EP1394292A2 - Electrochemically produced TiO2 layers for providing corrosion protection or wash primers - Google Patents

Abstract

A layer of inorganic compound of a metal (A) is electrochemically-deposited onto the conductive surface from a solution of the metal (A); weight applied being 0.01-10 g/m2. The metal (A) is other than that forming the main component of the surface. The inorganic compound contains less than 20 wt% of phosphate ions. An Independent claim is included for a corresponding method of making an at least two-layer coating on an electrically-conductive surface. The second layer is added in a further stage, in which a coating of an organic polymer is applied. Preferred features: The deposited compound is an oxide. Deposition takes place at a potential relative to a standard hydrogen electrode of +/- 0.1V to +/- 300V; or a current density of +/- 0.1 - +/- 10000 mAcm-2. The inorganic compound is x-ray crystalline. In applying a second layer, a cathodically- or anodically- deposited electro-dip paint is applied. The process is a continuous sheet operation, the polymer layer being applied by dipping, spraying-on or using a coating roller. A powder paint is applied. Adhesive is applied. A corresponding metal component with double layer coating is also claimed.

Description

The invention is in the field of coating surfaces to these to protect against corrosion and / or to provide them with a primer for a subsequent organic coating. To do this, the Surfaces are electrically conductive, for example surfaces of metals or surfaces which have been made conductive by an appropriate treatment Represent glass or plastics.

A common technical task is metallic or not to provide metallic substrates with a first coating that has a corrosion-inhibiting effect and / or has a primer for an over it represents coating to be applied with organic polymers. For example metals are pretreated before painting. This is what technology stands for different procedures available. Examples include one layer-forming or non-layer-forming phosphating, a chromating or a chrome-free conversion treatment, for example with complex ones Fluorides from titanium, zirconium, boron or silicon. Technically easier to carry out, but a simple application of a primer coat is less effective a metal before painting it. An example of this is the application of Redlead. An alternative to the "wet" process is "dry" Procedures in which a corrosion protection or adhesive layer from a Gas phase is deposited. Such methods are for example as PVD or CVD process known. They can be electrical, for example through a Plasma discharge, be supported.

A layer produced or applied in this way can be used as serve as a corrosion protective primer for subsequent painting. The Layer can also be a primer for subsequent gluing represent. In particular metallic substrates, but also substrates made of Plastic or glass are often chemically or mechanically pretreated to ensure the adhesion of the adhesive to the substrate improve. For example, metal or Plastic parts in each case, but also glued together. Front and Today rear windows of vehicles are usually directly in the body glued. Further examples of the use of adhesive layers can be found in the production of rubber-metal composites. Here too the Metal substrates are usually mechanically or chemically pretreated before an adhesive layer is applied for gluing with rubber.

Bring the traditional wet or dry coating processes each with special disadvantages. Examples are chromating processes due to the toxic properties of chromium and the formation of highly toxic Sludges disadvantageous from an ecological and economic point of view. But chrome-free wet processes such as phosphating are also in generally associated with the formation of sludges containing heavy metals, the have to be disposed of at great expense. Another disadvantage of conventional wet Coating process is that the actual coating step often preparatory or follow-up steps are required. This increases the space required for the treatment line and the consumption of chemicals increases. For example, the one used almost exclusively in automotive engineering Phosphating with several cleaning steps, one activation step and usually associated with a post-passivation step. In all of these steps chemicals are consumed and waste to be disposed of.

While dry coating processes pose fewer waste problems, but have the disadvantage of a technically complex process (e.g. due to the requirement of vacuum) or are energetic consuming. High operating costs are mainly due to system costs and Conditional on energy consumption.

There is therefore a need for new coating processes for the manufacture of Corrosion protection or adhesive base layers, which are less expensive in terms of equipment as a dry process and the one compared to wet processes lower chemical consumption and lower waste volume get along.

That thin layers of metal compounds, such as oxide layers, be generated electrochemically on an electrically conductive surface is known in the art. For example, article Y. Zhou, J.A. Switzer: "Electrochemical Deposition and Microstructure of Copper (I) Oxide Films ", Scripta Materialia Vol. 38, No. 11, pages 1731-1738 (1998) electrochemical deposition and microstructure of copper (I) oxide films Stainless steel. The influence of the deposition conditions was particularly important investigated the morphology of the oxide layers. A practical application of the Layers do not emerge from this work.

The article M. Yoshimura, W. Suchanek, K-S. Han: "Recent developments in soft, solution processing: one step fabrication of functional double oxide films by hydrothermal-electrochemical methods ", J. Mater. Chem. Vol. 9, pages 77-82 (1999) examines the production of thin films of double oxides a combination of hydrothermal with electrochemical methods. A Application is seen in the manufacture of ceramic materials. The item contains no evidence of the usability of such layers as Corrosion protection and as a primer.

An electrochemical formation of an oxide layer also takes place with the as Known processes take place anodizing. The differs from this present invention in that on a substrate layers of Metal compounds are deposited, the metal being the metal compound is essentially a different metal than that which the possibly metallic surface.

It is also known to form crystalline zinc phosphate layers to support electrochemically. The disadvantages of phosphating (several Substeps such as activation, phosphating, post-passivation; Bout of Phosphating sludge) will not be overcome by this. The electrochemical support for the formation of zinc phosphate layers is not within the scope of the present invention.

In a first aspect, the invention relates to the use of a layer on an electrically conductive surface which can be obtained by, in step a), a layer of at least one inorganic compound of at least one metal A with a mass per unit area of 0.01 on this surface up to 10 g / m ^{2 is} electrochemically deposited from a solution which contains the metal A in dissolved form, the metal A being a different metal than the main component of the electrically conductive surface and the inorganic compound being less than 20% by weight Contains phosphate ions as a corrosion protection layer and / or as a primer for an organic coating.

The solution containing metal A in dissolved form is also referred to below as "Electrolyte" called. This represents water, dissolved in the salt of metal A. is, the conductivity of this solution for the purpose of the invention in the Usually sufficient. Should use a non-aqueous solvent or the conductivity of an aqueous solution is insufficient, a conductive salt such as a tetraalkylammonium halide. The Ions of the conductive salt are not or only to a minor extent in the Layer installed, but increase the electrical conductivity of the electrolyte.

The electrically conductive surface can be intrinsic act conductive surface such as a metallic surface. The However, layer can also be on a surface of an electrically little or not conductive material are deposited if the Surface is made electrically conductive. With plastics, for example done by first electrically chemical deposits conductive metal layer, which then forms the basis for the electrochemical Deposition of a compound of metal A. A glass surface can be made electrically conductive, for example, by using them with a Powdered an electrically conductive substance or a conductive layer through the gas phase, for example as a chemical Vapor Deposition (CVD). It is for the use according to the invention however preferred that the electrically conductive surface be a metal surface represents.

The inorganic compound of metal A is separated from a solution that contains the metal A in dissolved form. It can be a one- or multi-component aqueous or a non-aqueous solution act. Examples of non-aqueous solvents with a good one Solvent for suitable metal compounds are liquid ammonia, Dimethyl sulfoxide or organic phosphine derivatives. Examples of one multicomponent aqueous solution are water-alcohol mixtures.

The electrochemical deposition can be carried out cathodically or anodically, a cathodic deposition can be used more universally and is therefore preferred is. The deposition of the inorganic compound of at least one metal A from a corresponding solution can be done according to 2 different mechanisms respectively. On the one hand, the deposition can be coupled with a change in the Oxidation level of metal A, with a on the electrically conductive surface Layer of a poorly soluble compound of metal A in the opposite of the Solution changed oxidation level grows up. For example, Cathodic from an aqueous solution containing copper (II) ions, copper (I) oxide deposit. Another separation mechanism is based on the fact that the pH value through electrochemical processes on the electrically conductive surface shifts near the surface. As a result, the electrical conductive surface an inorganic compound of at least one metal A grow up that are hard on the surface under local pH conditions is soluble. It is not necessary that the oxidation state of the metal A changes during the deposition process. A shift in pH can take place on the electrically conductive surface, for example, in that Hydrogen ions are discharged and the pH value rises locally as a result.

If here the inorganic compound of at least one metal This means that this connection is definitely the metal A must contain. However, it can also contain other metals B, C, ... This other metals can be present in the solution in addition to metal A. and be deposited with it. These other metals can however, also be components of the electrically conductive surface and at Formation of the layer of an inorganic compound of at least one metal A. can be built directly into this connection. Examples of inorganic Compounds that contain another metal in addition to metal A. Mixed oxides, for example the structure type of the spinels or the Perovskite can belong. Examples include titanates and niobates.

Because of the easy feasibility and the ability to use water as a To use solvents, it is preferred that the in step a) deposited compound is an oxide. This can also be a mixed oxide different metals. However, the use according to the invention is not limited to oxides. It also includes non-oxide inorganic Compounds such as, for example, selenides, sulfides or nitrides suitable, possibly anhydrous, solvents can be separated.

It is not imperative in the sense of the invention that the inorganic Connection of at least one metal A is only binary or ternary Represents connection. Rather, this connection can also be set up in a more complex manner be, for example, ions or molecules from the solution into the compound can also be installed. Oxide hydrates or sulfates are an example of this.

The use according to the invention does not include a pure galvanization, since a plating layer is not an "inorganic compound" in the sense of this Represents invention. To the layer of at least one inorganic Connection of at least one metal A is rather the condition that at least part of the metal A is in an oxidation state> 0.

In principle, any layer can be used for the use according to the invention at least one inorganic compound of at least one metal A are used, which can be deposited electrochemically and which are sufficient is chemically stable to act as a corrosion protection layer. This means that the Layer with or without applied varnish better corrosion protection delivers as the uncoated metal surface. For the sake of price and Availability it is preferred that the metal A is selected from Mg, Ca, Sr, Ba, AI, Si, Sn, Pb, Sb, Bi, Ti, Zr, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, Zn, Cu. The for The most important metal for practical purposes are Al, Si, Ti, Zr, Mo, W, Mn, Fe, Co, Ni, Zn and Cu.

The electrochemical deposition can be potentiostatic or galvanostatic. The galvanostatic deposition is technically easier to carry out and is therefore preferred. The layer formation preferably takes place in that the inorganic compound on the electrically conductive surface at a potential compared to a standard hydrogen electrode between ± 0.1 and ± 300 V or a current density in the range of ± 0.1 to ± 10000 mA per cm ² electrically conductive surface is deposited. It is preferred to work at potentials between ± 0.1 and ± 100 V or at a current density in the range from ± 0.5 to ± 100 mA per cm ² . The signs in front of voltage and current density express that the deposition can be cathodic or anodic. Cathodic deposition, ie a negative potential compared to the standard hydrogen electrode, is preferred.

From the references cited at the beginning, it is known that the morphology, the chemical composition and the crystal structure of the deposited Layer depend on the deposition conditions and thus by choice of Conditions can be influenced. For example, the above are hanging Layer parameters from the concentration of the metal ions A and possibly further Components in the solution, the flow rate of the solution relative to the electrically conductive surface, the set potential and / or the set current density. The layer properties can thus be chosen specifically change this parameter. The deposition is carried out here preferably under conditions such that the inorganic compound deposits in X-ray crystalline form. X-ray crystalline means that the inorganic compound in a sharp X-ray diffraction experiment X-ray reflexes delivers. The resulting highly structured surface is particularly favorable as a primer for an organic coating.

Mixing of the electrolyte and / or a relative movement of the Electrolytes relative to the metallic conductive surface can form layers accelerate and influence the morphology of the layer. For example this is done by stirring the electrolyte or in the Pumped around electrolysis vessel. Furthermore, the electrolyte can be blown through a Gases, especially air, are mixed and moved.

Above was a deposition at a certain potential compared to a standard hydrogen electrode. Such Potential indication requires the use of a reference electrode, which is as close as possible to the electrically conductive substrate surface. At the practical operation, however, it is easier to work and the galvanostatic desired current density by varying the terminal voltage from electrical conductive surface as the working electrode and any counter electrode adjust. For example, counter electrodes are suitable, which are among the selected electrolysis conditions are stable for a sufficiently long time. examples are Stainless steel, gold, silver, platinum, graphite or glassy carbon

In a further aspect, the invention relates to a method for producing an at least two-layer coating on an electrically conductive surface, characterized in that
In a step a), a layer of at least one inorganic compound of at least one metal A with a mass per unit area of 0.01 to 10 g / m ^{2 is} electrochemically deposited on the electrically conductive surface from a solution which contains the metal A in dissolved form wherein the metal A represents a metal other than the main component of the electrically conductive surface and the inorganic compound contains less than 20% by weight of phosphate ions, and
in a subsequent step b) at least one layer of an organic polymer is applied to the layer deposited in step a).

Here, "an at least two-layer coating" means that the electrical conductive surface as described above a layer of at least an inorganic compound of at least one metal A and on this again at least one layer of an organic polymer is applied. Of course, the layer of an inorganic compound can also applied several different layers of organic polymers become. For example, this is known from automotive engineering, where according to previous state of the art on the as inorganic corrosion protection and Phosphate layer serving as adhesive layer generally at least 3 different Layers of organic polymers are applied. For example this can be layers of an electrocoat, a filler and a topcoat his.

It can be a layer of at least one inorganic compound at least one metal A is chosen to be a layer whose formation, Properties and composition described above.

In the process according to the invention for producing an at least two-layer coating, in one embodiment in sub-step b) a cathodically or anodically depositable electrodeposition paint can be applied. However, this presupposes that the electrical conductivity of the layer is large enough to deposit an electrodeposition paint. This is the case, for example, with a layer of copper (I) oxide with a mass per unit area of less than 10 g / m ² .

In this embodiment, the layer is deposited between the layers inorganic compound and the application of electrocoat preferably rinsed with water. This can be done by dipping or spraying respectively. It can be advantageous, at least in the last rinsing step rinse low-salt or deionized water. A chemical Post-passivation of the inorganic layer before the electrical one Dip painting, as is usually the case with phosphating, for example is not necessary in the method according to the invention.

In a further embodiment, the process according to the invention is carried out as Belt process through. In step b), an organic polymer layer is used applied by immersion or spraying or by application rollers. On Belt process implicitly requires a non-rigid substrate, so that this Process variant is preferably carried out on strips of metals. there the method is preferably carried out continuously. The electrochemical Layer formation in sub-step a) and the application of the organic The polymer layer in sub-step b) thus takes place with the belt running.

The application of an organic polymer layer to a running belt is known in the art as the "coil coating process". The coating systems used for this are also suitable for the method according to the invention. The organic polymer layer can have different thicknesses and different functions. For example, it can be only a few µm thick and serve as a shaping aid and / or as a primer for subsequent painting. The composition and layer thickness of the primer are preferably set so that electrical resistance welding is still possible. Furthermore, it should preferably be possible to apply an electrodeposable dip lacquer to the primer. Such organic primer layers on a chemically produced inorganic layer on a metal surface are known in the art under various trade names, depending on their function and composition. Examples include Durasteel ^R and Granocoat ^R.

While in the primer layers described above, the layer thickness in Range is below 10 microns and is, for example, 6 to 9 microns can in Coil coating processes also directly apply a thicker layer of organic paint applied, which will not be painted over later. The layer thicknesses are then in the range of 50 to 200 microns.

Furthermore, a powder coating can be used as the organic polymer in sub-step b) be applied. For this, the inorganic layer on the electrical conductive surface can no longer be electrically conductive to the extent that for Subsequent electrocoating is required. A powder paint is preferably applied to molded objects that are not strong exposed to corrosive loads. Examples of this are items such as Household appliances or electronic devices used in enclosed spaces be kept.

The organic layer applied in sub-step b) can also be an adhesive layer represent. The inorganic layer of at least one metal A serves then as an adhesive layer between the adhesive and the metallic conductive base. Especially for this embodiment of the method comes as metallic conductive pad not just a metal itself, but electrically conductive made surfaces of plastics or glass. Therefore the inorganic layer as an adhesive layer between one of the metal substrates, Plastic or glass and an adhesive act through the adhesive same or different substrates can be connected to each other. Examples can be found in the construction of vehicles, aircraft or household appliances, where metals are glued to each other or with plastic or glass. Also Bonding plastic with plastic is an option. In particular In this way, glass panes can be glued into vehicle bodies.

A special embodiment consists in that one in sub-step b) Apply adhesive with which a vulcanized or non-vulcanized rubber part is connected to a metal part. The resulting component becomes general referred to as "rubber-metal composite". It is usually done in such a way that a non-vulcanized rubber part with an adhesive over it as an adhesive layer serving inorganic layer connects to the metallic substrate and then by increasing the temperature, often with simultaneous exercise of pressure, vulcanized. These process steps are common in technology, however, the metallic substrate is not electrochemical with one layer an inorganic compound is coated, but either only is pretreated mechanically or wet-chemically.

Finally, in a further aspect, the invention relates to a metal component, the surface of which bears an at least two-layer coating that corresponds to a the ways described above is available. It can be for example vehicles or vehicle parts, household appliances, housings for trade electronic devices, furniture or architectural parts. Preferred materials for the metal components are iron, zinc, aluminum, magnesium and alloys, which consist of more than 50 atomic% of one of these elements. You can Metals and alloys are currently selected for the above Metal components are common.

In a preferred embodiment, the one described above bears Metal component, the inorganic compound of at least one metal A in X-ray crystalline Shape. X-ray crystalline means that the inorganic Connection in an X-ray diffraction experiment with sharp X-ray reflections supplies.

The advantages of the use according to the invention and that of the invention The method lies in the fact that thickness, composition and inner and outer structure of the inorganic layer by the choice of Deposition parameters are easier to control than with purely chemical ones Process management. Less will be needed to apply the layer Process stages are required than for phosphating and they generally fall less sludge than with a purely chemical layer formation. Compared The deposition process from the gas phase is electrochemical Separation faster and with less equipment and Energy consumption connected. Furthermore, it is not necessary as the Vapor deposition to provide volatile starting compounds.

Another advantage of electrochemical layer formation is that Layer growth over the electrical resistance on the metallic conductive Surface is controllable. Unless the growing layer has a higher one has electrical resistance than the electrically conductive surface - what in the The rule is the case - so the layer growth slows down when the electrical resistance becomes too high due to the layer formation. As long as it is there are still unoccupied areas of the metallic conductive surface or the layer is so thin that a current still flows at the set voltage the layer growth at these points. Is the metallic conductive surface almost completely covered with a layer of such a thickness that the electrical resistance increases significantly, the process of layer formation can be ended. With galvanostatically controlled layer growth it shows up the almost complete layer formation in that the terminal voltage rises sharply. The process can then automatically run at a preselected value the terminal voltage can be interrupted.

Ausführunasbeispiel Cathodic deposition of copper (I) oxide on steel from aqueous solution

Reinigung: schwach alkalisch (Ridoline^R 1559, 2.5 %, 75°C, 5-10 min.)

Spülung: Leitungswasser, entionisiertes Wasser

Aktivierung : KEINE

A pilot process for corrosion protection by means of cathodic deposition of Cu ₂ O was carried out on cold-rolled steel without an activation step (shortening the process chain). The following process parameters were set:

Cleaning: weakly alkaline (Ridoline ^R 1559, 2.5%, 75 ° C, 5-10 min.)

Rinse: tap water, deionized water

Activation: NONE

Conversion:

Electrolyte: 0.4 M CuSO ₄ + 3 M lactic acid, pH 10, 60 ° C, with 400 revolutions per minute stirring

Deposition both potentiostatic (0.2 V vs. standard hydrogen electrode) and galvanostatic (-0.8 to -2.6 mAcm ^-2 )

Treatment time: 10-300 seconds

Rinse : deionized water

Drying: compressed air

Characterization: scanning electron microscopy, X-ray photoelectron spectroscopy, Corrosion test (alternating climate test)

Painting: cathodic dip paint ED 5000

The layers formed are closed after a treatment time of approx. 50 s and consist of fine (<1 µm) crystallites of Cu ₂ O:

Due to the electrochemical nature of the process, the layer properties are very easy to control even without interfering with the electrolyte composition. For example, the layer thickness can be precisely controlled by the total charge when the total current is constant, e.g. for i = -800 mA: process time
(Seconds) layer weight
(gm ^-2 ) 10 0.4 30 0.7 60 1.1 120 2..4 300 5.6

Corrosion tests (10 cycles VDA alternating climate test, cathodic dip painting) show a significant improvement in corrosion protection through the coating depending on the applied layer thickness: process time
(Seconds) Alternating climate test: infiltration
U / 2 (mm) 10 4.8 30 4.5 60 3.9 120 3.6 300 2.6

Claims (13)

Use of a layer on an electrically conductive surface, which can be obtained in that on this surface in step a) a layer of at least one inorganic compound of titanium with a mass per unit area of 0.01 to 10 g / m ² from a solution, which contains titanium in dissolved form, is deposited electrochemically, titanium being a different metal than the main component of the electrically conductive surface and the inorganic compound containing less than 20% by weight of phosphate ions, as a corrosion protection layer and / or as an adhesive base for an organic coating , Use according to claim 1, characterized in that the compound deposited in step a) is an oxide. Use according to claim 1 or 2, characterized in that the inorganic compound on the electrically conductive surface at a potential compared to a standard hydrogen electrode between ± 0.1 and ± 300 V or a current density in the range of ± 0.1 to ± 10000 mA per cm ^{2 of} electrically conductive surface is deposited. Use according to one of the preceding claims, characterized in that the inorganic compound is X-ray crystalline. Method for producing an at least two-layer coating on an electrically conductive surface, characterized in that in step a) on the electrically conductive surface a layer of at least one inorganic compound of titanium with a mass per unit area of 0.01 to 10 g / m ² is electrochemically deposited from a solution which contains titanium in dissolved form, titanium being a metal other than the main component of the electrically conductive surface and the inorganic compound containing less than 20% by weight of phosphate ions, and in a subsequent step b) on the step a) deposited layer, at least one layer of an organic polymer is applied. A method according to claim 5, characterized in that the compound deposited in step a) is an oxide. A method according to claim 5 or 6, characterized in that the inorganic compound on the electrically conductive surface at a potential compared to a standard hydrogen electrode between ± 0.1 and ± 300 V or a current density in the range of ± 0.1 to ± 10000 mA per cm ^{2 of} electrically conductive surface is deposited. Method according to one of claims 5 to 7, characterized in that in sub-step b) a cathodically or anodically depositable electrodeposition lacquer is applied. Process according to one of claims 5 to 7, characterized in that the process is carried out as a belt process and in sub-step b) an organic polymer layer is applied by immersion or spraying or by application rollers. Method according to one of claims 5 to 7, characterized in that a powder coating is applied in sub-step b). Method according to one of claims 5 to 7, characterized in that an adhesive is applied in sub-step b). Metal component, the surface of which has an at least two-layer coating carries, which is obtainable according to one or more of claims 5 to 11. Metal part according to claim 12, characterized in that the inorganic compound of titanium is X-ray crystalline.