EP1509636A2

EP1509636A2 - Conversion layer for bases made of zinc or zinc alloys

Info

Publication number: EP1509636A2
Application number: EP03735311A
Authority: EP
Inventors: Hubert Otte; Ralf Feser
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-05-22
Filing date: 2003-05-19
Publication date: 2005-03-02
Also published as: AU2003236803A1; WO2003097900A2; AU2003236803A8; DE10223022A1; WO2003097900A3; US20060083942A1

Abstract

The aim of the invention is to create a novel conversion layer, the properties of which regarding breakability, decorative effect, and mechanical abrasion are at least not worse than those of previously known conversion layers. Said aim is achieved by providing the inventive conversion layer with at least one doped siliceous layer that is obtained by applying at least one alkaline siliceous solution which additionally contains aluminum ions and/or ions of at least one B-group element and/or ions of at least one lanthanide and/or ions thereof, which have been complexed with at least one complexing agent, and/or at least one organic polar compound. The novel conversion layer can be used as a corrosion-proof and abrasion-proof protective coating for technical parts and/or for decorative purposes.

Description

description

Conversion layer for substrates made of zinc or zinc alloys.

The present invention relates to a conversion layer for substrates consisting of zinc or zinc alloys, and the production and use thereof.

Zinc-containing or galvanized metallic surfaces tend to form corrosive white rust under the influence of moisture, which is not desirable. Known methods for preventing or reducing are the application of conversion layers with Cr (iπ) or Cr (VI) in an acidic medium, the reduction of Cr (VI) with alkali sulfite in alkaline alkali silicate solution (MacDermid JS500 and JS2000 methods) and the sealing with silicate coatings with or without admixtures of organic polymers. Furthermore, EP 0 749 501 describes a process which uses a combination of dissolved inorganic silicate, a dissolved inorganic aluminate and a silyl-containing crosslinking agent. Although Cr (VT) offers better protection than Cr (πi), the use of Cr (NI) is particularly disadvantageous due to its classification in cancer class 1. The EU end-of-life car order, which applies from July 1st, 2003, also makes the Amount of Cr (VI) per car limited to 2 grams. Because of these disadvantages, some automobile manufacturers want to do without Cr (VI) altogether. Cr (m) is classified as cancer class 2, but is accepted by industry as a replacement for Cr (VT). CrCDI) has the disadvantage, however, that when it is deposited from acidic media, known under the name Chromitierung® (DE 196 15 664 AI), the same corrosion-protecting properties as with Cr (VT) are not achieved. In addition, waste water contaminated with Cr (iπ) or Cr (VT), which is produced in the production of the conversion layers, generally represents a major problem. The known silicate coatings have the advantages of easy accessibility, the low price of their starting materials and the good quality Adhesion to metallic substrates. A disadvantage of the known silicate coatings, however, is their water vapor permeability, so that the substrates quickly corrode without additions of the coatings (for example: zinc dust, Mo-containing pigments). Another disadvantage is the relatively high proportion of silicate, which leads to brittleness in the layer thicknesses used leads. In order to at least reduce the brittleness in the known silicate coatings, organic, also water-suspendable, polymers are added to the coating solution or alkoxysilane compounds are used, as described in DE 100 14 035. The known silicate layers have a further disadvantage that a blue discoloration of the surface, for example in the case of "blue passivation", can occur. The process described in EP 0 749 501 has the disadvantage of the high toxicity of the silyl-containing crosslinking agents and the need for baking. Conversion layers are used not only for protection against corrosion, but also as a decorative coating, as described in DE 100 14 035. The natural post-patination of the zinc is also often used as a decorative effect, the known conversion layers being able to disadvantageously impede the natural post-patination or not to be visible.

The object of the present invention is to provide a conversion layer for substrates consisting of zinc or zinc alloys, this conversion layer should at least not have worse properties than the known conversion layers with regard to corrosion prevention, brittleness, the decorative effect and mechanical abrasion. This object is achieved according to the invention in that the conversion layer consists of at least one doped silicate layer which, by applying at least one silicate solution, additionally ions and / or ions complexed with at least one complexing agent from at least one subgroup element and / or from at least one lanthanide and / or contains aluminum and / or contains at least one organic polar compound. Further special features emerge from the subclaims. The conversion layer can be produced by applying the silicate solution by the known methods (for example by the immersion method, by rolling, by knife coating, by spraying, by spraying, etc.).

Examples of suitable silicate solutions are alkali water glasses and / or amino water glasses and / or organosiloxane-containing solutions, water being used as the solvent. Since the concentration to be used depends on the substrate to be coated and the additives used in the solution, the concentration and the type of Water glasses can be determined empirically by the person skilled in the art depending on the desired requirements without inventive intervention within the framework of the claimed teaching from the prior art. In a non-limiting manner and as the starting point for the empirical determination, the solution generally contains 1 to 10% by weight of the alkali / aqueous water glass.

Ions and / or ions complexed with a complexing agent of the subgroup elements (e.g. Fe, Cr, Mo, Ag, W, V, Ti, Y, Zr, Hf, etc.) and the lanthanides (e.g. La, Ce.) Are added to the silicate solution , Nd, Gd, Yb, etc.). Ions and / or ions of aluminum complexed with at least one complexing agent are also suitable as additives for the silicate solution. Since the concentration and form of the additive to be used depends on the substrate to be coated, the silicate solution, the other additives used in the solution, etc. and may also be limited by legal regulations, the concentration and form of an individual additive must also depend on the desired requirements can be determined empirically by the person skilled in the art without inventive intervention within the scope of the claimed teaching from the prior art. In a non-restrictive manner and as a starting point for the empirical determination, the ready-to-use solution contains approx. 0.01% by weight of the respective additive. The incorporation into the silicate solution can be carried out with the known methods, for example by stirring (as, for example, aqueous hydroxide suspension, form of a phosphate, complexed form, etc.) into a water glass solution, in the preparation of the water glass solution as a melt additive (eg in the form of a carbonate, etc. ) of water glass, etc.) happen. Organic silicate compounds and / or complexing agents (e.g. a mono-, di-, polycarboxylic acid, an organic amine, an organic phosphate, an organic phosphonate, an organic sulfonate, a hydrazone, a mercaptan, a stearate, etc .) suitable. These additives serve, for example, as wetting agents, solubility modifiers, inhibitors, etc. and can be introduced into the silicate solution using the known processes (for example by direct stirring, by addition as a complex compound with the other additives, in the preparation of the water glass solution as a melt additive in the water glass), etc.). It should be expressly pointed out that an organic polar compound can have several properties (for example wetting agents and complexing agents) and that the complexing agent can also have one can be inorganic compound. The concentration and form to be used, as for the other additives, must also be determined empirically for the individual case by the person skilled in the art for the same reasons, depending on the desired requirements without inventive step within the framework of the claimed teaching from the prior art. In a non-restrictive manner and as a starting point for the empirical determination, the ready-to-use solution generally contains about 0.01% by weight of organic compound / complexing agent.

The invention can be further developed within the scope of the claimed teaching so that two or more additives of the silicate solution can be added in combination. The addition of Ag and one of the other subgroup elements such as Ce may be mentioned as a non-limiting example. It should be expressly pointed out that the individual properties of the additives cannot behave additively and can influence one another, which the person skilled in the art can determine empirically in individual cases, depending on the desired requirements, without inventive step within the claimed teaching of the prior art can.

The advantages achieved by the invention are in particular that

the conversion layers produced can be very thin, with no flaking visible when a sheet coated therewith is buckled,

the conversion layers produced have no discoloration of the surface, e.g. with a "blue passivation",

- The anti-corrosion effect comes very close to and even exceeds the passivating effect of Cr (VI).

- the decorative effect of e.g. natural patination is retained,

- Waste water to be disposed of no longer arises, e.g. rinsing is unnecessary. The conversion layer according to the invention can be more resistant to corrosion and abrasion

Protective cover can be used for technical parts and / or for decorative purposes and is therefore of great economic interest.

The claimed teaching is now to be explained in more detail with the aid of a few examples. The concentrations given in the examples were empirically optimized by means of corrosion resistance according to DIN 50017 (40 ° C, 100% air humidity) and with the help of statistical methods. example 1

Use of Cr (HI): 0.1% (weight percent based on Cr (IÜ)) Cr (iπ) hydroxide, obtained from Cr (III) nitrate, was stirred into a water glass solution with a solids content of 36% by weight, whereby it dissolved. The concentrate thus obtained was diluted 1 + 9 with water and to a

Zinc surface applied.

In the corrosion test according to DIN 50017, coated parts showed 0% white rust after 12 days. On iron screws with galvanic Zn, ZnFe, ZnNi coating, the salt spray test in accordance with DIN 50021 showed service lives until the first appearance of

White rust of up to 600h for ZnNi, for Zn and ZnFe up to 260h.

Example 2

Use of Zr carbonate:

200 mg of Zr carbonate was dissolved in 2 ml of HNO ₃ , precipitated with KOH to pH 11, washed twice with H ₂ O and in each case centrifuged and 4 ml of H ₂ O added. 15 ml of potassium water glass with a solids content of 36% by weight were added. The concentrate thus obtained was diluted 1 + 4.4 with water and applied to a zinc surface.

In the corrosion test according to DIN 50017, coated parts showed 0% white rust after 12 days.

Example 3

Use of Ce (πi):

Ce (OH) _{3 was} precipitated from 50 mg of Ce ₂ (SO ₄ ) ₃ with KOH to pH 8, washed twice with H ₂ O and in each case centrifuged and 4 ml of H ₂ O added. 15 ml of potassium water glass with a solids content of 36% by weight were added. The concentrate thus obtained was diluted 1 + 4.4 with water and applied to a zinc surface. In the corrosion test according to DIN 50017, coated parts showed 0% white rust after 12 days.

Example 4

Use of Ce (IN):

50 mg Ce (SO ₄ ) ₂ , Ce (OH) _{4 was} precipitated with KOH to pH 8, washed twice with H ₂ O and centrifuged in each case and 4 ml H ₂ O were added. 15 ml of potassium water glass with 36% by weight solids content were added. The concentrate thus obtained was diluted 1 + 4.4 with water and applied to a zinc surface.

In the corrosion test according to DIΝ 50017, coated parts showed 0% white rust after 12 days.

Example 5

Use of phthalic acid:

200 mg of phthalic acid was successively mixed with 1 ml of ΝH ₃ (25%) and 4 ml of H ₂ O and 15 ml of water glass with a solids content of 36% by weight. The concentrate thus obtained was diluted 1 + 4.4 with water and applied to a zinc surface. In the corrosion test according to DIN 50017, coated parts showed <2% white rust content after 12 days.

Example 6

Use of adipic acid:

200 mg of adipic acid was successively mixed with 1 ml of NH ₃ (25%) and 4 ml of H ₂ O and 15 ml of water glass with a solids content of 36% by weight. The concentrate thus obtained was diluted 1 + 4.4 with water and applied to a zinc surface. In the corrosion test according to DIN 50017, coated parts showed <2% white rust content after 12 days. Example 7

Use of Fe (IH):

Hematite was stirred in water glass with a solids content of 36% by weight until the solution turned brownish. The concentrate thus obtained was decanted off and diluted 1 + 9 with water and applied to a zinc surface.

In the corrosion test according to DIN 50017, coated parts showed <4% white rust content after 12 days.

Example 8

Use of EDTA as complexing agents:

200 mg EDTA were brought to pH 10.5 with NH ₃ (25%) and made up to 20 ml with water glass with 36% by weight solids content. The concentrate thus obtained was diluted 1 + 9 with water and applied to a zinc surface.

In the corrosion test according to DIN 50017, coated parts showed <2% white rust content after 12 days.

Example 9

Use of urotropin:

400 mg urotropin were dissolved in 100 ml H ₂ O, 30 ml water glass with 36 wt .-% solids added and HO ad added 200 ml. The solution thus obtained was applied directly to a zinc surface. In the corrosion test according to DIN 50017, coated parts showed <2% white rust content after 12 days.

Example 10

Use of Ce (IV) + Ag: 50 mg Ce (SO) ₂ was precipitated with KOH ad pH 8, washed twice with H ₂ O and centrifuged in each case and 4 ml H ₂ O were added. 15 ml of potassium water glass with a solids content of 36% by weight were added. For this, 1 ppm Ag (as Ag (OH) ₂ ) is added. The concentrate thus obtained was diluted 1 + 4.4 with water and applied to a zinc surface.

Claims

Expectations

1. Conversion layer for substrates consisting of zinc or zinc-containing alloys, characterized in that the conversion layer consists of at least one doped silicate layer, which is applied by applying at least one silicate solution which additionally contains ions and / or ions complexed with at least one complexing agent by at least one Sub-group element and / or contains at least one lanthanide and / or aluminum and / or at least one organic polar compound is available.

2. Conversion layer according to claim 1, characterized in that the silicate solution is an alkali water glass and / or ammonium water glass.

3. Conversion layer according to claim 1, characterized in that the sub-group element is Fe, Co, Ni, Cr, Mo, Cu, Ag, W, V, Ti, Y, Zr or Hf.

4. Conversion layer according to claim 1, characterized in that the lanthanide is La, Ce, Nd, Gd or Yb.

5. Conversion layer according to claim 1, characterized in that the organic polar compound and / or the complexing agent is a mono-, di-, polycarboxylic acid, an organic hydroxycarboxylic acid, an organic polyhydroxycarboxylic acid, a glycol, an alcohol, an organic amine, an organic amino acid , an organic polyamino acid, an organic sulfonate, a hydrazone, a mercaptan, a stearate.

6. Use of a doped silicate solution for producing a conversion layer according to claim 1, characterized in that the solution contains at least one compound or element according to one of claims 1 to 5.

7. Use of a conversion layer according to one of claims 1 to 5 as a corrosion and / or abrasion-resistant protective coating for technical parts and / or for decorative purposes.