HUP0204415A2 - Dyed conversion layer - Google Patents

Abstract

The invention deals with a multi-layer coating comprising a single-conversion layer located on a metal and a color-effect layer located on said conversion layer; it also deals with its application. According to the invention, the conversion layer has pores and the second layer located on the conversion layer is obtained by applying a solution that contains at least one alkoxy-silane compound and a coloring agent that can be dissolved in a polar solvent; followed by polymerization and/or crosslinking of the applied azalkoxysilane compound. HE

Description

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Representative: Pintz and Partners Patent and Trademark Office, Budapest ··:♦ ♦·:· ...· ·..· ·..·

PUBLIC COPY

Colored conversion layer

The invention relates to a multilayer coating comprising a conversion layer arranged on a metal and a coloring layer disposed on this conversion layer; and to its use.

Conversion layers, which are arranged on metals, are generally known. Here and hereinafter the term “conversion layer” refers to a layer which is not formed by application to a metallic surface, but by chemical transformation of such a metallic surface and various components of an aqueous passivating electrolyte [Simon H. and Thoma M.; Angewandte Oberflächentechnik fiir metallisehe Werkstoffe, published by Carl Hanser Verlag, Munich (1985), Chapter 4]. Conversion layers have different functions, depending on the type of metal and the process used to form the conversion layer. For example, it can protect the metal from any chemical or mechanical influences, such as corrosion and wear.

In industry, the most well-known method for forming the conversion layer is the electrolytic formation of oxide layers on light metals, primarily aluminum, magnesium and titanium (such are described, for example, in the following patents: EP 0 333 048; DD 289 065, DE 41 24 730, DE 41 39 006, DE 196 80 596, DE 197 50 836, or DE 197 51 256), as well as the chromium plating, chromating or phosphatizing of ferrous metals.

In addition, it is known to color such conversion layers to produce decorative coatings.

Among such possibilities, one can mention the use of a passivating electrolyte which already contains a suitable coloring material.

This process is still very often used today, primarily for coloring anodized aluminum surfaces. The coloring agent used is most often a salt compound with a metal complex compound base, such as that described in German patent document DE 35 14 387 A1.

A significant disadvantage of this process is that, as the coloring material is embedded in the conversion layer, the chemical and mechanical properties of the layer deteriorate.

Another option, known in the literature, is to form a conversion layer, followed by coloring this conversion layer.

However, a significant problem is the insufficient abrasion resistance of the coloring layer on the conversion layer.

Attempts have long been made to improve this poor abrasion resistance, either by applying an additional protective layer to the colored conversion layer or by applying a colored protective layer to the uncolored conversion layer.

German patent DE 729 723, for example, describes the darkening of phosphate surfaces by applying a solution to a phosphated steel layer, the solution containing an organic coloring agent soluble in organic solvents as a colorant, further polyvinyl acetate and artificial shellac as a binder.

Furthermore, it is known from German patent document DE 800 200 to apply a protective layer by treating a magnesium object having a conversion layer with a coloring solution which also contains a resin or artificial resin dissolved in trichloroethylene or alcohol.

European patent document EP 0 488 280 describes a multilayer coating comprising a steel sheet as a metal substrate, a first zinc-containing layer applied to the steel surface, a second layer formed by chromium plating, and a third and final layer formed by thermal crosslinking of a non-aqueous solution, said non-aqueous solution comprising a polymer-based binder and a colorant.

However, tests have shown that in some cases the adhesion of the protective layer to a colored conversion layer is much weaker than to a comparable uncolored conversion layer. A possible explanation for this may be the effect of the coloring material acting as a “separating layer”.

The object of the invention is to provide a colored, multilayer coating on metals, considering that such coatings may not have their own intrinsic characteristics in terms of corrosion resistance and mechanical wear compared to a conventional uncolored conversion layer.

According to the invention, this object is achieved by a multilayer coating comprising at least two layers, wherein the first layer is a conversion layer arranged on a metal and having pores, and the second layer arranged on the conversion layer is obtained by applying a solution to the conversion layer, which solution comprises at least one alkoxysiloxane compound and a coloring agent, and the application is followed by polymerization and/or crosslinking of the alkoxysilane compound.

Two factors are decisive for the good adhesion of the layer according to the invention compared to the multilayer coatings known in the art. First, the conversion layer must have pores. Second, it is absolutely necessary that the layer containing the colorant has an alkoxysilane compound as a compound that can be polymerized and/or crosslinked.

This can only be ensured if the coloring layer arranged on the conversion layer is firstly connected to the surface of the conversion layer as a result of chemisorption through Si-O bonds, and secondly it is also connected within the pores by chemisorption.

As the alkoxysilane compound penetrates the pores, the contact surface and thus the chemisorption between the conversion layer and the polymer layer is significantly increased.

The size and frequency of pores in the conversion layer depends largely on the metal and the conversion process used.

Thus, for example, the pore size in a magnesium oxide layer produced according to the process described in European Patent Document EP 0 333 048 A1 is between 200 and 1000 nm; the pore size of an aluminum oxide layer (produced according to German Patent Document DE 41 39 006) is between 50 and 100 nm.

The selection of the coloring material is greatly influenced by the proper adhesion between the conversion layer and the polymer layer.

In one specific embodiment, the coloring agent is present in dissolved form in the solution containing at least one alkoxysiloxane compound; the coloring agent must be primarily soluble in tetraethoxysilane.

Thus, ^a homogeneous solution and consequently a homogeneous structure of the polymer layer is achieved. Therefore, no concentration of the coloring material occurs in the polymer layer, which could otherwise act as a “predetermined breaking point” between the conversion layer and the polymer layer. The solubility characteristics of the coloring material to be used according to the invention exclude the use of insoluble pigments (such as carbon black, titanium dioxide or iron oxide).

The polymer layer is then formed using polymerization methods that are generally known to those skilled in the art (e.g., air drying, heating, or UV irradiation).

The amounts of alkoxysilane compound and coloring agent in the solution to be used can vary widely. The solution generally contains 5-45% by weight, preferably 10-30% by weight of alkoxysilane compound and 2-15% by weight of coloring agent. Depending on the desired viscosity, the solution may also contain a polar solvent, which can be selected to ensure that the coloring agent dissolves and that the solvent does not react with the alkoxysilane compound (such as ethanol).

According to a particularly preferred embodiment of the invention, the alkoxysilane compound corresponds to the following general formula:

R'aR^bSÍX(4- _a -b) where in the formula • X represents an alkoxy, aryloxy or acyloxy group containing 1-12 carbon atoms, preferably 1-4 carbon atoms, and more preferably a methoxy, ethoxy, η-propoxy, isopropoxy, butoxy, phenoxy, acetoxy or propionyloxy group;

• R ¹ and R ² are independent of each other

- amino, monoalkylamino or dialkylamino group;

- an alkyl group, preferably an alkyl group having 1-6 carbon atoms, more preferably a methyl, ethyl, n-propyl, isopropyl, η-butyl, sec-butyl, tert-butyl, pentyl, hexyl or cyclohexyl group;

- an alkenyl group, preferably an alkenyl group having 2 to 6 carbon atoms, more preferably a vinyl, 1-propenyl, 2-propenyl or butenyl group;

- an alkynyl group, preferably an alkynyl group having 2 to 6 carbon atoms, more preferably an acetylenyl or propargyl group;

- an aryl group, preferably an aryl group having 6 to 10 carbon atoms, more preferably a phenyl or naphthenic group;

- an epoxy group, preferably an epoxy group having 3 to 16 carbon atoms, more preferably a glycidyl, glycidyl ether, glycidyl ester or glycidyloxyalkyl group; or

- a group X as described above; and • a and b are independently 0, 1, 2, or 3, where the sum of a and b cannot exceed 3.

A suitable alkoxysilane compound may be tetraalkoxysilane, epoxyalkoxysilane or aminoalkoxysilane.

Very good results are obtained when tetraethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane or 3-(aminoethylamino)propyltrimethoxysilane are used as the alkoxysilane compound.

To improve adhesion between the conversion layer and the polymer layer, it is also recommended to add a compound capable of forming a titanium complex with the solution to be applied to the conversion layer. The term “compound capable of forming a titanium complex” refers to compounds that form TiO ₂ - SiO ₂ systems, which form a bridge with the alkoxysilane compound and the conversion layer by complex bonding. As a result of the reaction, a further crosslinked polymer layer is obtained between the alkoxysilane compound and the titanium compound.

A particularly preferred compound is an alkoxytitanium compound, a titanic acid ester or a titanium chelate, more preferably a compound of the general formula Ti(OR)4, in which R is a C1-C6 alkyl group, preferably methyl, ethyl, η-propyl, isopropyl or butyl.

Very good results are achieved when tetraethoxy titanate with the formula Ti(OC ₂ H ₅ ) ₄ is used.

The molar ratio between the alkoxysilane compound and the titanium compound is not critical and is generally between 1 and 20.

Solutions containing both the alkoxysilane compound and the compound capable of forming a titanium complex are described, for example, in German patent document DE 41 38 218 A1 and can also be obtained from various companies (for example, the product under the brand name Deltacoll from the company Dörken).

A coloring agent which may be particularly suitable for use in the present invention is a metal complex coloring agent, such as that available from BASF under the name Neozapon, Ciha6

It is a product manufactured and marketed by Geigy under the name Orasol, by Sandoz under the name Savinyl, and by ICI under the name Lampronol.

In principle, any metal capable of forming a conversion layer can be used as the metal. However, light metals are particularly preferred, primarily aluminum and magnesium or alloys containing aluminum and/or magnesium, which are replacing steel and its alloys in many areas because of their lower relative density.

In terms of high wear resistance, conversion layers obtained by electrochemical processes are preferably used as conversion layers.

The invention further relates to the use of the solution for the production of the multilayer coating according to the invention, wherein such solution comprises at least one alkoxysilane compound as described above and a coloring agent which is soluble in a polar solvent.

The invention further relates to the use of the multilayer coating described above as a corrosion and wear-resistant protective coating for components used in automotive manufacturing, the electrical and electronic industry, mechanical engineering, aerospace technology, and as parts for sports equipment.

Claims (13)

PATENT CLAIMS 1. A chromate-free, multi-layer coating comprising at least two layers, characterized in that the first layer is a conversion layer arranged on the metal and having pores, and the second layer arranged on the conversion layer is formed by applying a solution to the conversion layer, said solution comprising: • at least one alkoxysilane compound; and • a coloring agent dissolved in said solution comprising at least one alkoxysilane compound, and by polymerizing and/or crosslinking said alkoxysilane compound after said application. 2. A chromate-free, multi-layer coating according to claim 1, characterized in that the coloring agent is soluble in tetraethoxysilane. 3. Chromate-free, multilayer coating according to claim 1 or 2, characterized in that the alkoxysilane compound complies with the R' is of _the formula R ² bSiX(4- _a .b), where in the formula • X represents an alkoxy, aryloxy or acyloxy group containing 1-12 carbon atoms, preferably 1-4 carbon atoms, and more preferably a methoxy, ethoxy, n-propoxy, isopropoxy, butoxy, phenoxy, acetoxy or propionyloxy group; • R ¹ and R ² are independent of each other - amino, monoalkylamino or dialkylamino group; - an alkyl group, preferably an alkyl group having 1-6 carbon atoms, more preferably a methyl, ethyl, η-propyl, isopropyl, η-butyl, sec-butyl, tert-butyl, pentyl, hexyl or cyclohexyl group; - an alkenyl group, preferably an alkenyl group having 2 to 6 carbon atoms, more preferably a vinyl, 1-propenyl, 2-propenyl or butenyl group; - an alkynyl group, preferably an alkynyl group having 2 to 6 carbon atoms, more preferably an acetylenyl or propargyl group; - an aryl group, preferably an aryl group having 6 to 10 carbon atoms, more preferably a phenyl or naphthenic group; - an epoxy group, preferably an epoxy group having 3 to 16 carbon atoms, more preferably a glycidyl, glycidyl ether, glycidyl ester or glycidyloxyalkyl group; or - a group X as described above; and • a and b are independently 0, 1, 2, or 3, where the sum of a and b cannot exceed 3. 4. The chromate-free, multilayer coating according to any one of claims 1-3, characterized in that the alkoxysilane compound is a tetraalkoxysilane, epoxyalkoxysilane or aminoalkoxysilane. 5. Chromate-free, multilayer coating according to any one of claims 1-4, characterized in that the alkoxysilane compound is tetraethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane or 3-(aminoethylamino)propyltrimethoxysilane. 6. The chromate-free, multilayer coating according to any one of claims 1-5, characterized in that the solution further contains a compound capable of forming a titanium complex. 7. Chromate-free, multilayer coating according to claim 6, characterized in that the compound capable of forming a titanium complex is an alkoxy titanium compound, a titanic acid ester or a titanium chelate, and preferably a compound of the general formula Ti(OR) ₄ , where in the formula R is an alkyl group having 1-6 carbon atoms, which is preferably a methyl-ethyl, n-propyl, isopropyl or butyl group. 8. Chromate-free, multilayer coating according to claim 7, characterized in that the compound capable of forming a titanium complex is tetraethoxy titanate of the formula Ti( _OC2H5 ) ₄ . 9. A chromate-free, multi-layer coating according to any one of claims 1-8, characterized in that the coloring material is a metal complex-based coloring material. 10. Chromate-free, multi-layer coating according to any one of claims 1-9, characterized in that the metal is a light metal, primarily aluminum, magnesium, or an alloy containing aluminum and/or magnesium. 11. The chromate-free, multilayer coating according to any one of claims 1-10, characterized in that the conversion layer is produced by an electrochemical process. 12. Use of a solution for preparing a chromate-free, multi-layer coating according to any one of claims 1-11, characterized in that the solution contains at least one alkoxysilane compound according to any one of claims 2-8 and a coloring agent which is soluble in a polar solvent. 13. Use of a chromate-free multilayer coating according to any one of claims 1-12, characterized in that it is used as a corrosion- and wear-resistant protective coating for components used in automotive manufacturing, electrical and electronic industries, mechanical engineering, aerospace, and sports equipment. The authorized person: