EP0328908B1 - Process for applying conversion coatings - Google Patents
Process for applying conversion coatings Download PDFInfo
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- EP0328908B1 EP0328908B1 EP89101302A EP89101302A EP0328908B1 EP 0328908 B1 EP0328908 B1 EP 0328908B1 EP 89101302 A EP89101302 A EP 89101302A EP 89101302 A EP89101302 A EP 89101302A EP 0328908 B1 EP0328908 B1 EP 0328908B1
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- metal surfaces
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/60—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using alkaline aqueous solutions with pH greater than 8
- C23C22/66—Treatment of aluminium or alloys based thereon
- C23C22/67—Treatment of aluminium or alloys based thereon with solutions containing hexavalent chromium
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/60—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using alkaline aqueous solutions with pH greater than 8
Definitions
- the invention relates to a method for applying conversion coatings on metal surfaces made of aluminum, zinc and their alloys with the aid of solutions containing alkaline ChromVI and ChromIII.
- the concentration of the hexavalent chromium is approximately 13 g / l (expressed as CrO3), but the concentration of the dissolved trivalent chromium is extremely low, approximately in the order of 1 ppm, even if the solution is saturated with chromium III oxide. The reason is the very low solubility of the trivalent chromium at high pH values of the solution.
- the relatively thick conversion coating obtained by this process consists essentially of aluminum and chromium III oxide.
- the aforementioned method has numerous disadvantages.
- the appearance of the conversion coating formed is very different, for example stained or marbled green and / or brown.
- the treatment requires a diving time of about 5 minutes at a temperature of 90 to 100 ° C.
- the high content of hexavalent chromium in the solution requires extensive treatment of the waste water.
- GB-PS 899 599 provides for essentially colorless chromate coatings on surfaces of zinc or conventional zinc alloys by treatment with a strongly acidic (pH 0.2 to 2.8) solution containing hexavalent chromium and trivalent chromium produce.
- concentration of the hexavalent chromium is around 10 g / l (calculated as chromium VI oxide) and is therefore also complex with regard to the required wastewater treatment.
- the strongly acidic reaction of the chromating solution also makes the solution very aggressive, so that material suitable for plant construction is only available to a limited extent.
- this method cannot be used satisfactorily for the treatment of aluminum, since acidic solutions tend to be somewhat ineffective on aluminum if they do not contain fluoride.
- the use of solutions containing acid fluoride in turn leads to unsatisfactory results in the treatment of zinc.
- GB-PS 1 042 108 describes a method for the treatment of zinc and conventional zinc alloys, in which the zinc surfaces are treated with a chromium VI-free aqueous alkaline solution, the pH of which is above 11 and which is one of the Group 1 of the periodic system contains different metal, brought into contact.
- the majority of the examples show the use of metals such as iron, cobalt or magnesium, whereas trivalent chromium is not mentioned as a suitable metal.
- the use of hexavalent chromium is expressly excluded, since it allegedly affects the formation of the desired conversion coating.
- DE-A1-37 11 095 is a method for producing conversion coatings on Zn or Zn alloy surfaces by means of aqueous solutions, the Cr (III) ions and ions of at least two other multivalent metals, preferably Fe (III) ions, and Contains Co and / or Ni ions and complexing agents and whose pH is greater than 11, known.
- the object of the invention is to provide a method which allows the treatment of pure aluminum, pure zinc, but also of alloys of zinc or aluminum with other metals, but in particular the treatment of zinc / aluminum alloys using the same solutions.
- the object is achieved by designing the method of the type mentioned at the outset in accordance with the invention in such a way that the metal surfaces are brought into contact with a solution which, owing to the addition of a Complexing agent for ChromIII contains at least 20 ppm dissolved ChromIII.
- the complexing agent can be used to adjust the concentrations of the chromium III to such considerably higher values.
- the hexavalent chromium can be introduced into the treatment solutions in the form of suitable soluble chromates, preferably as alkali chromates. If the concentration of hexavalent chromium is too low, the required conversion coating does not take place, so that the protection achieved is inadequate. If the concentrations are too high, there is a tendency to passivate the metal surfaces instead of forming a conversion coating formed by reaction.
- the metal surfaces are brought into contact with a solution which contains 8 to 75 ppm of ChromVI. It is particularly advantageous to bring the metal surfaces into contact with a solution that contains 15 to 60 ppm ChromVI.
- the trivalent chromium can be added as any suitable soluble chromium compound, especially as a chromium salt.
- the conversion coating produced by the process according to the invention is usually rinsed with water, it is desirable to use a salt with an anion which does not cause any corrosion problems.
- a further advantageous embodiment of the invention therefore provides for the metal surfaces to be brought into contact with a solution in which the chromium III is introduced as nitrate, sulfate, phosphate and / or acetate.
- Halides, especially chlorides should preferably not be used.
- chromium III carbonate can also be used, but this requires the presence of an initially acidic solution, which is then made alkaline by adding alkali.
- Another way of achieving the required chromium III content in the solution is to produce it by reducing the excess hexavalent chromium which has previously been introduced.
- the reduction required for this usually takes place in an acidic medium, so that alkali must subsequently be added.
- the reduction can, for example, be brought about by introducing organic reducing agents into the solution in a manner known per se.
- the concentration of trivalent chromium is below 30 ppm, the conversion coating can be formed relatively slowly. Accordingly, an advantageous development of the invention provides for the metal surfaces to be brought into contact with a solution which contains at least 30 ppm, preferably even at least 50 ppm, of chromium III. It is particularly advantageous to adjust the concentration of trivalent chromium to a maximum of 700 ppm, preferably to 100 to 500 ppm. At concentrations above 700 ppm, no further advantages are usually achieved.
- the pH of the solution should be above 12, otherwise the process takes place with too slow a coating formation.
- the setting of a pH value of at least 12.5 is particularly advantageous.
- the pH value is usually determined by a suitable one which does not impair the formation of the coating Alkali made.
- the use of sodium silicate should be avoided, since a sodium silicate content tends to passivate individual surfaces, particularly those made of aluminum.
- Sodium carbonate can be used, but the required pH cannot be achieved with it, so that additional pH adjustment with alkali hydroxide is required. It is therefore most expedient to use alkali hydroxide, in particular sodium and / or potassium hydroxide, for the entire pH adjustment.
- the amount of the hydroxides is generally at least 10 g / l, but is below 80 g / l. If the concentration is too high, there is a risk that the solution will vigorously etch the zinc and aluminum surface and fail to provide the desired coating.
- any compound capable of keeping the required amounts of trivalent chromate in solution can be used as the complexing agent.
- the metal surfaces are brought into contact with a solution which is used as a complexing agent for chromium III hydroxycarboxylic acid, in particular gluconic acid and / or hexahydroxy heptanoic acid, such as glucoheptanoic acid, or but contains as a complexing agent for ChromIII aminocarboxylic acid, in particular nitrilotriacetic acid and / or ethylenediaminetetraacetic acid.
- Citric acid is suitable as the hydroxy carboxylic acid, albeit less advantageously.
- the aforementioned acids can also be introduced into the solution in the form of their sodium salts.
- aminocarboxylic acid especially in combination with hydroxycarboxylic acid, has the advantage that the effectiveness of the method is increased by a more uniform pickling attack on the metal surface and the formation of a particularly uniform conversion coating.
- the metal surfaces are brought into contact with a solution which contains the hydroxycarboxylic acid in an amount of 0.2 to 10 g / l or the aminocarboxylic acid in an amount of 0.5 to 10 g / l .
- the aforementioned quantities refer to the neutral sodium salts.
- the solution required to carry out the method according to the invention can be prepared by dissolving the individual constituents in water while adjusting the concentrations required in each case.
- the alkali required for pH adjustment can be added separately or already contained in the batch concentrate.
- Suitable concentrates usually have a solids content of 15 to 40% by weight, in particular 25 to 35% by weight. They contain the effective solution components in the ratio in which they are also contained in the working solution. This makes it possible to prepare the working solution by simply diluting it with the appropriate amount of water.
- the method according to the invention can be applied in any known manner, the treatment of the metal surfaces in spraying or immersion is preferred.
- the treatment time can be very short, for example 5 to 15 s, but longer treatment times, for example up to 1 minute, are also possible. The latter applies in particular when the concentration of trivalent chromium and / or the treatment temperatures are comparatively low.
- the temperature of the solution to be brought into contact with the metal surface is normally below 70 ° C, generally in the range of 40 to 60 ° C.
- the workpieces to be treated are generally at a temperature of 30 to 50 ° C, usually at about 40 ° C before treatment.
- the conversion coating formed by the process according to the invention is generally rinsed with water, generally by spraying. Furthermore, it is advantageous to carry out a passivation rinse with a chromate solution, preferably as described in GB-PS 1 084 478, following the application of the conversion coating. This is followed by drying.
- the conversion coatings produced with the method according to the invention have good corrosion resistance. You can stay without further post-treatment, but in general it is common to apply a varnish afterwards, which can be both colorless and colored.
- the method according to the invention is advantageously applicable to the treatment of zinc, aluminum and their alloys with other metals or with one another.
- the invention is particularly advantageous if the intention is to treat different metal surfaces simultaneously or subsequently.
- hot-dip galvanized or hot-dip galvanized steel strip can be treated without having to change the nature of the solution.
- the aforementioned solution was sprayed on at 50 ° C. for 15 seconds onto steel strip which was hot-dip galvanized or hot-dip coated with a zinc / aluminum alloy.
- the alloy consisted of 5% by weight aluminum and 95% by weight zinc. Following the conversion treatment, it was rinsed with water in a syringe and dried. An epoxy primer and a top coat made of a silicone-modified polyester were then applied.
- the steel strip treated in this way was treated in the salt spray test in accordance with ASTM-B 117 for a period of 1500 h. The subsequent evaluation showed that, based on the cross-cut, the paint had infiltrated ⁇ 1 mm.
- a concentrate was made that contains, manufactured.
- a working solution can be prepared from the aforementioned concentrate by dilution with water in a ratio of 1:10.
Description
Die Erfindung betrifft ein Verfahren zum Aufbringen von Konversionsüberzügen auf Metalloberflächen aus Aluminium, Zink und deren Legierungen mit Hilfe alkalischer ChromVI und ChromIII enthaltender Lösungen.The invention relates to a method for applying conversion coatings on metal surfaces made of aluminum, zinc and their alloys with the aid of solutions containing alkaline ChromVI and ChromIII.
Es ist bekannt, auf Aluminium und herkömmlichen Aluminium-Legierungen aus alkalischen Chromatlösungen, die dreiwertiges Chrom enthalten, Konversionsüberzüge aufzubringen. So sieht das Verfahren gemäß GB-PS 441 088 vor, Metalloberflächen mit einer wäßrigen Lösung in Kontakt zu bringen, die Natriumcarbonat, Natriumchromat und eine dritte Komponente, die als Natriummonohydrogenphosphat oder ChromIII-Carbonat bezeichnet ist, enthält. In der Praxis wird der Prozeß in der Weise ausgeführt, daß man eine Tauchbehandlung in einer heißen wäßrigen Lösung von Natriumcarbonat, Natriumchromat und ChromIII-Oxid vornimmt. Dabei liegt die Konzentration des sechswertigen Chroms etwa bei 13 g/l (ausgedrückt als CrO₃), jedoch ist die Konzentration des gelösten dreiwertigen Chromas extrem niedrig, etwa in der Größenordnung von 1 ppm, selbst wenn die Lösung bezüglich ChromIII-Oxid gesättigt ist. Der Grund liegt in der sehr geringen Löslichkeit des dreiwertigen Chroms bei hohen pH-Werten der Lösung. Der nach diesem Verfahren erhaltene relativ dicke Konversionsüberzug besteht im wesentlichen aus Aluminium- und ChromIII-Oxid.It is known to apply conversion coatings to aluminum and conventional aluminum alloys from alkaline chromate solutions containing trivalent chromium. Thus, the method according to GB-PS 441 088 provides to bring metal surfaces into contact with an aqueous solution which contains sodium carbonate, sodium chromate and a third component, which is referred to as sodium monohydrogen phosphate or chromium III carbonate. In practice, the process is carried out by dipping in a hot aqueous solution of sodium carbonate, sodium chromate and chromium III oxide. The concentration of the hexavalent chromium is approximately 13 g / l (expressed as CrO₃), but the concentration of the dissolved trivalent chromium is extremely low, approximately in the order of 1 ppm, even if the solution is saturated with chromium III oxide. The reason is the very low solubility of the trivalent chromium at high pH values of the solution. The relatively thick conversion coating obtained by this process consists essentially of aluminum and chromium III oxide.
Das vorgenannte Verfahren weist zahlreiche Nachteile auf. Beispielsweise ist das Aussehen des gebildeten Konversionsüberzuges sehr unterschiedlich, beispielsweise fleckig oder marmoriert grün und/oder braun. Die Behandlung erfordert eine Tauchdauer von etwa 5 Minuten bei einer Temperatur von 90 bis 100°C. Der hohe Gehalt an sechswertigem Chrom in der Lösung erfordert eine aufwendige Behandlung der Abwasser. Insbesondere diese vorgenannten Nachteile begrenzen die Anwendbarkeit des Verfahrens auf Aluminium und lassen es für die Behandlung von Zink-Oberflächen als ungeeignet erscheinen.The aforementioned method has numerous disadvantages. For example, the appearance of the conversion coating formed is very different, for example stained or marbled green and / or brown. The treatment requires a diving time of about 5 minutes at a temperature of 90 to 100 ° C. The high content of hexavalent chromium in the solution requires extensive treatment of the waste water. These aforementioned disadvantages in particular limit the applicability of the process to aluminum and make it appear unsuitable for the treatment of zinc surfaces.
In der GB-PS 899 599 ist vorgesehen, im wesentlichen farblose Chromatüberzüge auf Oberflächen von Zink oder herkömmlichen Zink-Legierungen durch Behandlung mit einer stark sauren (pH 0,2 bis 2,8) Lösung, die sechswertiges Chrom und dreiwertiges Chrom enthält, zu erzeugen. Die Konzentration des sechswertigen Chroms liegt bei etwa 10 g/l (gerechnet als ChromVI-Oxid) und ist mithin ebenfalls aufwendig hinsichtlich der erforderlichen Abwasserbehandlung. Die stark saure Reaktion der Chromatierungslösung macht zudem die Lösung sehr aggressiv, so daß für den Anlagenbau geeignetes Material nur in eingeschränkter Weise zur Verfügung steht. Darüber hinaus kann dieses Verfahren nicht in zufriedenstellender Weise für die Behandlung von Aluminium verwendet werden, da saure Lösungen zu einer gewissen Ineffektivität auf Aluminium neigen, wenn sie nicht Fluorid enthalten. Die Verwendung von saures Fluorid enthaltenden Lösungen führt wiederum bei der Behandlung von Zink zu unbefriedigenden Ergebnissen.GB-PS 899 599 provides for essentially colorless chromate coatings on surfaces of zinc or conventional zinc alloys by treatment with a strongly acidic (pH 0.2 to 2.8) solution containing hexavalent chromium and trivalent chromium produce. The concentration of the hexavalent chromium is around 10 g / l (calculated as chromium VI oxide) and is therefore also complex with regard to the required wastewater treatment. The strongly acidic reaction of the chromating solution also makes the solution very aggressive, so that material suitable for plant construction is only available to a limited extent. Furthermore, this method cannot be used satisfactorily for the treatment of aluminum, since acidic solutions tend to be somewhat ineffective on aluminum if they do not contain fluoride. The use of solutions containing acid fluoride in turn leads to unsatisfactory results in the treatment of zinc.
Schließlich ist in der GB-PS 1 042 108 ein Verfahren zur Behandlung von Zink und herkömmlichen Zink-Legierungen beschrieben, bei dem die Zink-Oberflächen mit einer ChromVI-freien wäßrigen alkalischen Lösung, deren pH-Wert über 11 liegt und die ein von der Gruppe 1 des periodischen Systems verschiedenes Metall enthält, in Kontakt gebracht. Die Mehrzahl der Beispiele zeigt eine Verwendung von Metallen wie Eisen, Kobalt oder Magnesium, dreiwertiges Chrom hingegen ist nicht als ein geeignetes Metall genannt. Die Verwendung von sechswertigem Chrom ist ausdrücklich ausgeschlossen, da es angeblich die Ausbildung des erwünschten Konversionsüberzuges beeinträchtigt.Finally, GB-PS 1 042 108 describes a method for the treatment of zinc and conventional zinc alloys, in which the zinc surfaces are treated with a chromium VI-free aqueous alkaline solution, the pH of which is above 11 and which is one of the Group 1 of the periodic system contains different metal, brought into contact. The majority of the examples show the use of metals such as iron, cobalt or magnesium, whereas trivalent chromium is not mentioned as a suitable metal. The use of hexavalent chromium is expressly excluded, since it allegedly affects the formation of the desired conversion coating.
Nach der DE-A1-37 11 095 ist ein Verfahren zum Erzeugen von Konversionssüberzügen auf Zn- oder Zn- Legierungsoberflächen mittels wässriger Lösungen, die Cr(III)-lonen und lonen mindestens zweier weiterer mehrwerfiger Metalle, vorzugsweise Fe(III)-lonen sowie Co- und/oder Ni-lonen sowie Komplexbildner enthält und deren pH-Wert größer als 11 ist, bekannt.According to DE-A1-37 11 095 is a method for producing conversion coatings on Zn or Zn alloy surfaces by means of aqueous solutions, the Cr (III) ions and ions of at least two other multivalent metals, preferably Fe (III) ions, and Contains Co and / or Ni ions and complexing agents and whose pH is greater than 11, known.
Herkömmliche Zink-Legierungen sind im wesentlichen frei von Aluminium und herkömmliche Aluminium-Legierungen im wesentlichen frei von Zink. In jüngerer Zeit sind jedoch Zink/Aluminium-Legierungen entwickelt worden, die beträchtliche Gehalte von sowohl Zink als auch Aluminium aufweisen. Typische Beispiele besitzen ein Gehalt von 97 Gew.-% Zink und 3 Gew.-% Aluminium bis 30 Gew.-% Zink und 70 Gew.-% Aluminium. Besonders wichtige Legierungen der vorgenannten Art sind die mit 5 Gew.-% Aluminium und 95 Gew.-% Zink sowie 55 Gew.-% Aluminium und 45 Gew.-% Zink. Diese Legierungen sind mit Zink und konventionellen Zink-Legierungen bei der Herstellung von schmelztauchverzinktem Stahl oder anderweitig beschichtetem Stahl austauschbar. Es wäre daher wünschenswert, über ein Behandlungsverfahren zu verfügen, das im Verhältnis zu beiden Arten von Metalloberflächen wirksam ist, d.h. daß für die Behandlung von mit Zink aber auch mit Zink/Aluminium-Legierungen plattiertes Stahlband anwendbar ist.Conventional zinc alloys are essentially free of aluminum and conventional aluminum alloys are essentially free of zinc. More recently, however, zinc / aluminum alloys have been developed that have substantial levels of both zinc and aluminum. Typical examples have a content of 97% by weight zinc and 3% by weight aluminum to 30% by weight zinc and 70% by weight aluminum. Particularly important alloys of the aforementioned type are those with 5% by weight aluminum and 95% by weight zinc and 55% by weight aluminum and 45% by weight zinc. These alloys are interchangeable with zinc and conventional zinc alloys in the manufacture of hot dip galvanized steel or other coated steel. It would therefore be desirable to have a treatment process that is effective in relation to both types of metal surfaces, i.e. that for the treatment of zinc plated but also with zinc / aluminum alloys steel strip is applicable.
Aufgabe der Erfindung ist es, ein Verfahren bereitzustellen, das sowohl die Behandlung von reinem Aluminium, reinem Zink, aber auch von Legierungen von Zink oder Aluminium mit anderen Metallen, insbesondere aber die Behandlung von Zink/Aluminium-Legierungen unter Verwendung gleicher Lösungen gestattet.The object of the invention is to provide a method which allows the treatment of pure aluminum, pure zinc, but also of alloys of zinc or aluminum with other metals, but in particular the treatment of zinc / aluminum alloys using the same solutions.
Die Aufgabe wird gelöst, indem das Verfahren der eingangs genannten Art entsprechend der Erfindung derart ausgestaltet wird, daß man die Metalloberflächen mit einer Lösung in Kontakt bringt, die infolge des Zusatzes eines Komplexbildners für ChromIII mindestens 20 ppm gelöstes ChromIII enthält.The object is achieved by designing the method of the type mentioned at the outset in accordance with the invention in such a way that the metal surfaces are brought into contact with a solution which, owing to the addition of a Complexing agent for ChromIII contains at least 20 ppm dissolved ChromIII.
Im Unterschied zu Behandlungslösungen, die üblicherweise einen pH-Wert von etwa 12 aufweisen und dabei lediglich ca. 1 ppm ChromIII gelöst enthalten, gelingt es durch Zugabe des Komplexbildners, die Konzentrationen des ChromIII auf derartig beträchtlich höhere Werte einzustellen.In contrast to treatment solutions, which usually have a pH of about 12 and contain only about 1 ppm of chromium III dissolved, the complexing agent can be used to adjust the concentrations of the chromium III to such considerably higher values.
Das sechswertige Chrom kann in die Behandlungslösungen in Form geeigneter löslicher Chromate, vorzugsweise als Alkalichromate, eingebracht werden. Sofern die Konzentration an sechswertigem Chrom zu gering ist, findet die erforderliche Ausbildung des Konversionsüberzuges nicht statt, so daß der damit erzielte Schutz unzulänglich ist. Sofern die Konzentrationen zu hoch sind, besteht die Tendenz zur Passivierung der Metalloberflächen anstelle der Ausbildung eines durch Reaktion entstehenden Konversionsüberzuges.The hexavalent chromium can be introduced into the treatment solutions in the form of suitable soluble chromates, preferably as alkali chromates. If the concentration of hexavalent chromium is too low, the required conversion coating does not take place, so that the protection achieved is inadequate. If the concentrations are too high, there is a tendency to passivate the metal surfaces instead of forming a conversion coating formed by reaction.
Gemäß einer bevorzugten Ausgestaltung der Erfindung bringt man die Metalloberflächen mit einer Lösung in Kontakt, die 8 bis 75 ppm ChromVI enthält. Besonders vorteilhaft ist es, die Metalloberflächen mit einer Lösung in Kontakt zu bringen, die 15 bis 60 ppm ChromVI enthalten.According to a preferred embodiment of the invention, the metal surfaces are brought into contact with a solution which contains 8 to 75 ppm of ChromVI. It is particularly advantageous to bring the metal surfaces into contact with a solution that contains 15 to 60 ppm ChromVI.
Das dreiwertige Chrom kann als jede geeignete lösliche Chrom-Verbindung, insbesondere als Chromsalz, zugegeben werden. Obwohl der nach dem erfindungsgemäßen Verfahren erzeugte Konversionsüberzug üblicherweise mit Wasser gespült wird, ist es wünschenswert, ein Salz mit einem Anion einzusetzen, das keine Korrosionsprobleme verursacht. Daher sieht eine weitere vorteilhafte Ausgestaltung der Erfindung vor, die Metalloberflächen mit einer Lösung in Kontakt zu bringen, in die das ChromIII als Nitrat, Sulfat, Phosphat und/oder Acetat eingebracht ist. Halogenide, insbesondere Chloride, sollten vorzugsweise nicht verwendet werden. Im Prinzip kann auch ChromtIII-Carbonat verwendet werden, jedoch setzt dies das Vorhandensein einer zunächst sauren Lösung voraus, die anschließend durch Zugabe von Alkali alkalisch eingestellt wird.The trivalent chromium can be added as any suitable soluble chromium compound, especially as a chromium salt. Although the conversion coating produced by the process according to the invention is usually rinsed with water, it is desirable to use a salt with an anion which does not cause any corrosion problems. A further advantageous embodiment of the invention therefore provides for the metal surfaces to be brought into contact with a solution in which the chromium III is introduced as nitrate, sulfate, phosphate and / or acetate. Halides, especially chlorides, should preferably not be used. In principle, chromium III carbonate can also be used, but this requires the presence of an initially acidic solution, which is then made alkaline by adding alkali.
Eine weitere Möglichkeit, den erforderlichen Gehalt an ChromIII in der Lösung herbeizuführen, besteht darin, dieses durch Reduktion von zuvor eingebrachten überschüssigem sechswertigem Chrom zu erzeugen. Die hierfür erforderliche Reduktion geschieht üblicherweise im sauren Milieu, so daß anschließend Alkali-Zusatz erforderlich ist. Die Reduktion kann beispielsweise durch Einbringung organischer Reduktionsmittel in die Lösung in an sich bekannter Weise herbeigeführt werden.Another way of achieving the required chromium III content in the solution is to produce it by reducing the excess hexavalent chromium which has previously been introduced. The reduction required for this usually takes place in an acidic medium, so that alkali must subsequently be added. The reduction can, for example, be brought about by introducing organic reducing agents into the solution in a manner known per se.
Sofern die Konzentration an dreiwertigem Chrom unterhalb 30 ppm liegt, kann die Ausbildung des Konversionsüberzuges relativ langsam erfolgen. Demzufolge sieht eine vorteilhafte Weiterbildung der Erfindung vor, die Metalloberflächen mit einer Lösung in Kontakt zu bringen, die mindestens 30 ppm, vorzugsweise sogar mindestens 50 ppm, ChromIII enthält. Besonders vorteilhaft ist es, die Konzentration an dreiwertigem Chrom auf maximal 700 ppm, vorzugsweise auf 100 bis 500 ppm, einzustellen. Bei Konzentrationen oberhalb von 700 ppm werden in der Regel keine weiteren Vorteile erzielt.If the concentration of trivalent chromium is below 30 ppm, the conversion coating can be formed relatively slowly. Accordingly, an advantageous development of the invention provides for the metal surfaces to be brought into contact with a solution which contains at least 30 ppm, preferably even at least 50 ppm, of chromium III. It is particularly advantageous to adjust the concentration of trivalent chromium to a maximum of 700 ppm, preferably to 100 to 500 ppm. At concentrations above 700 ppm, no further advantages are usually achieved.
Der pH-Wert der Lösung sollte oberhalb 12 liegen, da ansonsten das Verfahren mit einer zu langsamen Überzugsausbildung abläuft. Besonders vorteilhaft ist die Einstellung eines pH-Wertes von wenigstens 12,5. Der pH-Wert wird üblicherweise durch ein geeignetes, keine Beeinträchtigung der Überzugsausbildung herbeiführendes Alkali vorgenommen. So sollte beispielsweise auf die Verwendung von Natriumsilikat verzichtet werden, da ein Natriumsilikat-Gehalt zur Passivierung einzelner Oberflächen, insbesondere solcher aus Aluminium, tendiert. Natriumcarbonat kann verwendet werden, jedoch ist der erforderliche pH-Wert hiermit nicht erzielbar, so daß eine ergänzende pH-Einstellung mit Alkalihydroxid erforderlich ist. Am zweckmäßigsten ist es daher, für die gesamte pH-Einstellung Alkalihydroxid, insbesondere Natrium- und/oder Kaliumhydroxid, zu verwenden. Die Menge der Hydroxide beträgt im allgemeinen wenigstens 10 g/l, liegt jedoch unterhalb 80 g/l. Wenn die Konzentration zu hoch ist, besteht die Gefahr, daß die Lösung die Zink- und Aluminium-Oberfläche heftig anätzt und die erwünschte Überzugsausbildung ausbleibt.The pH of the solution should be above 12, otherwise the process takes place with too slow a coating formation. The setting of a pH value of at least 12.5 is particularly advantageous. The pH value is usually determined by a suitable one which does not impair the formation of the coating Alkali made. For example, the use of sodium silicate should be avoided, since a sodium silicate content tends to passivate individual surfaces, particularly those made of aluminum. Sodium carbonate can be used, but the required pH cannot be achieved with it, so that additional pH adjustment with alkali hydroxide is required. It is therefore most expedient to use alkali hydroxide, in particular sodium and / or potassium hydroxide, for the entire pH adjustment. The amount of the hydroxides is generally at least 10 g / l, but is below 80 g / l. If the concentration is too high, there is a risk that the solution will vigorously etch the zinc and aluminum surface and fail to provide the desired coating.
Als Komplexbildner kann jede Verbindung eingesetzt werden, die in der Lage ist, die geforderten Mengen an dreiwertigem Chromat in Lösung zu halten. Obgleich es hierfür eine große Zahl von Verbindungen gibt, werden die besten Ergebnisse erzielt, wenn entsprechend vorteilhafter Weiterbildungen der Erfindung die Metalloberflächen mit einer Lösung in Kontakt gebracht werden, die als Komplexbildner für ChromIII Hydroxicarbonsäure, insbesondere Glukonsäure und/oder Hexahydroxiheptansäure, wie Glucoheptansäure, oder aber als Komplexbildner für ChromIII Aminocarbonsäure, insbesondere Nitrilotriessigsäure und/oder Äthylendiamintetraessigsäure, enthält. Als Hydroxicarbonsäure ist, wenn auch weniger vorteilhaft, Zitronensäure geeignet. Die vorgenannten Säuren können auch in Form ihrer Natriumsalze in die Lösung eingebracht werden.Any compound capable of keeping the required amounts of trivalent chromate in solution can be used as the complexing agent. Although there are a large number of compounds for this, the best results are achieved if, in accordance with advantageous developments of the invention, the metal surfaces are brought into contact with a solution which is used as a complexing agent for chromium III hydroxycarboxylic acid, in particular gluconic acid and / or hexahydroxy heptanoic acid, such as glucoheptanoic acid, or but contains as a complexing agent for ChromIII aminocarboxylic acid, in particular nitrilotriacetic acid and / or ethylenediaminetetraacetic acid. Citric acid is suitable as the hydroxy carboxylic acid, albeit less advantageously. The aforementioned acids can also be introduced into the solution in the form of their sodium salts.
Die Verwendung von Aminocarbonsäure, insbesondere in Verbindung mit Hydroxicarbonsäure, weist den Vorteil auf, daß die Wirksamkeit des Verfahrens erhöht wird, indem ein gleichmäßigerer Beizangriff auf die Metalloberfläche und die Ausbildung eines besonders gleichmäßigen Konversionsüberzuges erfolgt.The use of aminocarboxylic acid, especially in combination with hydroxycarboxylic acid, has the advantage that the effectiveness of the method is increased by a more uniform pickling attack on the metal surface and the formation of a particularly uniform conversion coating.
Damit die erforderliche Konzentration an dreiwertigem Chrom in der Lösung aufrecht erhalten wird, ist es im allgemeinen erforderlich, den Komplexbildner in einer Menge zu verwenden, die oberhalb der theoretisch erforderlichen Menge liegt. Daher werden die Metalloberflächen entsprechend weiterer bevorzugter Ausgestaltungen der Erfindung mit einer Lösung in Kontakt gebracht, die die Hydroxicarbonsäure in einer Menge von 0,2 bis 10 g/l, bzw. die Aminocarbonsäure in einer Menge von 0,5 bis 10 g/l enthält. Die vorgenannten Mengenangaben beziehen sich jeweils auf die neutralen Natriumsalze.In order to maintain the required concentration of trivalent chromium in the solution, it is generally necessary to use the complexing agent in an amount which is above the amount theoretically required. Therefore, according to further preferred embodiments of the invention, the metal surfaces are brought into contact with a solution which contains the hydroxycarboxylic acid in an amount of 0.2 to 10 g / l or the aminocarboxylic acid in an amount of 0.5 to 10 g / l . The aforementioned quantities refer to the neutral sodium salts.
Die zur Durchführung des erfindungsgemäßen Verfahrens benötigte Lösung kann durch Auflösen der einzelnen Bestandteile in Wasser unter Einstellung der jeweils erforderlichen Konzentrationen hergestellt werden. Es ist jedoch auch möglich, die Behandlungslösung durch Verdünnen eines Konzentrates, daß das dreiwertige Chrom, das sechswertige Chrom und den Komplexbildner enthält, in Wasser herzustellen. Dabei kann das zur pH-Wert-Einstellung erforderliche Alkali separat zugegeben werden oder bereits im Ansatzkonzentrat enthalten sein. Geeignete Konzentrate haben üblicherweise einen Feststoffgehalt von 15 bis 40 Gew.-%, insbesondere von 25 bis 35 Gew.-%. Sie enthalten die wirksamen Lösungsbestandteile in dem Verhältnis, in dem sie auch in der arbeitenden Lösung enthalten sind. Dadurch ist es möglich, die arbeitende Lösung durch bloße Verdünnung mit der geeigneten Wassermenge herzustellen.The solution required to carry out the method according to the invention can be prepared by dissolving the individual constituents in water while adjusting the concentrations required in each case. However, it is also possible to prepare the treatment solution by diluting a concentrate that contains the trivalent chromium, the hexavalent chromium and the complexing agent in water. The alkali required for pH adjustment can be added separately or already contained in the batch concentrate. Suitable concentrates usually have a solids content of 15 to 40% by weight, in particular 25 to 35% by weight. They contain the effective solution components in the ratio in which they are also contained in the working solution. This makes it possible to prepare the working solution by simply diluting it with the appropriate amount of water.
Das erfindungsgemäße Verfahren kann auf jede bekannte Weise angewendet werden, die Behandlung der Metalloberflächen im Spritzen oder im Tauchen ist bevorzugt. Die Behandlungsdauer kann sehr kurz sein, beispielsweise 5 bis 15 s betragen, jedoch sind auch längere Behandlungszeiten, beispielsweise bis zu 1 Minute, möglich. Letzteres gilt insbesondere dann, wenn die Konzentration an dreiwertigem Chrom und/oder die Behandlungstemperaturen vergleichsweise niedrig sind. Die Temperatur der mit der Metalloberfläche in Kontakt zu bringenden Lösung liegt normalerweise unterhalb 70°C, im allgemeinen im Bereich von 40 bis 60°C. Die zu behandelnden Werkstücke befinden sich im allgemeinen auf einer Temperatur von 30 bis 50°C, meist bei etwa 40°C vor der Behandlung.The method according to the invention can be applied in any known manner, the treatment of the metal surfaces in spraying or immersion is preferred. The treatment time can be very short, for example 5 to 15 s, but longer treatment times, for example up to 1 minute, are also possible. The latter applies in particular when the concentration of trivalent chromium and / or the treatment temperatures are comparatively low. The temperature of the solution to be brought into contact with the metal surface is normally below 70 ° C, generally in the range of 40 to 60 ° C. The workpieces to be treated are generally at a temperature of 30 to 50 ° C, usually at about 40 ° C before treatment.
Der mit dem erfindungsgemäßen Verfahren gebildete Konversionsüberzug wird in der Regel mit Wasser gespült, im allgemeinen durch Spritzen. Weiterhin ist es vorteilhaft, im Anschluß an die Aufbringung des Konversionsüberzuges eine Passivierungspülung mit einer Chromatlösung, vorzugsweise wie in der GB-PS 1 084 478 beschrieben, vorzunehmen. Daran anschließend erfolgt die Trocknung.The conversion coating formed by the process according to the invention is generally rinsed with water, generally by spraying. Furthermore, it is advantageous to carry out a passivation rinse with a chromate solution, preferably as described in GB-PS 1 084 478, following the application of the conversion coating. This is followed by drying.
Die mit dem erfindungsgemäßen Verfahren erzeugten Konversionsüberzüge weisen einen guten Korrosionswiderstand auf. Sie können ohne weitere Nachbehandlung bleiben, generell ist es jedoch üblich, anschließend einen Lack aufzubringen, der sowohl farblos als auch farbig sein kann.The conversion coatings produced with the method according to the invention have good corrosion resistance. You can stay without further post-treatment, but in general it is common to apply a varnish afterwards, which can be both colorless and colored.
Das erfindungsgemäße Verfahren ist mit Vorteil auf die Behandlung von Zink, Aluminium und deren Legierungen mit anderen Metallen oder untereinander anwendbar. Insbesondere ist die Erfindung von Vorteil, wenn beabsichtigt ist, unterschiedliche Metalloberflächen gleichzeitig oder aber in der Folge zu behandeln. So kann schmelztauchverzinktes oder mit einer Zink/Aluminium-Legierung schmelztauchbeschichtetes Stahlband behandelt werden, ohne daß Änderungen hinsichtlich der Beschaffenheit der Lösung vorgenommen werden müssen.The method according to the invention is advantageously applicable to the treatment of zinc, aluminum and their alloys with other metals or with one another. The invention is particularly advantageous if the intention is to treat different metal surfaces simultaneously or subsequently. For example, hot-dip galvanized or hot-dip galvanized steel strip can be treated without having to change the nature of the solution.
Das erfindungsgemäße Verfahren wird anhand der folgenden Beispiele beispielsweise und näher erläutert.The process according to the invention is explained, for example and in more detail, using the following examples.
Es wurde eine Lösung hergestellt, die folgende Bestandteile enthielt:
Die vorgenannte Lösung wurde im Spritzen bei 50°C für die Dauer von 15 sec. auf Stahlband aufgespritzt, das schmelztauchverzinkt bzw. mit einer Zink/Aluminium-Legierung schmelztauchbeschichtet war. Die Legierung bestand aus 5 Gew.-% Aluminium und 95 Gew.-% Zink. Im Anschluß an die Konversionsbehandlung wurde mit Wasser im Spritzen gespült und getrocknet. Alsdann wurde ein Epoxyprimer und ein Decklack aus einem silikonmodifiziertem Polyester aufgebracht. Das auf diese Weise behandelte Stahlband wurde im Salzsprühtest gemäß ASTM-B 117 für die Dauer von 1500 h behandelt. Die anschließende Bewertung zeigte, daß ausgehend vom Gitterschnitt eine Lackunterwanderung <1 mm stattgefunden hatte.The aforementioned solution was sprayed on at 50 ° C. for 15 seconds onto steel strip which was hot-dip galvanized or hot-dip coated with a zinc / aluminum alloy. The alloy consisted of 5% by weight aluminum and 95% by weight zinc. Following the conversion treatment, it was rinsed with water in a syringe and dried. An epoxy primer and a top coat made of a silicone-modified polyester were then applied. The steel strip treated in this way was treated in the salt spray test in accordance with ASTM-B 117 for a period of 1500 h. The subsequent evaluation showed that, based on the cross-cut, the paint had infiltrated <1 mm.
Es wurde ein Konzentrat hergestellt, das
enthält, hergestellt.A concentrate was made that
contains, manufactured.
Eine arbeitende Lösung kann aus dem vorgenannten Konzentrat durch Verdünnung mit Wasser im Verhältnis 1:10 hergestellt werden.A working solution can be prepared from the aforementioned concentrate by dilution with water in a ratio of 1:10.
Claims (10)
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB888802788A GB8802788D0 (en) | 1988-02-08 | 1988-02-08 | Composition & process for treating metal surfaces |
| GB8802788 | 1988-02-08 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0328908A1 EP0328908A1 (en) | 1989-08-23 |
| EP0328908B1 true EP0328908B1 (en) | 1992-03-04 |
Family
ID=10631278
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP89101302A Expired - Lifetime EP0328908B1 (en) | 1988-02-08 | 1989-01-26 | Process for applying conversion coatings |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US4963198A (en) |
| EP (1) | EP0328908B1 (en) |
| JP (1) | JPH01283386A (en) |
| AU (1) | AU614024B2 (en) |
| DE (2) | DE58900881D1 (en) |
| ES (1) | ES2031288T3 (en) |
| GB (1) | GB8802788D0 (en) |
| NZ (1) | NZ227807A (en) |
Families Citing this family (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5223028A (en) * | 1991-08-19 | 1993-06-29 | Lexmark International, Inc. | Waterfast aqueous inks |
| JPH11106944A (en) * | 1997-10-07 | 1999-04-20 | Nippon Parkerizing Co Ltd | Production of galvanized steel sheet excellent in blackening resistance and resistance against white rust |
| US6461449B1 (en) | 1997-10-07 | 2002-10-08 | Henkel Corporation | Conversion coating zinciferous surfaces to resist blackening and white rust |
| EP1032100B1 (en) | 1999-02-25 | 2002-10-02 | Ngk Spark Plug Co., Ltd | Glow plug and spark plug, and manufacturing method therefor |
| US6663700B1 (en) * | 2000-10-31 | 2003-12-16 | The United States Of America As Represented By The Secretary Of The Navy | Post-treatment for metal coated substrates |
| US6375726B1 (en) | 2000-10-31 | 2002-04-23 | The United States Of America As Represented By The Secretary Of The Navy | Corrosion resistant coatings for aluminum and aluminum alloys |
| US6527841B2 (en) * | 2000-10-31 | 2003-03-04 | The United States Of America As Represented By The Secretary Of The Navy | Post-treatment for metal coated substrates |
| US6669764B1 (en) * | 2000-10-31 | 2003-12-30 | The United States Of America As Represented By The Secretary Of The Navy | Pretreatment for aluminum and aluminum alloys |
| US6511532B2 (en) * | 2000-10-31 | 2003-01-28 | The United States Of America As Represented By The Secretary Of The Navy | Post-treatment for anodized aluminum |
| US6521029B1 (en) * | 2000-10-31 | 2003-02-18 | The United States Of America As Represented By The Secretary Of The Navy | Pretreatment for aluminum and aluminum alloys |
| DE102005059748B4 (en) * | 2005-06-15 | 2020-03-19 | Continental Teves Ag & Co. Ohg | Process for the compression of anodized aluminum workpieces |
| WO2007095517A1 (en) * | 2006-02-14 | 2007-08-23 | Henkel Kommanditgesellschaft Auf Aktien | Composition and processes of a dry-in-place trivalent chromium corrosion-resistant coating for use on metal surfaces |
| CN101448975B (en) * | 2006-05-10 | 2011-07-27 | 汉高股份及两合公司 | Improved trivalent chromium-containing composition for use in corrosion resistant coating on metal surfaces |
| KR100872479B1 (en) | 2007-03-27 | 2008-12-15 | (주)하나나노텍 | Trivalent chromate solution, trivalent chromate-treated metal body and preparation method thereof |
| US10156016B2 (en) | 2013-03-15 | 2018-12-18 | Henkel Ag & Co. Kgaa | Trivalent chromium-containing composition for aluminum and aluminum alloys |
| JP6396563B1 (en) * | 2017-10-10 | 2018-09-26 | 奥野製薬工業株式会社 | Surface treatment liquid |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB441088A (en) * | 1934-07-13 | 1936-01-13 | Pyrene Co Ltd | Improvements relating to the production of protective or paintholding coatings on aluminium or aluminium alloys |
| US2911332A (en) * | 1956-05-25 | 1959-11-03 | Kelsey Hayes Co | Process of coating metal and resulting articles |
| GB869395A (en) * | 1959-05-27 | 1961-05-31 | Pyrene Co Ltd | Improvements relating to the production of chemical coatings on zinc and zinc alloys |
| BE635940A (en) * | 1962-08-15 | |||
| SE316668B (en) * | 1963-09-23 | 1969-10-27 | Parker Ste Continentale | |
| US3935035A (en) * | 1973-06-05 | 1976-01-27 | Nippon Steel Corporation | Aqueous solution and method for surface treatment of metals |
| GB8608508D0 (en) * | 1986-04-08 | 1986-05-14 | Pyrene Chemical Services Ltd | Coating metal surfaces |
-
1988
- 1988-02-08 GB GB888802788A patent/GB8802788D0/en active Pending
-
1989
- 1989-01-26 DE DE8989101302T patent/DE58900881D1/en not_active Expired - Lifetime
- 1989-01-26 EP EP89101302A patent/EP0328908B1/en not_active Expired - Lifetime
- 1989-01-26 ES ES198989101302T patent/ES2031288T3/en not_active Expired - Lifetime
- 1989-01-26 DE DE3902266A patent/DE3902266A1/en not_active Withdrawn
- 1989-01-31 NZ NZ227807A patent/NZ227807A/en unknown
- 1989-02-03 JP JP1024094A patent/JPH01283386A/en active Pending
- 1989-02-07 US US07/307,730 patent/US4963198A/en not_active Expired - Fee Related
- 1989-02-07 AU AU29691/89A patent/AU614024B2/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| ES2031288T3 (en) | 1992-12-01 |
| GB8802788D0 (en) | 1988-03-09 |
| AU614024B2 (en) | 1991-08-15 |
| AU2969189A (en) | 1989-08-10 |
| DE3902266A1 (en) | 1989-08-17 |
| JPH01283386A (en) | 1989-11-14 |
| DE58900881D1 (en) | 1992-04-09 |
| EP0328908A1 (en) | 1989-08-23 |
| NZ227807A (en) | 1991-08-27 |
| US4963198A (en) | 1990-10-16 |
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