DE10305449A1 - Reaction solution for producing colored passivation film on zinc and its alloys, e.g. on iron or steel, is based on aqueous acid solution containing trivalent chromium ions and contains quinoline dye, preferably quinoline yellow - Google Patents

Abstract

Reaction solution for passivation of zinc (Zn) and its alloys, consisting of an aqueous acid reaction solution (I) with trivalent chromium ions, Cr(III), also contains quinoline dye(s) (II). Independent claims are also included for: (1) process for passivating Zn (alloys) based on (I), with addition of (II); (2) passivation film for Zn (alloys), which is as free as possible from Cr(VI), is colored by using a passivation solution with added (II) and provides corrosion protection of not less than 50 hours in the salt spray cabinet to DIN 50021 SS.

Description

The invention relates to a mixture of substances and a method for producing colored passivation layers, which are each based on the combination of a chromium (III) ion reaction solution based on a quinoline dye. In particular, the Invention to produce yellow, largely chromium (VI) -free passivation layers on zinc and its alloys.

Metallic materials, in particular Iron and steel, are galvanized and cadded to prevent them from being corrosive environmental influences to protect. The corrosion protection of the zinc is based on the fact that it is less noble than the base metal is and initially in its place is corroded. The base metal of the galvanized The component remains intact as long as it is continuous Zinc layer is covered.

The corrosive attack on the zinc layer in turn, chromate application can be delayed considerably. The corrosion protection provided by the zinc / chromate coating system is significantly higher than just through an equally thick layer of zinc. Furthermore, by a Chromating also affects the optical impairment of a component environmental influences delayed become. Furthermore, the visual appearance of the treated Components varied by the mostly colored chromate layers and be improved.

The benefits of being angry Chromating are so great that galvanic galvanized surfaces predominantly be chromated. In the prior art there are four main Chromations named after their colors, each applied by treating a galvanized surface with the appropriate aqueous chromating solution become. There are also yellow and green chromates for aluminum known, which are prepared in an analogous manner. It is about layers of different thicknesses with different corrosion protection effects, which essentially consist of amorphous zinc / chromium oxide (or aluminum / chromium oxide) with unstoichiometric Composition, a certain water content and built-in foreign ions consist. Known and according to DIN 50960 part 1 in process groups are divided into:

1. Colorless and blue chromate

The blue chromate layer is up to 80 nm thick, pale blue in its own color and depending on the layer thickness a golden, reddish, bluish, greenish or yellow iris color produced by light refraction. Very thin Chromate layers with almost no inherent color are called colorless chromate coatings designated. The chromating solution can in both cases both chromium (III) and chromium (VI) compounds in aqueous solution and Mixtures of both, and also consist of conductive salts and acids. There are fluoride-containing and fluoride-free variants. The corrosion protection of undamaged blue chromating is 10-40 h in the salt spray test DIN 50021 SS until the first appearance of corrosion products.

2. Yellow chromating

Yellow chromate layers are about 0.25-1 µm thick, golden yellow in color and often iridescent red-green. The chromating solution consists essentially of chromium (VI) compounds, halides, chloride, conductive salts such as sulfate and / or nitrate and acids in aqueous solution. The yellow color results from the significant proportion (80-220 mg / m ² ) of hexavalent chromium, which is incorporated in addition to the trivalent chromium produced by the reduction in the layer formation. The corrosion protection of undamaged yellow chromating amounts to approximately 100-200 hours in the salt spray test according to DIN 50021 SS until the first appearance of corrosion products.

3. Olive chromating

The typical olive chromating layer is up to 1.5 µm thick and from olive green to olive brown in color. The chromating solution consists essentially of chromium (VI) compounds, conductive salts and carboxylic acids or mineral acids, in particular phosphates or phosphoric acid in aqueous solution. Suitable acids for olive chromating are, for example, sulfuric acid, phosphoric acid, formic acid or acetic acid. Significant amounts of chromium (VI) (300-400 mg / m ² ) are stored in the layer. The corrosion protection of undamaged olive chromate coatings is approximately 200-400 hours in the salt spray test according to DIN 50021 SS due to the high layer thickness until the first appearance of corrosion products.

4. Black chromating

The black chromating of zinc surfaces is based on a yellow or olive chromate, into the colloidal silver compounds can be stored as pigments. The chromate solutions have roughly the same composition as with yellow or olive chromating and additionally contain Silver ions. On zinc alloy layers such as zinc iron, zinc nickel or zinc cobalt are stored with a suitable composition of the reaction solution Iron, nickel or cobalt oxide as black pigment in the chromate layer, so that in these cases Silver or silver compounds are not required. In the chromate layers, according to the underlying yellow or olive chromating significant amounts of chromium (VI) incorporated. The corrosion protection from undamaged black chromating on zinc amounts to 50-150 h in the salt spray test DIN 50021 SS until the first appearance of corrosion products. Black chromations on zinc alloys allow a significantly higher corrosion protection.

5. Green chromating

Green chromating for aluminum is matt green and not irritating. The chromating solution essentially consists from dissolved in water Chromium (VI) compounds, conductive salts and mineral acids and in particular from Phosphates and silicofluorides.

In the prior art, thick Chromate layers with high corrosion protection on zinc surfaces mainly through treatment with dissolved, extremely toxic chromium (VI) compounds. Accordingly the chromate layers produced in this way contain considerable amounts of these highly toxic and carcinogenic chromium (VI) compounds that moreover not completely are immobilized in the layer.

Because of the toxicity and carcinogenic Effect of chromium (VI) has long been tried to prevent corrosion based on the significantly less toxic chromium (III). In particular, processes based on blue chromating were used developed by chromium (III), but often with functional disadvantages are afflicted. These disadvantages are thin passivation layers, in remaining residues of chromium (VI) and one due to the low Layer thickness weak corrosion protection.

From U.S. Patent 4,263,059 and DE 30 38 699 A1 passivation baths for blue chromating are known which consist of an acidic solution with trivalent chromium, a mineral or carboxylic acid and fluoride ions. The trivalent chromium is formed from hexavalent chromium by adding a reducing agent. Since the conversion to chromium (III) is not complete, it is possible for chromium (VI) to be incorporated into the passivation layer, which can lead to dermatoses, in particular if such coatings are used in the food industry.

Furthermore, attempts have long been made through an alternative approach to blue passivation under exclusive Manufacture using chromium (III). The acids used for this chromating often contain additional Oxidizing agents (US Pat. No. 4,171,231) and other additives such as Silicates and / or metal ions (U.S. Patents 4,384,902; 4,359 347; 4,367,099). Due to the addition of oxidizing agents but again not ensuring that the layers created are actually free of chromium (VI). Furthermore, the layers produced in this way result decorative blue or yellow chromated surfaces, but these only offer weak corrosion protection (maximum 6 h on 10% white rust) and are not afterwards colorable.

The DE 38 12 076 A1 describes a process for blue chromating using an acidic passivation solution which contains chromium (III) as the sole source of chromium ions as well as nitrate ions, fluoride and hydrochloric or nitric acid for adjusting the pH. The corrosion protection achieved with this bath is relatively weak and is around 44 to 50 h according to DIN 50021 SS.

The DE 196 15 664 A1 , to which full reference is made, summarizes the prior art prior to 1994. This publication describes a process for producing chromium (VI) -free passivation layers with a larger layer thickness and higher corrosion protection. Organic chelate ligands, in particular dicarboxylic acids, tricarboxylic acids and hydroxycarboxylic acids such as, for example, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, phthalic acid, terephthalic acid, ascorbic acid, succinic acid, succinic acid, acid, are added to the reaction solution. These chelate ligands form kinetically unstable complexes with chromium (III), from which this is released quickly and is incorporated into the growing ZnCrO layer at high reaction rates. Metal ions such as divalent cobalt ions in the form of soluble salts are added as an additional catalyst, which are intended to increase the reaction rate and the thickness growth of the chromate layer. The passivation layers produced in this way are free of chromium (VI) and allow corrosion protection of up to over 100 h, which corresponds approximately to that of conventional yellow chromating. The chromate layers produced in this way have a greenish, red-green iridescent color. An alternative, in the DE 41 35 524 A1 described passivation process based on a chromium (III) oxalate complex based, again provides a blue passivation film.

The above examples show that chromium (III) passivation still allow only limited application possibilities. Next the mostly weak corrosion protection with blue chromating and the risk of chromium (VI) residues especially the limited options The coloring that can be achieved with chromium (III) passivation is disadvantageous.

The through chromium (III) passivation limit generated colors mainly on blue and greenish chromate layers, while yellow chromates on a chromium (III) basis do not allow uniform and strong yellow coloring, but rather bright, clearly iridescent or going bluish or greenish Coatings.

Therefore, attempts have been repeated attempted to create yellow passivation layers that only have one have a low chromium (VI) content or are free of chromium (VI). Because the intense yellow color with conventional Yellow chromations caused by chromium (VI) itself have been the reaction solutions Pigments added by their incorporation in the passivation layer to be stronger yellow shades to lead should.

U.S. Patent 4,384,902 describes the addition of cerium ions as a color pigment. The one contained in the bathroom solution Cerium (III) becomes cerium (VI) when separated by hydrogen peroxide oxidized, which has a yellowish tinge causes. Although the reaction solution is chromium (III) for passivation used, the resulting passivation layer is not free of chrome (VI). This explains from the fact that Cerium (VI) produced a stronger one Is oxidizing agent as chromium (VI) so that cerium (VI) the formation of chromium (VI) made of chrome (III). About that Furthermore, Cer is due to its rarity and high price in practice a little beneficial dye.

Further experiments with subsequently applied Color pigments on passivation layers containing chromium (VI) are failed because the Chromium (VI) dye destroyed the corrosion protection has deteriorated due to re-diving was (see blue pigments).

Through the variable training of Passivation layer also occurs in the subsequent dye too strong fluctuations in color depth and a related severe visual impairment of the treated parts.

The invention is therefore the object color pigments, mixtures of substances and processes for chromium (III) passivation provide the generation of largely chromium (VI) -free colored Passivation layers, especially color-intensive and color-intensive ones yellow passivation layers.

This task is accomplished by the main claim mentioned mixture of substances and the preferred embodiments of the subclaims and solved by the claimed method. The invention is based on the use of an aqueous acidic Reaction solution, which contains trivalent chromium ions and a quinoline dye. The Term includes quinoline dye any pigment that has a quinoline skeleton or a quinoline residue contains.

With the quinoline dyes used for this for example, the well-known dyes quinoline yellow, Trade quinoline red and quinoline blue.

In a preferred embodiment quinoline yellow is used. This from the area of food colors Known pigment is usually a mixture of chemically related Pigments from quinoline, or quinaldine and phthalic anhydride assemble and sulfonate at different positions of the molecule could be.

In a particularly preferred embodiment Basacid Yellow 094 ^® is used one made by BASF form of the quinoline. Basacid ^® Yellow 094 contains the two pigments shown below, the first of which is the main pigment or the group of main pigments:

These pigments are about anionic molecules which each have 2 or 3 sulfonic acid residues exhibit. These pigments are synthesized by sulfonation. The sulfonic acid residues are either on the benzo group of the quinoline or on the benzene ring of the second Aromatics, a derivative of phthalic anhydride.

Advantageous concentrations of Basacid ^® Yellow 094 or another dye or dye mixture according to the present invention can vary widely depending on the desired color intensity and can be, for example, between 0.1 and 20 g / l in the reaction solution. Preferred average dye concentrations in the reaction solution can be, for example, between 0.7 and 1.0 g / l.

The other constituents, additives and reaction conditions can be analogous to one or more of the in DE 196 15 664 A1 described components can be selected.

The pH of the reaction solution used for the implementation can for example approximately between 1.5 and 3.0, preferably lies he between 1.8 and 2.2. The desired pH can be adjusted by adding nitric acid or another mineral or carboxylic acid and then with Sodium hydroxide solution can be set exactly.

The concentration of dissolved chromium (III) ions can range from 200 mg / l to the solubility limit pass. Preferred concentration ranges are in the application solution between 2 and 10 g / l. Chromium chloride or another can be used as the source of the chromium (III) ions water-soluble Chromium (III) salt can be used.

Chelate ligands can be added to the reaction solution, which advantageously influence the reaction rate and the layer thickness achieved. These chelating ligands are preferably organic substances, in particular dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids, acetylacetone, urea and urea derivatives. The use of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, phthalic acid, terephthalic acid, ascorbic acid, malic acid, tartaric acid or citric acid is particularly preferred. The use of oxalic acid has the further advantage that it can make Fe ²⁺ ions which are formed in the treatment of galvanized iron parts insoluble.

As additional catalysts 2- up to 6-valent metal ions such as Al, Co, Ni, Fe, Ga, In, lanthanides, Zr, Sc, Ti, V, Cr, Mn, Cu, Zn, Y, Nb, Mo, Hf, Ta and W contained in the reaction solution be that of the reaction solution as soluble Salts are added. In a preferred embodiment are cobalt (II) ions in a concentration of about 0.1 to 5 g / I included. Here, hydrous or anhydrous cobalt nitrates, Cobalt sulfates or cobalt chloride Examples of suitable cobalt (II) sources represents.

As further components and guide ions can the reaction solution Halides, especially chloride and fluoride, sulfate ions, nitrate ions, Phosphoric acid, organophosphate or phosphate ions, silications, silicas, amino acids, amines and contain surfactants.

The reaction is preferably carried out at Bath temperatures from approx. 20 to 100 ° C. Particularly preferred bath temperatures are between 40 and 60 ° C. The diving time can be between 15 and 200 seconds; in a preferred embodiment it is between 30 and 90 sec.

The reaction solution can be any suitable one Technology such as diving, spray diving, spraying or brushing on the treating object are applied.

The following is the yellow chromating according to the invention based on a specific embodiment being represented.

Application solution (reaction solution):
3.1 g / l chromium (III) as chromium nitrate
4.0 g / l oxalic acid
2.4 g / l cobalt (II) as cobalt nitrate
4.8 g / l citric acid
0.2 g / l methanol (for the safe reduction of chromium (VI) residues)

Depending on the desired color intensity, 0.7-1.0 g / l of Basacid ^® Yellow 094 dye are added. The pH of this finished application solution is adjusted to a pH of 2.0 with sodium hydroxide solution. The reaction takes place at a temperature of 45 ° C and with a dipping time of 30-50 sec. The treated parts are rinsed and dried. The resulting chromate layer containing dye is characterized by a strong, uniform, non-iridescent color. Their corrosion resistance according to DIN 50021 SS is at least 50 h in the salt spray cabinet and between 60 and 160 h in the salt spray test.

Claims (32)

Reaction solution for the passivation of zinc and zinc alloys, consisting of an aqueous acidic reaction solution with trivalent chromium ions, characterized in that the reaction solution contains at least one quinoline dye. reaction solution according to claim 1, characterized by quinoline yellow, quinoline red or quinoline blue. reaction solution according to claim 1 or 2, characterized by one or more pigments of the quinoline yellow dye. reaction solution according to one of the preceding claims, characterized by Basacid® Yellow 094 from BASF as a pigment or pigment mixture. reaction solution according to one of the preceding claims, characterized by one of quinoline or a quinoline derivative and phthalic anhydride, or a derivative of phthalic anhydride composite pigment. reaction solution according to one of the preceding claims, characterized by a pigment with one or more sulfonic acid residues. reaction solution according to one of the preceding claims, characterized by an anionic pigment. reaction solution according to one of the preceding claims, characterized by a food coloring. reaction solution according to one of the preceding claims, characterized by a concentration range of the dye or dye mixture from 0.1 g / l to 20 g / l. reaction solution according to one of the preceding claims, characterized by a concentration range of the dye or dye mixture from 0.7 g / l to 1.0 g / l. reaction solution according to one of the preceding claims, characterized by a pH of 1.5 to 3.0. reaction solution according to one of the preceding claims, characterized by a pH of 1.8 to 2.2. reaction solution according to one of the preceding claims, characterized by a concentration of the dissolved chromium (III) ions of 200 mg / l up to the solubility limit. reaction solution according to one of the preceding claims, characterized by a concentration of the dissolved chromium (III) ions of 2 up to 10 g / l. reaction solution according to one of the preceding claims, characterized by chelating ligands from a group comprising dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids, acetylacetone, Urea and urea derivatives. reaction solution according to one of the preceding claims, characterized by chelating ligands from a group comprising oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, phthalic acid, terephthalic acid, ascorbic acid, malic acid, tartaric acid or Citric acid. reaction solution according to one of the preceding claims, characterized by 2-6-valent metal ions from a group comprising Al, Co, Ni, Fe, Ga, In, Lanthanide, Zr, Sc, Ti, V, Cr, Mn, Cu, Zn, Y, Nb, Mo, Hf, Ta and W. reaction solution according to one of the preceding claims, characterized by cobalt (II) ions in a concentration of about 0.1 to 5 g / l. reaction solution according to one of the preceding claims, characterized by halides, especially chloride and fluoride, Sulfate ions, nitrate ions, phosphoric acid, phosphoric acid esters or phosphate ions, silications, silicas, amino acids, amines and / or surfactants. Process for the passivation of zinc and zinc alloys based on an aqueous acidic reaction solution containing trivalent chromium ions, characterized in that the reaction solution at least one quinoline dye is added. A method according to claim 20, characterized by a reaction temperature of about 40 to 60 ° C. A method according to claim 20 or 21, characterized due to a diving time of about 30 to 90 seconds. Passivation layer for zinc and zinc alloys, largely free of chromium (VI), characterized by the coloring the layer by adding one of the passivation solution added Dye in the passivation layer with a corrosion protection of at least 50 h in a salt spray cabinet according to DIN 50021 SS. Passivation layer according to claim 23, characterized through the storage of an organic dye. Passivation layer according to claim 23 or 24, characterized by storing a quinoline dye. Passivation layer according to one of the preceding claims, characterized through the storage of quinoline yellow. Passivation layer according to one of the preceding claims, characterized through the storage of Basacid® Yellow 094 or one of the pigments contained therein. Passivation layer according to one of the preceding claims, characterized due to a yellow, non-iridescent color of the passivation layer. Passivation layer according to one of the preceding claims, characterized by corrosion protection from about 60 to 160 hours in the salt spray test DIN 50021 SS. Use of quinoline dyes for production colored passivation layers on zinc and zinc alloys. Use according to claim 30, characterized by Quinoline yellow. Use according to claim 30 or 31, characterized with Basacid® Yellow 094 from BASF.