferably at least 20 mg / m ² , but preferably not more than 50 mg / ² determined by X-ray fluorescence analysis (RFA) results. For this purpose, it is further preferred that in the passivation solution of the method according to the invention at least 0.5 mmol / L, more preferably at least 1 mmol / L of water-soluble compounds of the elements Zr and / or Ti are contained based on the respective element. In this context, for an effective layer formation based on the elements Zr and / or Ti in the

Passivation is furthermore preferred if the molar ratio of the total proportion of water-soluble compounds of the elements Zr and / or Ti relative to the respective elements to the total fluoride content in the passivation solution is at least 0.1, more preferably at least 0.4.

In a preferred embodiment of the method according to the invention, the pH of the passivation solution in the pretreatment stage is at least 1.8, more preferably at least 2.0.

For a sufficient passivation in the pretreatment stage of the process according to the invention does not require the presence of water-soluble compounds of the

Elements chrome. In a further preferred embodiment of the method according to the invention, the passivation solution therefore contains a total of less than 10 ppm of water-soluble compounds of the element chromium calculated as Cr.

The application of the pickling and passivating solution stored in the respective system tanks of the pretreatment stage can be carried out using all methods known in the prior art, with immersion and spraying methods for contacting the components made of aluminum with these solutions being particularly preferred is the spray method as application mode.

The coating following the pretreatment stage according to the invention comprises the application of a composition containing a chemical or physical

hardening binder for forming a cover layer on the pretreated and made of aluminum component, wherein the coating layer resulting from the coating in the dried or cured state, a layer thickness of preferably at least one micrometer, more preferably of at least 10 μηη, measured according to

Wedge cutting method according to DIN 50986: 1979-03.

Suitable lacquers are autophoretic lacquers, electrodeposition lacquers, powder lacquers and liquid lacquers which can be applied by conventional means. With regard to the binders used according to the invention, both paints based on inorganic binders such as

For example, based on silicate or lime, as well as paints based on organic

Binders are used. According to the invention, the following application of lacquers based on organic binders, especially those which are particularly advantageous, is particularly advantageous contain less than 10 wt .-% of organic solvent constituents, the one

Boiling point below 150 ° C at 1 bar. In this context, therefore, powder coatings are preferred, in particular those with binders based on epoxy resins, carboxyl- and hydroxyl-containing polyester resins and / or acrylate resins, each having an excellent paint adhesion to the pretreated according to the invention made of aluminum components.

The component made of aluminum can be subjected after the pretreatment and before the painting of a sink, which serves to remove an adhering to the surface wet film of Passivierungslosung before the paint is applied. Furthermore, it is customary that the component is dried before the application of the paint. This is especially the case when a powder coating is to be applied.

Claims

Claims:

1 . Process for the corrosion-protective treatment of aluminum-made components comprising a pretreatment stage and a subsequent coating, wherein the component in the pretreatment stage first with an aqueous pickling solution, the pH of 1 to 3, a free acid content in points of at least 8 and a Total fluoride content of at least 40 mmol / L, and then with an aqueous Passivierungslosung, the pH of 1 to 3, a free acid content in points below 8 and a total fluoride content of less than 60 mmol / L, but has at least 5 mmol / L and less than 10 mmol / L, but at least 0.1 mmol / L of water-soluble compounds of the elements Zr and / or Ti based on the respective element contains, being brought into contact after in-contact -Bring with the pickling solution and before contacting with the Passivierungslosung no rinsing or drying step takes place.

2. The method according to claim 1, characterized in that the pickling solution has a free acid content in points of at least 12, but preferably not more than 16.

3. The method according to one or both of the preceding claims, characterized

characterized in that the pickling solution has a pH below 2.

4. The method according to one or more of the preceding claims, characterized

characterized in that the pickling solution has a total acid content in points of at least 15, but preferably not more than 20.

5. The method according to one or more of the preceding claims, characterized

characterized in that the pickling solution additionally contains at least 7 mmol / L, but preferably not more than 30 mmol of water-soluble compounds of the elements Zr and / or Ti based on the respective element.

6. The method according to claim 5, characterized in that the molar ratio of the total proportion of water-soluble compounds of the elements Zr and / or Ti based on the respective elements to the total fluoride content in the pickling solution is less than 0, 1.

7. The method according to one or more of the preceding claims, characterized in that 80%, preferably 90%, more preferably 95% of the points of the total acid of the pickling solution are formed by sulfuric acid.

8. The method according to one or more of the preceding claims, characterized

in that the pickling solution additionally contains a surface-active organic compound, preferably a nonionic surfactant, wherein the proportion of

surface-active organic substances is at least 0, 1 mmol / L.

9. The method according to one or more of the preceding claims, characterized

in that the component is brought into contact with the pickling solution and / or the passivation solution by spraying.

10. The method according to one or more of the preceding claims, characterized

characterized in that after the passivation and before painting a rinsing step is performed.

1 1. A method according to one or more of the preceding claims, characterized

characterized in that the component after the pretreatment stage and optionally after a rinsing step according to claim 10 is coated with a powder coating.