Patent Application
20130143071
The invention relates to processes for treating a metallic surface of an object, in particular for treating the metallic surface of an object having a surface composed of an iron material, a zinc material, and/or a tin material, for example composed of zinc and/or a zinc alloy, with an aqueous copper-plating solution for applying a copper layer as a barrier layer and/or as a conductive layer, in particular according to simpler, more cost-effective, and more environmentally friendly methods. However, the object may also be composed of at least one nonmetallic material and/or at least one metallic material that is/are provided with at least one metallic layer.
In metal working, plating refers to the application of a metal layer of a more noble metal to another metal having lower potential, for example by rolling, welding, casting, spraying, and/or dipping, if galvanic processes are used, this is referred to by those skilled in the art as electroplating.
Galvanic treatment is an important technology for protecting and refining metallic and other objects. Galvanic treatment includes any type of electrolytic treatment, i.e., coating and/or treating a metal in an aqueous solution with flow of electrical current. This may involve copper plating, bronze plating, nickel plating, cadmium plating, chrome plating, lead plating, silver plating, rhodium plating, platinum plating, and/or gold plating, for example. In many cases, copper plating, nickel plating, chrome plating, silver plating, and/or gold plating is/are used. Multiple successive galvanic layers often result. Nickel plating may then also be followed by chrome plating, silver plating, platinum plating, rhodium plating, and/or gold plating, for example. Only rarely is there only a single cover layer of copper. Presently, in almost all cases a copper cover layer is followed by at least one nickel cover layer. Presently, in almost all cases a nickel cover layer is followed by at least one other type of cover layer, such as at least one cover layer of gold, platinum, rhodium, silver, or chromium, all cover layers usually being applied electrolytically, and in most cases from acidic aqueous solutions. The cover layers may be, for example, bright copper layers having layer thicknesses typically in the range of 3 to 50 μm and preferably in the range of 5 to 20 μm, thick copper layers having layer thicknesses typically in the range of 50 to 5000 μm and preferably in the range of 80 to 500 μm, bright nickel layers having layer thicknesses typically in the range of 3 to 20 μm, and/or thick nickel layers having layer thicknesses typically in the range of 30 to 250 μm.
If no external power source is used as the supplier of the electrons necessary for the metal deposition, and if this plating is carried out without a content of strong reducing agent, this is referred to by those skilled in the art as electroless plating, coating, or treatment. The addition and use of at least one strong reducing agent for/in the bath without electrical current means that the electrons necessary for the metal deposition are supplied by at least one strong reducing agent present in the bath, in which case this is referred to as chemical or externally electroless plating, coating, or treatment. In addition, the terms “chemical copper” and “chemical nickel” mean that at least one strong reducing agent is used in the bath.
Weak reducing agents are not used in electroplating for the metal deposition, since they do not reach the potential necessary for the deposition, and a chemical (externally electroless) copper bath or a chemical nickel bath does not function with weak reducing agents alone. Therefore, all reducing agents used in chemical copper or nickel baths have a potential with values of −0.8 V maximum or preferably −0.8 V maximum, and particularly preferably −1 V maximum. The information concerning the potential refers to measurements with a standard hydrogen electrode. In addition, these reducing agents are regarded as strong reducing agents; i.e., they have potential values of −0.8 V maximum, often in the range of −3 to −1 V.
Electroless baths are generally preferred over galvanic (electrolytic) baths and/or baths containing the (externally electroless, chemical) strong reducing agent, since they result in more rapid layer formation with less operational effort and with a lower expenditure of energy than for electrolytic, and externally electroless baths, provided that such layers may he provided in an electroless manner at all. However, in many cases the desired metal layers may be produced in a suitable layer quality only electrolytically, for example in an alkaline, cyanidic electrolytic copper plating process, in an alkaline, cyanide-free electrolytic copper plating process, or in an acidic electrolytic nickel strike process. Therefore, present operations are almost always electrolytic, i.e., very energy-intensive and very complicated technically, because no suitable electroless coating processes, and usually also no suitable externally electroless coating processes, are known.
All baths described here and below are aqueous compositions, so that water is not always mentioned for specific compositions. A copper plating bath or nickel plating bath contains the aqueous copper plating solution or nickel plating solution, respectively.
A barrier layer on the surface of a workpiece is often necessary if the workpiece contains a base metal, in order to be able to carry out subsequent processing electrolytically in an aqueous medium. A barrier layer is necessary, for example, to avoid uncontrolled, generally poorly adherent immersion deposition on the workpiece, for example having a surface composed of a metal having a more electronegative potential than copper, from a solution having a higher potential. If a workpiece having a surface composed, for example, of iron, an iron alloy, zinc, and/or a zinc alloy is treated in a sulfuric acid copper sulfate solution which corresponds to the bright layer copper plating or thick layer copper plating of the prior art and is used electrolytically by various electroplating companies, iron, and/or by analogy also zinc, for example, go(es) into solution with release of electrons, according to the redox reaction
Oxidation: Fe→Fe2++2e−
Reduction: Cu2++2e31 →Cu
Metallic copper then deposits on the surface in a non-adherent coating. Since in this manner it has heretofore been possible to deposit only very thin, spongy, porous layers with little or no adhesion, the use of such layers for further processing in the decorative or functional field of electroplating is out of the question.
Thus, without an applied barrier layer, an interfering pickling attack occurs on the clean or cleaned metallic surface, also in acidic electrolytic copper-plating baths. The pickling attack then initiates the immersion deposition. In this regard, in particular iron and/or zinc ions are pickled out of the object to be coated, and go into solution. As a result, electrons are released, which in turn are accepted by the ions of the subsequent acidic galvanic bath. The corresponding metals precipitate as non-adherent cementation on the base material. This pickling attack also sometimes results in destruction of the base material. However, this causes contamination of the subsequent electroplating baths. Introduced foreign substances, optionally including foreign ions, deposit in an uncontrolled manner during the electrolysis, preferably as metal precipitate in the area of low current density. These substances result in dull, gray, streaked, rough, and/or porous layers which are not suitable for further processing, in particular in the technical or decorative field. The foreign substances introduced into the bath may be removed only by selective cleaning, or partially or completely discarding the electroplating bath. If the non-adherent precipitate resulting from the cementation crumbles in the subsequent electroplating baths, for example due to motion of the objects and/or of the bath, the precipitated metal is likewise once again partially introduced into the layer to be deposited, resulting in distinct flaws, pores, roughness, and/or bumps. Such metal crumbs may be removed only by intensive filtering. Basically, when foreign substances are introduced into the subsequent electroplating bath, process disturbances, losses in quality, additional costs, and/or an additional expenditure of effort result, regardless of whether the foreign substances are present as ions, as metallic crumbs, and/or as thin skins.
A barrier layer is used to coat workpieces of any part geometry and made of a base material having low electrochemical potential, such as iron, zinc, tin, and/or their alloys, to avoid pickling attack and destruction of the base material, entrapment of foreign ions into the galvanic bath, contamination of the subsequent baths, immersion deposition, non-adherent, blistered, or porous layers, as well as subsequent coating defects such as dull, gray, or streaked layers.
Barrier layers composed of copper or nickel prior to the further galvanic treatment are basically known. Baths by means of which such barrier layers are produced are also referred to in practice as “strike baths” by those skilled in the art.
Heretofore, for the production of a barrier layer either 1) a cyanidic alkaline electrolytic copper-plating bath, 2) an alkaline electrolytic copper-plating bath containing complexing agent, or 3) an acidic electrolytic nickel strike bath has been used in industrial practice. In approximately more than 85% of cases, a cyanide-containing alkaline electrolytic copper-plating bath 1) is preferentially used in industrial practice in Central Europe. At least one metal coating of a metal having a higher potential than the base material of the original metallic surface may then be directly electrolytically applied to the copper or nickel barrier layer formed in these baths. This may be at least one metal coating and/or at least one alloy coating based on Cu, Ni, Cd, Cr, Ag, Au, Rh, and/or Pt, for example, which is electrolytically applied over a copper plating, nickel plating, cadmium plating, chrome plating, silver plating, gold plating, rhodium plating, and/or platinum plating, in particular from acidic, cyanide-free and reducing agent-free electrolytes, as at least one bright layer and/or as at least one thick layer, for example.
The barrier layers should have excellent adhesion to the base material of the substrate, high ductility, and a high degree of purity, and should be free of pores. However, this does not always occur when foreign substances are present in the bath. In addition, at least one subsequent surface treatment such as electroplating, painting, coating with a powder lacquer or cathodic dip paint (CDP), or joining to another object in each treatment step should be made possible.
A barrier layer according to the invention composed of copper, in addition to the purposes described in general terms above, is used to coat workplaces of any part geometry and also optionally having indentations and recesses, composed of a base material having low electrochemical potential, for example iron and/or zinc and/or their alloys, in high quality in an environmentally friendly, electroless manner, and economically, effectively, and quickly compared to the corresponding process of the prior art.
Presently, when applying a barrier layer and in the prevention of immersion deposition it is therefore still necessary, also prior to further electroplating, to initially electrolytically, i.e., using current, provide workpieces made of a material having a very low potential and in particular to be decoratively or technically refined, with a coating composed of a cyanidic alkaline electrolyte 1), or instead, infrequently a bath 2) containing a purely alkaline complexing agent. Since the metal deposition for 1) is carried out from a metal-cyano complex, or for 2), for example, from a phosphorus complex which has extraordinarily high inner molecular binding forces, immersion deposition during dipping of the part to he coated into the bath is avoided. In this regard, “immersion deposition” is understood to mean uncontrolled electroless deposition of copper, nickel, and/or other metals by electron exchange. This uncontrolled electroless or externally electroless deposition usually results in nonadherent or poorly adherent precipitates which are powdery, porous, gritty (rough, grainy, and removable), and/or granular.
A conductive layer is a layer that is used to increase the inherent electrical conductivity of an object. Thus, for example, a thin copper layer may be applied to a steel wire in order to reduce its contact resistance or line resistance by up to a factor of 20. This is used, for example, for reducing the electrical line resistance in welding wire manufacture, or for reducing the contact resistance in plug-in connections in the electronics sector.
In acidic copper baths, the bath components usually dissociate into the corresponding ions. For this reason, in acidic copper baths a base material having a potential more electronegative than copper cannot be copper-plated either with current or without current, since the more noble metal deposits as liquor in a non-adherent layer on the base material. A copper layer that is deposited in the immersion process is not commercially usable.
In cyanidic alkaline copper baths such as in 1), the copper cyanide complex is stable enough that it does not dissociate into ions. Therefore, a base material having a potential more electronegative than copper cannot be electrolytically copper-plated without current, but may be electrolytically copper-plated in a number of process variants. For this reason, alkaline, cyanidic electrolytic copper baths are usually used at the present time for applying a barrier layer or conductive layer.
These cyanidic alkaline electrolytic processes are operationally reliable and controllable. An electrolytic coating process always requires a higher level of effort than an electroless coating process. Due to the metal deposition with high power consumption and due to the heating of the electrolyte, often to 80° to 85° C., these processes are energy-intensive. Cyanide-containing baths are highly toxic, hazardous, and environmentally unsound. For this reason, they require separate wastewater control and treatment and specific storage conditions. Fatalities in the workplace due to cyanide occasionally occur.
Continuing attempts have been made to replace the highly toxic, hazardous, and environmentally unsound cyanide complex with less harmful complexing agents and complexes for copper-plating baths. Weak complexes such as a citrate, hydroxo, ammonium, acetate, phosphate, or diphosphate complex dissociate in acidic as well as in alkaline solutions. Strong complexes such as ethylenediaminetetraacetate (EDTA) are stable in acidic and in alkaline solutions, but are environmentally unsound due to their hazard to wastewater. For this reason, they are seldom used commercially.
The most important baths and coating processes used in the prior art are described below:
1) Cyanidic alkaline electrolytic copper plating: In more than 85% of cases, in major industrial practice at the present time these barrier layers are usually still applied from cyanidic alkaline copper plating electrolytes, in particular for the base materials iron, zinc, and/or their alloys. Their aqueous compositions and treatment conditions are often as follows:
The copper-plating bath contains approximately 50 g/L CuCN, approximately 75 g/L NaCN. approximately 40 g/L NaOH, and, if necessary, brightening additives, but usually no reducing agent and no acid. The pH of the bath is approximately 12. Operations are carried out at approximately 40° C. and with a current density of approximately 1 A/dm2 for approximately 10 minutes.
Metal deposition occurs according to the following equations:
[Cu(CN)3]2−→[Cu(CN)]+2CN−
[Cu(CN)]+e−(from an external power source, rectifier)→Cu+CN−
However, these types of cyanide-containing alkaline electrolytic copper-plating baths may also be used for altering the technical properties of a base material for certain applications, for example for producing a barrier layer prior to nitriding of steel, or for producing a layer having lower electrical resistance, which is necessary, for example, for conductive heating of workpieces such as screws. This results in the advantages of better corrosion protection and/or better electrical conductivity than the base material itself.
In the cyanide-containing baths, it is also disadvantageous that they are problematic for wastewater, the environment, and disposal due to their toxicity and hazardous nature, that they must be heated to at least 50° C., and that the electrons necessary for the metal deposition must be supplied by an external rectifier, which is energy-intensive.
2) Cyanide-free alkaline electrolytic copper plating: Cyanide-free alkaline baths are not highly toxic. In cyanide-free alkaline copper baths, the bath components usually do not similarly dissociate into the corresponding ions. Therefore, a base material having a potential more electronegative than copper cannot be copper-plated electrolessly; however, it may be copper-plated with current only with difficult process control and after critical pretreatment. For this reason, alkaline cyanide-free electrolytic copper baths are presently used only occasionally for applying a barrier layer. However, the pretreatment of the base material as well as the process control are therefore much more critical or more labor-intensive than for 1). In addition, it has not been possible heretofore to treat all base materials in this manner. Extreme care must be taken in pretreating the workpieces.
These aqueous compositions and treatment conditions are often as follows: The copper-plating bath contains approximately 15 g/L Cu, approximately 50 g/L pyrophosphate, diluted KOH or H3PO4 for adjusting the pH to approximately 9, if necessary, and brightening additives, if necessary. In some cases, the bath may be free of reducing agent, free of pickling agent, and/or free of acid. The bath is used at a temperature of at least 60° C. and with a current density of approximately 1 A/dm2 for approximately 10 minutes.
In the cyanide-free alkaline baths containing complexing agent, it is disadvantageous that process control of the baths is very critical, that the bath parameters must be maintained within very narrow limits, that pretreatment of the baths must be carried out carefully, and that introduction of foreign substances is critical. If foreign substances are introduced as an impurity into the bath, they deposit in the layer to be deposited and impair the quality of this layer. These barrier layers may then be streaked, gray, dull, and/or porous, and are no longer necessarily closed, finely crystalline, pore-free, ductile, and well-adhering. The only remedy may be to discard pad or all of the bath and replenish the bath. In addition, parts made of die-cast zinc cannot be electroplated in the drum plating process due to their poor conductivity, and can be electroplated only in the complicated rack process. Furthermore, these baths must once again be temperature-controlled to at least 60° C. The electrons necessary for the metal deposition are likewise supplied by an external rectifier, which is energy-intensive.
3) Electrolytic galvanic nickel strike bath: For workplaces made of iron and/or its alloys, so-called nickel strike baths are also presently used for applying a harrier layer.
Infrequently, in approximately 3% of cases, nickel strike baths are presently used for barrier layers in industrial practice, in particular for the base materials iron or its alloys. Their aqueous compositions and treatment conditions are often as follows:
In addition to at least one nickel compound, nickel strike baths always contain acid, and often at least one brightener. The baths optionally contain NaCl, for example, as a pickling promoter and/or brightening additives, if necessary. The baths are usually free of caustic solutions and reducing agents. Depending on the base material, they often operate at concentrations of 200 to 250 g/L NiCl2 and approximately 200 g/L HCl at pH levels less than 0.5, or at concentrations of 200 to 250 g/L NiCl2 and approximately 40 g/L H3BO4 at pH levels of approximately 4, at approximately 40° C. for approximately 5 minutes.
In such nickel strike baths, it is disadvantageous that the very high proportion of chloride results in a strong pickling attack on the base material, whereby embrittlement of the base material is difficult to avoid, and sometimes may even result in destruction of the base material. In addition, the strong corrosive effect of the chlorides acts on the entire unit and the entire building. The alternative sulfamate strike baths, which are used only in isolated cases, slightly reduce the high level of corrosion in the surroundings of the baths due to the lower chloride content, but cannot completely prevent the corrosion. In addition, if is absolutely necessary to draw out the gases above the baths due to the possibility of chlorine gas formation. On account of the entrained foreign substances, possibly including foreign ions, the baths must be continuously cleaned, for example by filtering, to remove foreign substances such as metal particles. Foreign substances are introduced by the pickling attack on the base material, in this regard, these baths are also operated intermittently at electrical currents lower than required for depositing the noble metal, in order to deposit the dissolved foreign substances, including foreign ions, on the object to be coated and thus clean the bath. Alternatively, a contaminated bath must be discarded.
4) With acidic bright copper plating or thick copper plating, although it is not possible to produce a barrier layer, such platings are used to form high-quality copper layers; for quite some time, these platings have been used in electroplating, in particular for producing decorative and/or galvanoplastic coatings. However, workpieces made of a base material having a potential more electronegative than copper and without a barrier layer cannot be treated, due to the immersion deposition which occurs therein.
Bright nickel plating can occur only electrolytically in an acid bath. Cost-effective bright copper plating can occur only electrolytically in an acid bath. A cyanidic alkaline electrolytic copper plating 1) could be used as a much less cost-effective alternative. However, the objects that are copper-plated in this way must be subsequently polished by band or machine to achieve the necessary brightness. As an even less cost-effective alternative, a cyanide-free alkaline copper-plating bath 2) containing complexing agent could be used, for which the objects likewise have to be subsequently polished. Lastly, a chemical copper plating would be even less cost-effective due to the high operating temperature required, the high costs for the ultrapure chemicals required, the disposal problem, critical handling, and process control for these chemicals, the very slow deposition rate, and the low degree of ductility and brightness of the copper layers.
Cost-effective thick copper plating or thick nickel plating can occur only electrolytically in an acid bath. As a much less cost-effective alternative, chemical thick nickel plating could be used, which, however, requires a much slower deposition rate, very long treatment times, and very high costs for the complicated wastewater treatment and for the ultrapure chemicals required.
For workpieces coated with an electrolytically produced barrier layer, better corrosion protection, better electrical conductivity, and/or layers with better esthetic and visual appeal than the base material itself result. Further advantages of acidic electrolytic copper baths are ductile, finely porous coatings with high brightness which have good covering power and metal distribution, in addition to the high deposition rate and high efficiency. Therefore, when a barrier layer is present, on materials having a baser potential they are greatly preferred over the alkaline cyanide-free copper-plating baths containing complexing agent, and/or the cyanidic copper-plating baths and/or nickel strike baths.
Such bright copper platings still have the disadvantage that base materials made of metals and alloys having a potential more electronegative than copper, for example iron, steel, zinc, tin, or die-cast zinc, cannot be directly coated in these baths, since they must be provided with a barrier layer beforehand.
In all four of the variants described above, it is disadvantageous that current is necessary for applying the required barrier layer according to one of the variants 1) through 3), and subsequently for the metal deposition in the bright copper bath or thick copper hath 4): depending on the process, application, and base material, a current density of approximately 0.5 to 5 A/dm2, in exceptional cases even up to 50 A/dm2, is used. For a bright nickel bath or thick nickel bath, the current density is usually approximately 2 to 5 A/dm2. For cadmium plating, chrome plating, silver plating, gold plating, rhodium plating, and/or platinum plating which is often additionally used, the current density is approximately in the range of 1 to 10 A/dm2, depending on the process. In addition, treatment times between 5 and 30 minutes are necessary in each case. Therefore, these barrier layers as described under variants 1) through 3) are produced according to a comparatively complicated, energy-intensive, and slow process which is also often very environmentally unsound.
The following procedure is still commonly used at the present time for the galvanic treatment in particular of steel, zinc, and/or zinc die casting parts:
a) Hot degreasing in an aqueous solution of 10 g/L NaOH, 30 g/L sodium pyrophosphate, and 5 g/L wetting agent at 60-95° C. for 5-10minutes,
b) Cascade rinsing in deionized water,
c) Pickling according to the application and base material:
d) Cascade rinsing in deionized water,
e) Electrolytic degreasing with cathodic switching of the object: 10 g/L KOH, 30 g/L sodium silicate, 10 g/L pyrophosphate, and 1 g/L wetting agent at 0.5-2 A/dm2, 1-5 V, and 15-60° C. for 0.5-5 minutes,
f) Cascade rinsing in deionized water,
g) Cyanidic copper plating in aqueous solution at 0.3-1.5 A/dm2, 1-3 V, 60° C., current efficiency η of 70%, and maximum 0.3 μm/min for 5-15 minutes, with:
h) Cascade rinsing in deionized water.
All types of workplaces and also all base materials based on iron, zinc materials, and/or tin may be copper-plated using this treatment procedure.
As a rule, these strike copper-plated workplaces are subsequently acidically bright copper-plated or acidically thick copper-plated. A bright copper plating usually has a layer thickness in the range of 5 to 50 μm. It may be applied electrolytically in a suitable quality, but not without current in industrial practice. A thick copper plating may have a layer thickness in the range of greater than 50 μm to approximately 5 mm, but under certain circumstances may require several weeks of electrolytic or externally electroless (chemical) copper deposition. Occasionally, workpieces having a complicated geometry of the part to be treated are treated once again in an intermediate electroless dipping bath, as in DE 20 28 898 A1, for example, in order to subsequently apply a bright layer or thick layer following an electrolytic cyanidic copper plating. However, even in the plating baths described in the cited document, a strong complexing agent such as cyanide, gluconate, or ethylenediaminetetraacetate (EDTA), having corresponding environmental, toxicity, wastewater treatment, and processing problems, is necessary. Examples of such complexing agents are amines and carboxylic acids, for example gluconic acid, lactic acid, tartaric acid, and their derivatives, such as sodium gluconate, and Rochelle salts, ethylenediamine, diethylenetriamine, diethanol glyoxime, ethylenedsaminetetraacetic acid, lactonitrile, ethylenedinitrilotetraacetic acid (EDTA), hydroxyethyl ethylenediaminetriacetic acid (HEDTA), diethylenetrinitrilopentaacetic acid (DTPA), nitrilotriacetic acid (NTA), triethanolamine, tetrakis(2-hydroxypropyl)ethylenediamine (THPED), pentahydroxypropyldiethylenetriamine, and their derivatives. Wastewater treatment of these substances is very problematic. An electroless dipping bath or also an externally electroless coating bath could be an alternative to an electrolytic electroplating bath. A copper-plating solution, in particular for forming a barrier layer, should preferably be free of strong complexing agents or free of complexing agents, and free of toxic constituents, without external electrical power for metal deposition and bath heating, and without problematic wastewater treatment.
DE 20 28 898 A1 teaches a production procedure as follows:
In comparison, in the present invention the process steps a), b), and c) are replaced by electroless cyanide-free copper plating.
Since the precipitates obtained in the electroless dipping bath described in DE 20 28 893 A1 are still relatively porous, and since in the alkaline pH range the electrolytes known heretofore are very sensitive to insufficient part cleaning and bath impurities, and since for adhesion purposes an additional galvanic alkaline, cyanidic, or some other type of alkaline preliminary bath as a strike bath is still necessary, and an improvement over treatment in a cyanidic electrolytic copper bath without intermediate dipping bath treatment is found only for parts having heavy part geometries, the dipping baths described in the cited document have not found widespread use. For this reason, there is little or no description of electroless dipping baths in reference works and textbooks.
If no additional reducing agent has been added to the solution, electroless metal deposition occurs by cementation or by immersion deposition. The deposition principle is based on the electromotive series of metals, whereby the electrons necessary for the reduction and the associated deposition are supplied by the more noble metal to the less noble metal by an oxidation process.
As may be inferred from N. Kanani, Kupferschichten: Abscheidung, Eigenschaften, Anwendungen [Copper Layers; Deposition, Properties, Applications], Eugen-G.-Leuze-Verlag, Bad Saulgau 2000, pp. 73-74, it has not been possible heretofore to directly provide workpieces made of the base materials iron, zinc, and/or their alloys with a copper coating from an acidic bright copper bath and/or thick layer copper bath. Therefore, it is presently still necessary to provide workpieces made, for example, of the base materials iron, zinc, and/or their alloys with a barrier layer so that contact between the bath solution and the workpiece may be avoided. For this purpose, either 1) a cyanidic alkaline electrolytic copper-plating bath, 2) an alkaline electrolytic copper-plating bath containing complexing agent, or 3) an acidic electrolytic nickel strike bath is usually used, depending on the base material.
Without a barrier layer, an acid bath such as an acidic copper plating bath or nickel plating bath will exert an interfering pickling attack on the clean or cleaned metallic surface based on iron and/or zinc, in which case immersion deposition always occurs when a less noble metal is dipped into the solution of a more noble metal, since in particular iron and/or zinc ions are then pickled out of the object to be coated and go into solution, thereby releasing electrons, which are then once again accepted by the ions of the acid galvanic bath, resulting in immersion deposition.
The aim of any galvanic treatment (i.e., using current) is to electrolytically apply a cover layer to the metallic object preferably from an acidic aqueous solution, since compared to an alkaline electrolyte, the acidic electrolyte offers significant advantages with regard to deposition rate, brightness, metal distribution, covering power, porosity, and efficiency. Acidic electrolytes are also less sensitive to impurities, and more stable in use than cyanide-free alkaline electrolytes. Hence, alkaline electrolytes often result in a number of disadvantages.
For this reason, cyanide-free alkaline galvanic processes are used only rarely, for example when the number of baths, for example due to space reasons, is not sufficient for the design for an acidic galvanic treatment. These baths then operate at ph levels greater than 10, wherein numerous disadvantages are accepted, such as brightness level, sensitivity to impurities and foreign substances, slower deposition, and less favorable metal distribution, depending on the current density, and accordingly, less favorable throwing power. However, on metallic surfaces, in particular of iron and zinc materials, such an acidic aqueous solution requires a barrier layer so that the acidic aqueous solution does not accept interfering impurities, ions, and electrons from the metallic substrate, and so as not to impair the electrolytic deposition process and the quality of the galvanic cover layer.
DE 39 14 180 C2 discloses compositions of electroless, chemical copper baths based on copper sulfate and cyanide which operate at a pH of at least 9.5 and which are supplied with electrons, necessary for the metal deposition, from a reducing agent, usually formaldehyde. In addition, this bath contains strong complexing agents such as EDTA and/or cyanide.
DE 15 21 200 A1 describes alkaline externally electroless nickel baths which operate at a pH of at least 8.5 and which obtain electrons, necessary for the metal deposition, from the reducing agent sodium hypophosphite. In addition, these baths contain stabilizers such as sodium citrate and/or ammonium chloride.
U.S. Pat. No. 3,715,793 discloses thick nickel films produced externally electrolessly and in a cyanide-free manner, which are deposited from solutions having a pH of 3.5 or 7.5 to 9 at approximately 55° to 95° C. or having a pH of 7.5 to 10 at 40° to 95° C.
In these externally electroless processes, it is disadvantageous that all metallic objects and also the foreign substances in the bath are continuously coated as long as they are present in the bath. Purely chemical, i.e., externally electroless, copper baths and nickel baths, which make the metal deposition possible with the aid of a strong reducing agent, have not become widespread in practice due to the required working temperature, the very high costs of the necessary ultrapure chemicals, the wastewater and disposal problems and the critical handling and process control of these chemicals, the low ductility and brightness level, and the very slow deposition rate.
Heretofore, a workpiece made of iron materials, including steels and stainless steels, could be acidically copper-plated without current in an adhesive manner and with layers that are usable for further processing only if at least one strong reducing agent such as hypophosphite and/or pyrophosphate was added to the bath, and/or if a barrier layer was deposited beforehand from a cyanidic alkaline electrolytic copper bath, a cyanide-free alkaline electrolytic copper bath containing complexing agent, or an acidic nickel strike bath.
Heretofore, a workpiece made of zinc materials could not be acidically copper-plated without current, or acidically or alkalinically nickel-plated without current, in an adhesive manner and with layers that are usable for further processing unless at least one strong reducing agent such as hypophosphite and/or pyrophosphite was added to the bath, and/or unless a copper barrier layer was deposited beforehand from a cyanidic alkaline electrolytic bath or from a cyanide-free alkaline electrolytic bath containing complexing agent.
Heretofore, a workpiece made of iron or zinc materials could not be alkalinically copper-plated without current, or alkalinically nickel-plated without current, in an adhesive manner and with layers that are usable for further processing unless least one strong reducing agent such as hypophosphite and/or pyrophosphite was added to the bath.
EP 1 495 157 B1 teaches an aqueous, freeze- and thaw-stable concentrate for copper plating based on basic copper carbonate and complexing agent(s).
U.S. Pat. No. 4,563,216, concerns aqueous compositions for the electroless coppering of iron-based materials on the base of 10 to 30 g/L Cu(II), 1 to 10 g/LCl−, 0.1 to 10 g/L of aminopolyacetic acid and either (i) 0.01 to 10 g/L of acriflavine hydrochloride and 0.1 to 20 g/L of polyalkylene oxide C12 -C18-alkyl or -alkenyl amine or (ii) 0.1 to 10 g/L of the reaction product of ortho-toluidine and formaldehyde.
GB 0 927 576 A teaches the coating of metallic surfaces of stronger electronegativity as copper with solutions on the base of copper salt and ethyleneoxide condensate of a long-chain aliphatic amine.
U.S. Pat. No. 2,217,921 refers to an acidic copper containing solution on the base of Cl, Br or F comprising acid, of pickling inhibitor for iron-based materials and 7.088 to 56.7 g per gallon or 1.56 to 12.46 g Cu per liter. U.S. Pat. No. 3,536,129 describes an electroless process for coppering of iron-based materials on the base of 0.1 to 1% by weight of Cu.1 to 3 % by weight of Cl and 0.1 to 1 g/L acridine compound.
DE 1965641 A discloses a two-step process, in which first a solution is used on the base of non-oxidizing mineral acid and 20 to 100 g/L of soluble Ti salt, optionally a fluorotitanate salt, and in which then a conventional copper containing solution with an ortho-toluidine-formaldehyde condensation product or with ethylenediaminetetraacetic acid is used for electroless coppering or for electroless copper-tin-coating on surfaces of stainless steel.
U.S. Pat. No. 3,640,343 protects the electroless coppering of iron-based materials with solutions of a pH less than 2 on the base of copper comprising sulfate, alkaline organic N-containing inhibitor, a water-soluble chloride salt and a strong mineral acid.
U.S. Pat. No. 5,776,231 concerns in the same way like EP 0 711 848 A1 a solid concentrate on the base of copper sulfate pentahydrate and water-free magnesium sulfate as well as a process for the electroless coppering.
WO 02/053801 A2 teaches a continuous process for wire drawing on the base of acidic solutions of copper, bromide, inhibitor and water-soluble lubricant.
U.S. Pat. No. 3,793,037 concerns an acidic aqueous solution for electroless coppering on the base of copper, halogenide, polyalkylene glycol and tertiary amine.
The object is to propose a process in which a barrier layer and/or conductive layer may be applied in particular to iron and zinc materials by copper plating in a simple, cost-effective, environmentally friendly, and more rapid manner.
The object is to propose processes in which cover layers such as bright layers and/or thick layers are electrolytically applied without using a cyanidic alkaline bath, for example a cadmium-plating, copper-plating, nickel-plating, or zinc-plating bath or an externally electroless bath, beforehand for forming a barrier layer before the electrolytic cover layer(s) is/are formed.
A further object is to propose processes which are as cost-effective, rapid, high-qualify, and environmentally friendly as possible, in this regard if would be preferable to propose processes which are easily and reliably usable on a broad scale.
It has now surprisingly been found that electroless copper plating is also easily possible on iron, zinc, and/or tin workpieces, including workpieces made of steels and stainless steels, using a simple process and with high quality of the barrier layer to be formed. This process is surprisingly simple, cost-effective, operationally reliable, rapid, environmentally friendly, and nontoxic. The process may even be used without added reducing agents.
The object is achieved using a process for treating a metallic surface of an object with an aqueous copper-plating solution, characterized in that a first copper-plating solution, which is free of cyanide and free of strong reducing agent, measured with a standard hydrogen electrode, having a potential with values less than −0.6 V, and which contains no complexing agent with the exception of ions which are dissolved and/or pickled out of the surfaces, is electrolessly used on clean metallic surfaces of the object, or after a pretreatment, to cleaned metallic surfaces, wherein a first copper layer or copper alloy layer is formed as a barrier layer and/or as a conductive layer, and the object which is provided with an electrolessly produced copper layer is galvanically treated at least once, painted at least once, or coated at least once with a powder lacquer or with a cathodic dip paint (CDP), or is joined to another object.
In particular, metallic surfaces of iron, zinc, tin, and/or their alloys may be copper-plated using the process according to the invention. An object made of an iron material, zinc, and/or a zinc alloy is preferably treated,
A first copper-plating solution is preferably used electrolessly in a cyanide-free manner to form a barrier layer and/or a conductive layer on a metallic surface less noble than copper. Using the copper-plating solution according to the invention, i.e., using the copper-plating bath according to the invention, for a suitable chemical composition of the bath, i.e., having a content of at least one alloying element such as zinc and/or tin, a copper alloy layer may also be formed. For the sake of simplicity, in the discussion below only a copper layer and copper plating are referred to, even if a copper alloy layer is formed. In this sense, references, for example, to “nickel” include nickel and nickel with alloying elements in the baths, as well as nickel and nickel alloys in the layers.
In one particularly preferred embodiment, an object made of an iron material, zinc, a zinc alloy, and/or a tin material is treated, provided that the first copper-plating solution in the treatment of an object made of iron or steel, optionally with the exception of stainless steel, contains no complexing agent. This is because a weak complexing agent is particularly advantageous for the copper plating of stainless steel.
The object is further achieved using an object having a barrier layer and/or a conductive layer which is/are produced according to the invention. The barrier layer and/or conductive layer is/are preferably completely pore-free.
At least one galvanic cover layer based, for example, on copper, nickel, or one of their alloys is also optionally electrolytically applied to the electrolessly applied barrier layer and/or conductive layer.
In particular, this involves the use of a process for treating a metallic surface of an object with an aqueous copper-plating solution according to the invention and/or objects coated according to the invention for electrolessly forming a first copper layer or copper alloy layer as a barrier layer and/or as a conductive layer, primarily on surfaces of iron materials, zinc materials, and/or tin.
The copper-plating solution used according to the invention may thus be kept free of strong complexing agents, for example complexing agents and/or complexes based on cyanide, diethylenetriamine, diethanol glyoxime, ethylenediamine, ethylenediaminetetraacetic acid, hydroxyethyl ethylenediaminetriacetic acid (HEDTA), diethylenetrinitrilopentaacetic acid (DTPA), gluconic acid, lactonitrile, nitrilotriacetic acid (NTA), Rochelle salts, triethanolamine, tetrakis(2-hydroxypropyl)ethylenediamine (THPED), pentahydroxypropyldiethylenetriamine, and their derivatives, in particular free of ethylenediaminetetraacetate (EDTA), having corresponding environmental, toxicity, wastewater treatment, and/or processing problems.
The copper-plating solution used according to the invention is preferably also free of weak complexing agents, for example complexing agents and/or complexes based on lactic acid, acetic add, tartaric acid, citric acid, and their derivatives and mixtures. In contrast, an environmentally friendly weak complexing agent, for example based on citric acid, lactic acid, acetic acid, tartaric acid, and/or their derivatives, does not have an interfering effect, either in copper-plating solutions according to the invention or in the disposal of residues of the copper-plating solution. Adding citric acid and/or one of its derivatives, for example a citrate such as sodium citrate, potassium citrate, and/or ammonium citrate, may be advantageous in particular for metallic surfaces, for example composed of stainless steel, that are difficult to copper-plate, in particular with a content in the bath in the range of 0.1 to 120 g/L, 1 to 80 g/L, 3 to 60 g/L, 6 to 35 g/L, or 12 to 20 g/L.
However, the copper-plating solution used according to the invention may also be kept free of strong reducing agents, since these are also environmentally unsound and hazardous to wastewater, and sometimes also toxic, and because complexing agents and strong reducing agents require additional treatment in wastewater. The first copper-plating solution preferably contains no intentionally added complexing agent, and particularly preferably contains no complexing agent.
Since Sn2+ ions have a potential of −0.14 V, Fe2+ ions have a potential of −0.44 V, and Zn2+ ions have a potential of −0.76 V, based on measurements with a standard hydrogen electrode, and although these ions likewise have a reducing effect, among other things, in the present context they are not regarded as reducing agents as defined. For differentiation from weaker reducing agents having a low potential, for example in the range of +0.2 V or 0 V, i.e., comparatively large voltage values, according to this definition the strong reducing agents should have a potential of −0.6 V or even lower negative voltage values, for example values in the range of −0.8 to −1.8 V. Therefore, either no reducing agents, or no strong reducing agents, are added to the copper-plating solution according to the invention. Rather, the ions pickled or dissolved out of the metallic surface, for example Fe2+, Sn2+, Zn2+, and/or other ions, for example from alloy components and/or from other metallic materials of the treated metallic surface, which often have values in the range of −0.1 to −3 V, likewise act as a reducing agent. Therefore, the process according to the invention requires a content of these types of ions which are also necessarily obtained by pickling or dissolving out of the metallic surface and which have a reducing effect. For this reason, the copper-plating solution according to the invention requires no strong reducing agent, and in particular no reducing agent at all, which is intentionally added to the copper-plating solution. The first copper-plating solution preferably contains no added reducing agent and no strong complexing agent, with the exception of the ions which are dissolved and/or pickled out of the surfaces.
The ions which are pickled or dissolved out of the metallic surface, for example Fe2+, Sn2+, Zn2+, and/or other ions, are used as the system's own reducing agent. This is because the surface of the iron material, for example, is pickled, so that the pickled-out or dissolved-out iron ions, for example, may act as a reducing agent. Therefore, the copper-plating bath according to the invention which is used electrolessly operates in its solution, at least immediately after the first contact with a base metal or material containing ions such as Fe2+. For iron-containing surfaces, operations are preferably carried out at a pH less than 5, preferably less than 3, particularly preferably less than 2, or less than 1, to allow a pickling attack on the metallic surface. For surfaces of zinc and/or other base metals, operations are preferably carried out in a weakly acidic, neutral, or alkaline range. In that case, zinc also does not go into solution by pickling out of the zinc surface. The pH for zinc-rich surfaces is preferably at least 4, since otherwise zinc would be pickled, and this could easily result in destruction of the base material. This is because the pickling attack on zinc is several times stronger than for iron. For pH values in the range of 4 to 8 and in particular 6.5 to 8, zinc-rich surfaces may be satisfactorily processed, whereby zinc goes into solution due to the difference in potential between zinc and copper, and not due to the pickling attack. The zinc ions thus dissolved, and/or ions of other base metals which are/have been pickled and/or dissolved out, apparently act as the system's own reducing agent. It is therefore not necessary to add reducing agent. The minimum potential of the system's own reducing agent for iron is −0.44 V, and for zinc is −0.76 V, as measured with a standard hydrogen electrode. The first copper-plating solution preferably contains ions having potential values in the range of −0.1 to −2.5 V, or −0.4 to −2 V.
In the process according to the invention, the barrier layer and/or conductive layer produced according to the invention may also be applied to iron and zinc materials, including stainless steel, as well as to tin, in a simple, cost-effective, environmentally friendly, and more rapid manner than in processes of the prior art. This process preferably has no complicated additional process steps such as required electropolishing or required electrolytic degreasing.
If necessary, the following steps may be required prior to the copper plating according to the invention:
1. Alkaline or pH-neutral hot degreasing to remove, for example, residues of grease, oil, dust, etc., followed by rinsing with water.
2. Activation of the in particular oxidically contaminated metallic surface, for example by acidic, or less frequently, also alkaline, pickling, and/or by mechanical machining such as lapping, grinding, or blasting, and by subsequent rinsing with water. In the case of alkaline pickling, or if any type of such an activation step is dispensed with, pickling with a highly diluted, slightly acidic aqueous liquid is common.
A pickling attack of the subsequent acidic galvanic bath on the base material is avoided by means of the barrier layer according to the invention, since the copper barrier layer is not attacked, or is not significantly attacked, by the subsequent galvanic bath. The copper barrier layer and/or copper conductive layer according to the invention is/are composed either only of copper or essentially of copper, and optionally a small amount of alloy components for copper, optionally a small amount of brighteners or other additives, and/or a small amount of other components additionally introduced into the layer from the copper-plating solution.
The copper-plating solutions used according to the invention for electroless formation of a barrier layer and/or conductive layer are aqueous compositions which may vary over a broad range with regard to their concentrations and additives. The copper-plating solutions contain at least one copper compound such as a copper sulfate hydrate. The copper content of the copper-plating solution as a bath solution may be approximately in the range of 0.5 to 120 g/L Cu, preferably in the range of 1 to 100, or 2 to 80, or 5 to 60, or 7 to 40, or 9 to 25, or 11 to 18 g/L Cu. In contrast, the other additives to the copper-plating solution used according to the invention may vary greatly, so that no other type of additive necessarily has to be added in any bath. The copper-plating solution may in each case, if necessary, contain at least one pickling agent, pickling inhibitor, pickling promoter, chelate, chelate-forming agent, brightener, complex, weak and/or strong complexing agent, wetting agent, buffer substance, weak reducing agent, acid, floating agent for the pH, and/or optionally other additives. The copper-plating solution preferably contains ions, in particular pickled-out and/or dissolved-out ions, such as Fe2+, Zn2+, and/or other ions, which are/have been pickled and/or dissolved out of alloy components and/or of other metallic materials of the treated metallic surface and which have potential values in the range of −0.4 to −1.8 V. The total content of solids and active substances in the copper-plating solution as a bath solution is often in the range of 1 to 400 g/L, preferably in the range of 2 to 300, or 5 to 250, or 10 to 200, or 20 to 150, or 30 to 125, or 40 to 100, or 60 to 80 g/L. The highest contents usually have the at least one copper compound and optionally also at least one acid and/or at least one weak complexing agent.
It has been found that the pickled-out and/or dissolved-out ions, in particular Fe2+, Sn2+, and Zn2+, have the same effect as added strong reducing agents. It has been determined that the pickled-out and/or dissolved-out ions are necessary for the process according to the invention if no strong reducing agent is added. Even at the start of operations, it is usually not necessary to add such ions to the bath, since the copper plating begins on metallic surfaces even without addition of Fe2+, Sn2+, and Zn2+, for example, so that when the object to be treated, made of base metallic material, is dipped, ions are automatically released into the typically acidic or neutral copper-plating solution and then act as a reducing agent. In particular ions of relatively base metals such as Fe2+ and/or Zn2+ may act as the system's own reducing agent.
The copper-plating solution according to the invention may contain acids, for example sulfuric acid, hydrochloric acid, nitric acid, and/or hydrofluoric acid, as pickling agent, in particular in quantities in the range of 0.1 to 200 g/L, particularly preferably 5 to 130 g/L or 50 to 80 g/L, in each case. The total acid content is preferably in the range of 0.1 to 400 g/L, or 10 to 200 g/L, or 30 to 130 g/L.
As pickling inhibitor, an amine such as tributylamine, or butinediol, cyclohexanol, nitrobenzenesulfonic acid, propinol, putindiol [sic], and/or one of their derivatives may be added to the copper-plating solution according to the invention. For acidic solutions, at least one alkali halide such as sodium chloride and/or sodium fluoride is often preferably used as pickling promoter.
Complexing agents such as citric acid and its derivatives, as well as chemically related carboxylic acids and their derivatives, are regarded as weak complexing agents in the field of electroplating. In many compositions for electroless copper plating, addition of complexing agent is not necessary. It is often necessary to add no complexing agent, since this is favorable for wastewater treatment due to the fact that even weak complexing agents may dissolve salts such as nickel, and cause environmental damage. The stronger a complexing agent that is contained in the bath, the higher the possible level of necessary effort for wastewater treatment. The copper-plating solution according to the invention is preferably free of strong complexing agents such as cyanides, amines, carboxylic acids, and their derivatives, since these compounds result in corresponding environmental, toxicity, wastewater treatment, and/or processing problems. In many embodiments, strong complexing agents are preferably not intentionally added. Examples of such complexing agents include gluconic acid, lactic acid, tartaric acid, and their derivatives, such as sodium gluconate, and Rochelle salts, ethylenediamine, diethyienelhamine, diethanol glyoxime, ethylenediaminetetraacetic acid, lactonitrile, ethylenediaminetetraacetic acid (EDTA), hydroxyethyl ethylenediaminetriacetic acid (HEDTA), diethylenetrinitrilopentaacetic acid (DTPA), nitrilotriacetic acid (NTA), triethanolamine, tetrakis(2-hydroxypropyl)ethylenediamine (THPED), pentahydroxypropyldiethylenetriamine, and their derivatives.
However, a subsequent electrolytic cover layer does not have to be produced with an electrolyte that is free of strong complexing agents, regardless of their composition or a content of Ag, Cu, Ni, and/or Cr, for example.
For example, ethylenedinitrilotetraacetic acid (EDTA), triazole, ascorbic acid, porphin, heme, chlorophyll, and/or their derivatives, and in particular ethylenedinitrilotetraacetic acid dinitrate, dialkylaminoethyltolyltriazole, and/or sodium ascorbate, may be used as chelate-forming agents or corresponding chelates in the copper-plating solution according to the invention. The total content of chelate-forming agents and/or corresponding chelates in the copper-plating solution according to the invention is preferably in the range of 0.001 to 100 g/L, particularly preferably in the range of 0.1 to 20 g/L or 0.5 to 5 g/L.
As brightener, for example at least one compound based on alkylsulfonic acids, amines, for example products of reaction with propylamines, and based on benzenesulfonic acids, coumarines, esters of (meth)acrylic acids, and based on melilotic acid, saccharines, sulfonamines, sulfonimides, and/or sulfinic acids may be added to the copper-plating solution according to the invention.
As wetting agent, for example polyhydric alcohols, ether compounds, ethoxylates, carboxylates, sulfonates, sulfates, quaternary ammonium compounds, ethane compounds, surfactants, and/or their derivatives may be used in the copper-plating solution according to the invention. The total content of wetting agents in the copper-plating solution according to the invention is preferably in the range of 0.001 to 100 g/L, particularly preferably in the range of 0.1 to 20 g/L or 0.5 to 5 g/L.
As buffer substances, for example boric acid, ammonia, carbonic acid, acetic acid, sodium carbonate, amines, aminomethane, sulfonic acids, citric acid, acetates, borates, ammonium compounds, and/or their derivatives may be used in the copper-plating solution according to the invention. The total content of buffer substances in the copper-plating solution according to the invention is preferably in the range of 0.001 to 100 g/L, particularly preferably in the range of 0.1 to 20 g/L or 0.5 to 5 g/L.
As floating agent, for example acids and caustic solutions and/or their derivatives may be used in the copper-plating solution according to the invention. The total content of floating agents in the copper-plating solution according to the invention is preferably in the range of 0.001 to 100 g/L, particularly preferably in the range of 0.1 to 20 g/L or 0.5 to 5 g/L.
For electroless formation of the barrier layer and/or conductive layer, the copper-plating solution according to the invention preferably contains at least one copper compound and at least one brightener, at least one acid, and/or at least one pickling agent. In addition, the copper-plating solution according to the invention particularly preferably contains at least one pickling inhibitor and optionally also a pickling promoter. Alternatively or additionally, the copper-plating solution according to the invention may particularly preferably contain at least one brightener.
The copper-plating solution according to the invention is free of intentionally added strong reducing agent, i.e., free of reducing agent having potential values of −0.6 V at most, and in particular values in the range of −3 to −1 V.
If is preferred to keep the copper-plating solution according to the invention free or essentially free of stabilizers for the copper-plating solution having an organic and/or inorganic basis. Diethylenetriaminepentaacetic acid, phosphonic acid, thioglycolic acid, thiourea, and/or their derivatives, for example, may be used as organic stabilizers. Compounds based on cadmium, lead, vanadium, and/or mercury, for example, may be used as inorganic stabilizers. These types of stabilizers are usually not easily biodegradable. The organic stabilizers may leach the heavy metals from sediments and possibly result in transport of the heavy metals into surface water, while the inorganic stabilizers are toxic and environmentally unsound. It is generally preferred to keep the copper-plating solution according to the invention free or essentially free of toxic heavy metal ions.
The pH of the copper-plating solution according to the invention is preferably adjusted to the materials of the metallic surfaces which are to be copper-plated. When the pH of the copper-plating solution according to the invention is low, a pickling attack occurs on an iron material such as sheet metal. As a result, Fe2+ is pickled out and goes into solution, thus releasing electrons which are accepted by the copper, leading to precipitation of metallic copper. For the copper plating of metals which are baser than iron, for example, and for their alloys, the pH of the copper-plating solution is often preferably in a range of approximately 4 to 8 or 5 to 8. For the copper plating of zinc or zinc-containing alloys, the pH of the copper-plating solution is particularly preferably in a range of 4.5 to 7 or 8 to 7.5. For iron-rich workpieces, the pH of the copper-plating solution is particularly preferably in the range of 0 to 2, and for zinc-rich workpieces is particularly preferably in the range of 4.5 to 7.5 or 8.5 to 7. For zinc-rich or tin-rich metallic surfaces, the pH of the first copper-plating solution is particularly preferably in the range of 4.5 to 3.5or 8 to 8, or for iron-rich metallic surfaces, is less than 5.
The electroless copper plating according to the invention and/or subsequent electrolytic coating may be carried out by dipping, spraying, rolling, brushing, pouring, sponge application, pad application, and/or in other similar ways. Dipping is usually performed. Electroless coating and/or subsequent electrolytic coating is preferably carried out by dipping, spraying, rolling, brushing, pouring, sponge application, and/or pad application. The object which is provided with a barrier layer and/or conductive layer preferably undergoes at least one subsequent surface treatment.
For successful electroless copper plating, it is important to ensure that the metallic surfaces for the electroless copper plating are metallically bright and free of grease. It is likewise important that the copper concentration in the copper-plating solution, the bath temperature, the treatment time, the pickling inhibitor content, and/or the brightener content of the copper-plating solution are coordinated with one another.
The temperature at which the electroless copper plating according to the invention is carried out is preferably in the range of 15° to 95° C., particularly preferably in the range of 20° to 35° C. or 30° to 70° C. If copper plating is carried out at temperatures above 50° C., a much shorter treatment time results. However, if operations are conducted at higher temperatures, if should be ensured that the concentration and/or the treatment time is/are not excessively great in order to avoid spongy, poorly adherent layers. On the other hand, copper plating may also be carried out at temperatures below 50° C., in which case sufficiently high concentrations and/or sufficiently long treatment times should be ensured in order to avoid porous copper layers, and thus, the inadequate barrier effect of the barrier layer or the insufficient conductivity of the conductive layer, as well as contamination of the bath and problems in subsequent process steps. Operation at room temperature is likewise possible if a sufficient concentration of the copper solution and/or a sufficient treatment time is/are ensured,
Electroless copper plating is preferably carried out over a period in the range of 0.05 to 30 minutes, 0.2 to 10 minutes, or preferably 0.5 to 2 minutes, in order to form a copper layer according to the invention as a barrier layer and/or as a conductive layer. If the bath has a lower concentration than, for example, 0.5 g/L copper in the copper-plating solution, a higher bath temperature and/or a longer treatment time must be ensured. If the copper-plating bath has a higher concentration than, for example, 100 g/L Cu in the copper-plating solution, a lower bath temperature, shorter treatment time, higher pickling inhibitor content, and/or higher brightener content must be ensured. However, if the copper concentration in the bath, the bath temperature, the treatment time, the pickling inhibitor content, and/or the brightener content in the copper-plating solution are not coordinated with one another, either porous copper layers or spongy, poorly adherent copper layers are formed. In the electroless copper plating according to the invention, a copper layer thickness in the range of, for example, 0.1 to 8 μm or in the range of 1 to 5 μm preferably forms, in particular within a period of 0.5 to 2 minutes.
Electroless copper plating allows much more rapid copper plating than with current, or by externally electroless copper plating with the aid of a reducing agent, and also results in much greater energy savings. This is because the time savings for electroless deposition is approximately 20 to 90% compared to electrolytic or externally electroless deposition. The energy savings for electroless deposition are approximately 90 to 100% compared to electrolytic deposition. For electroless deposition, the energy savings are approximately 40 to 70% compared to externally electroless chemical deposition, since chemical copper deposition is very slow, and must always be carried out above 60° C., sometimes above 90° C. This is because the copper-plating solution becomes unstable at high copper concentrations, which may also result in formation of spongy, poorly adherent copper layers.
In addition, better corrosion protection and/or better electrical conductivity than for the base material itself advantageously result(s).
If necessary, additional electrolytic copper plating and/or additional electrolytic nickel plating may be carried out on the at least one copper layer electrolessly produced according to the invention, for example to apply in each case at least one bright copper layer, thick copper layer, bright nickel layer, or thick nickel layer. After formation of the barrier layer and/or conductive layer, at least one cover layer is preferably electrolytically applied as a galvanic bright layer, or at least one layer is preferably chemically or electrolytically applied as a thick layer. These coatings may be high-quality, but are particularly complicated to produce. Chemical thick layers are advantageous in particular for workpieces having difficult shapes, since they have uniform layer thicknesses, regardless of the workplace geometry. This is because the current intensity is nonuniformly distributed for workpieces having holes, cavities, edges, etc., and results in different layer thicknesses which are proportional to the current intensity. To these layers, in each case at least one electrolytic silver, chromium, gold, cadmium, platinum, and/or rhodium layer may additionally be applied if necessary, in particular from acidic electrolytes that are free of cyanide and free of reducing agent, for example as at least one bright layer and/or as at least one thick layer.
After application of the barrier layer and/or the conductive layer, the object which is provided with an electrolessly produced copper layer may be galvanic-ally treated at least once, may be painted at least once, may be coated at least once with at least one powder lacquer or with at least one cathodic dip paint (COP), and/or may be joined to at least one other object. The joining may be carried out, for example, by gluing, clinching, and/or rolling under pressure, optionally also at elevated temperature. The object which is provided with an electrolessly produced copper layer is preferably electroplated at least once, painted at least once, or coated at least once with a powder lacquer or with a cathodic dip paint (CDP), or is joined to another object.
It has been found that surfaces of iron, steel, zinc, and zinc alloys may be satisfactorily copper-plated using the process according to the invention. For example, zinc die casting alloys such as ZnAlMg and ZnAlMgCu alloys (ZAMAK alloys) may also be satisfactorily electrolessly copper-plated according to the invention.
In some cases, if has not been possible to carry out copper plating with zinc alloys having a very inhomogeneous structure or heavy surface contamination, for example if aluminum pockets in the alloy have prevented deposition due to the difference in potential between Al and Zn, for example. This problem may be eliminated in these situations by first carrying out electrolytic zinc plating, rinsing with water, and subsequently carrying out electroless copper plating according to the invention.
The electroless copper plating of stainless steel surfaces according to the invention is more difficult than for steel surfaces, in particular due to the natural oxide skin on the stainless steel surfaces. Stainless steel surfaces have been successfully copper-plated in numerous tests in which for the pickling, at least one nonoxidizing acid has been used for the prior activation, and in which for the electroless copper plating, in addition an electrically conductive contact of a metal that is baser than stainless steel, such as aluminum, aluminum alloy, low-alloy iron and steel materials, zinc, and/or zinc alloy, with the stainless steel surface is used, for example via a contact wire. In the process according to the invention, stainless steel surfaces are electrolessly copper-plated, wherein for the pickling, prior to the copper plating at least one nonoxidizing acid is used for the prior activation, and for the copper plating, in addition an electrically conductive contact of a metal that is baser than stainless steel with the stainless steel surface is used, if necessary. This is because stainless steel often behaves differently than other iron and steel materials, and frequently cannot be easily pickled in sulfuric acid. According to the previous state of knowledge, an electrically conductive contact with a metal that is baser than stainless steel appears to be necessary for stainless steel surfaces, which have a higher content of steel refining agents such as Cr, Ni, and/or V. For low concentrations of steel refining agents, the degreased and pickled stainless steel surfaces may be satisfactorily copper-plated, even without using an electrically conductive contact with a metal that is baser than stainless steel. Such an electrically conductive contact of a sacrificial metal composed, for example, of aluminum, aluminum alloy, slightly alloyed iron and steel materials, zinc, and/or zinc alloy with a stainless steel surface allows the sacrificial metal in the copper-plating solution to provide electrons for the metal deposition. A pickling attack on the sacrificial metal occurs, and the sacrificial metal goes into solution. The released electrons migrate to the stainless steel surfaces via the electrically conductive contact. The stainless steel surfaces may then also be copper-plated due to a sufficient number of free electrons. For higher-alloy stainless steels, so-called immersion deposition in the dipping process functions only when it is used in the contact and immersion process. For stainless steels having a low content of steel refining agents, the release of electrons appears to be less hindered than for higher-alloy stainless steels. Therefore, for some stainless steel alloys it is possible to successfully copper-plate stainless steel surfaces, even without an electrically conductive contact of the stainless steel surface with a sacrificial metal. For low-alloy stainless steels, so-called immersion deposition thus functions in the dipping process, even when it is used in the immersion process. The qualify of the copper plating is not adversely affected as a result. For the contact and immersion process and the dipping process, the bath contents and the thermal conditions for copper-plating stainless steel surfaces are practically the same as for the copper plating of steel surfaces.
It has also been found that fin surfaces may also be copper-plated according to the invention. The bath contents and the thermal conditions for copper-plating tin surfaces are practically the same as for the copper plating of zinc surfaces.
It has now surprisingly been found that, using the products Gardobond® CU 7600 and Gardobond® CU 7602 from Chemetall GmbH, Frankfurt am Main, high-quality copper barrier layers may easily be electrolessly applied in particular to the materials iron, steel, zinc, tin, and even die-cast zinc in an environmentally friendly manner. These products allow a high-quality adherent base surface for decorative and/or functional further processing in the field of electrocoating. In some cases, as explained in greater detail in the examples and comparative examples 6 through 9, it is also thus possible to replace extensive electrolytic procedures. The high level of adhesion of the obtained coatings has been verified. In the decorative and/or functional coating of workpieces made of iron, steel, zinc, die-cast zinc, or tin, for example, in the field of electroplating it is thus possible to dispense with electrolytic precopper-plating or electrolytic prenickel-plating for forming a barrier layer, and to replace it with an electroless dipping process in an acid bath.
It has now surprisingly been found that it is possible to apply a barrier layer and/or conductive layer to metallic objects, using a cyanide-free copper-plating solution which is used electrolessly, for example. In this regard it was surprising that if is possible to also subsequently apply an acidic galvanic coating to surfaces of iron- and/or zinc-rich metallic objects or to tin, since heretofore the teaching in the field of surface coating has been that a layer deposited from an acidic copper electrolyte onto an object having a surface based on iron and/or zinc is not suitable for further processing.
In this regard it was surprising that it is possible, even without a subsequent bright copper layer or thick copper layer, to directly apply a subsequent bright nickel layer or thick nickel layer to the copper barrier layer produced according to the invention without losses in quality.
However, it has also surprisingly been found that, for example, barrier layers for nitriding steel, also partially, or layers for increasing the electrical conductivity of a component, likewise selectively on only a portion of the surface, may be produced using the process described in the invention.
Furthermore, it has surprisingly been found that bright copper layers may also be deposited using the process according to the invention, so that in some cases it is even possible to dispense with subsequent acidic bright copper plating or subsequent acidic bright nickel plating and, if necessary, to subsequently directly carry out bright nickel electroplating, bright gold electroplating, bright silver electroplating, and/or bright chrome electroplating, depending on the application.
At least one electrolytic bright nickel layer or electrolytic thick nickel layer may also be directly applied to the barrier layer and/or conductive layer applied according to the invention, without the objects which are provided with a barrier layer having to be additionally coated beforehand with an acidic electrolytic bright copper layer. It is irrelevant whether electroless operations are carried out utilizing a cyanide-containing copper-plating solution or a copper-plating solution used according to the invention. It is also irrelevant whether the barrier layer has been applied on a surface composed, for example, of an iron material, a zinc material, a tin material, and/or a more noble surface.
The object which is coated with a conductive layer produced according to the invention may be used to produce an object having better electrical conductivity, such as a wire, profile, pipe, rod, or object having a complex shape, for conductive heating, and/or for hardening the metallic object.
The object which is coated with a barrier layer and/or conductive layer according to the invention may be used as a wire, profile, pipe, or rod, as welding wire, as a fitting, element, or connecting element for windows, doors, or furniture, for example, such as a roller or a screw, as an element of an apparatus, of a machine, of a household appliance, of an electrical device, of an electronic device, or of a toy, for example as a switch or button, as a decorative object such as a candle holder, as an element for a clock, as a housing, rod assembly, mounting, mounting plate, or covering, as an element in equipment construction, machine construction, automotive manufacture, or for means of transport, as a mechanical functional part or for a metallic object to be hardened, such as a drill, an element in particular in equipment construction, automotive manufacture, machine construction, or tool manufacture which is subject to wear, or as a screw.
The following examples and comparative examples are intended to illustrate the invention by way of example.
A hull cell sheet is a sheet which may be used in a hull cell. The hull cell has a trapezoidal cross section. As a result of the trapezoidal shape of the hull cell in plan view, the distance between the anode and the cathode varies. Therefore, the current density between the cathode and the anode also varies, the highest current density corresponding to the smallest distance between the two electrodes, and the lowest current density corresponding to the largest distance between the two electrodes. However, the current density distribution is not linear, but, rather, increases more rapidly with increasingly smaller distance. It is thus possible to test an electrolyte, such as an acidic bright copper bath, at a single hull cell sheet over a broad current density range that is important for the metal deposition.
The adhesion of the applied layers was tested using cross-cut, wipe, and bending tests according to DIN EN ISO 2409, DIN EN ISO 1519, and ASTM 2794, and by means of these tests was verified as satisfactory for all examples according to the invention.
Two commercially available hull cell sheets made of ST2 steel were subjected to alkaline hot degreasing in 10 g/L NaOH, 30 g/L sodium pyrophosphate, and 5 g/L wetting agent at 70° C. for 3 minutes, thoroughly rinsed with tap water, pickled for 10 seconds in 5% sulfuric acid (briefly for activating the surface), and once again rinsed in tap water. The metallic surfaces were meticulously cleaned in this way. The cleaned sheets were subsequently dipped info an electroless bath to form a barrier layer. The bath of the first copper-plating solution had the following aqueous composition:
Gardobond® CU 7602 is marketed by Chemetall GmbH as a freeze- and thaw-stable, concentrated aqueous solution. The solution of Chemetall GmbH Gardobond® CU 7602 diluted with tap water has an aqueous composition based on basic copper carbonate, weakly basic buffer substance, weak complexing agent, and brightener. The copper-plating solution with added sulfuric acid was used at a temperature of 30° C. and a pH less than 0.5 over a period of 0.5 minutes, followed by rinsing with tap water at room temperature.
A pickling attack on the steel sheet occurred due to the low pH of the electroless bath solution. As a result, Fe2+ was pickled out and went info solution, thus releasing electrons. The electrons were in turn accepted by the copper ions present in the solution. Metallic copper precipitated onto the iron part. The specialized formulation and raw material combination of the Gardobond® CU 7602 product allowed particularly adherent copper barrier layers due to the type of chemical bonding of the layer to the base material.
The sheets coated with a copper barrier layer showed strong adhesion and a distinct gloss, even without a bright copper layer having been applied. The layer thickness of the barrier layer was 1.4-1.5 μm, and was uniformly distributed on the front and back sides of the sheet. The copper barrier layers could not be scratched off, even with the fingernail. The cross-cut adhesion test was passed with a rating of GT0. In addition, bending of the hull cell sheet over 180° was possible without layer chipping at the inner and outer bending edges. The applied barrier layer was extremely ductile, pore-free, and finely crystalline, without internal layer tension.
The sheets were subsequently galvanically bright copper-plated or thick copper-plated in a conventional acidic bright copper bath at 2 A/dm2 and a temperature of 35° C. for 15 minutes, or for thick layers, for 60 minutes. The sheets were then rerinsed with tap water and dried. Bright nickel plating could also have been performed directly on the electrolessly applied copper barrier layer instead of the bright copper plating, in which case the cyanidic copper plating as well as the acidic bright copper plating of the conventional production process could have been dispensed with.
Under varying pretreatment conditions and under varying conditions for forming the barrier layer, such as temperature, concentration, and immersion time, in acidic galvanic bright copper electrolyte the sheets based on Gardobond® CU 7602 showed smooth, high-gloss copper barrier layers having good adhesion over the entire current density range of 0.1 to 20 A/dm2; the good adhesion was verified by cross-cut and bending tests.
The bright copper layer and the thick copper layer were very glossy and showed excellent adhesion. All properties of all the copper layers were of high quality and acceptable. The process proceeded in a particularly rapid, simple, cost-effective manner without a large expenditure of energy and without problems.
If necessary, further electrolytic copper plating, electrolytic nickel plating, or other electrolytic deposition could have been subsequently carried out, and/or colored coatings could have been electrolessly deposited in a chemical manner. In addition, after each of these coatings, paint or adhesive could have been applied instead of further galvanically or electrolessly produced coatings.
Two hull cell sheets made of ST2 steel were pretreated and copper-plated as in example 1, except that an electroless dipping bath treatment was carried out in
Gardobond® CU 7600 is marketed in powdered form by Chemetall GmbH. The aqueous solution of Gardobond® CU 7600 contains copper sulfate hydrate, pickling inhibitor, pickling promoter, and wetting agent. The hull cell sheets were treated at a temperature of 30° C. at a pH<1, in particular at pH values of approximately 0.5, for 0.5 minutes, then rinsed with tap water.
A pickling attack on the steel sheets occurred due to the low pH. As a result, Fe2+ was pickled out and went into solution, thus releasing electrons which were accepted by the copper. Metallic copper then precipitated on the sheet.
The sheets were subsequently galvanically bright copper-plated or thick copper-plated in a conventional acidic bright copper bath at a current density of 2 A/dm2 and a temperature of 35° C. for 15 minutes, or for thick layers, for 60 minutes. The sheets were then rerinsed with tap water and dried. Bright nickel plating could also have been performed directly on this electrolessly applied copper barrier layer instead of the bright copper plating, in which case the cyanidic copper plating as well as the acidic bright copper plating could have been dispensed with.
Under varying pretreatment conditions and under varying conditions for electrolessly forming the barrier layer, such as concentration, temperature, and immersion time, using Gardobond® CU 7600, the sheets showed smooth, high-gloss copper barrier layers having very good adhesion over the entire current density range. The thickness of the applied barrier layer was 1.6-1.7 μm, and was uniformly distributed on the front and back sides of the sheet. The uniformity was verified by cross-cut and bending tests. The copper barrier layers could not be scratched off, even with the fingernail. The cross-cut adhesion test was passed with a rating of GT0. In addition, bending of the hull cell sheet over 180° was possible without layer chipping at the inner and outer bending edges. The applied barrier layer was particularly ductile, pore-free, and finely crystalline, without internal layer tension.
The bright copper layer and the thick copper layer were very glossy and showed excellent adhesion. All properties of alt the copper layers were of high quality and acceptable. The process according to the invention proceeded in a particularly rapid, simple, cost-effective manner without a large expenditure of energy and without problems.
If necessary, further electrolytic copper plating, electrolytic nickel plating, or other electrolytic deposition could have been subsequently carried out, and/or colored coatings could have been electrolessly deposited in a chemical manner. In addition, after each of these coatings, paint or adhesive could have been applied instead of further galvanically or electrolessly produced coatings.
Two additional hull cell sheets were pretreated as in comparative example 1 and subsequently bright copper-plated or thick copper-plated, but without forming a barrier layer in-between in a copper immersion bath. The aim was to demonstrate the great importance of the electroless copper plating and the copper barrier layer, as well as the necessity of a copper barrier layer for the further galvanic treatment.
It was possible to deposit a high-gloss bright copper layer or high-gloss thick copper layer on the cleaned sheets; however, these layers did not show base material adhesion. Distinct blister formation was apparent after the sheets were lifted from the acidic electrolyte. The copper layers flaked off over a large surface area during the subsequent drying with compressed air at 2 bar. The remaining residues of the copper layers could then be scratched off with the fingernail. Therefore, no further coating was carried out. These copper layers were not commercially usable.
Two additional hull cell sheets 4 and 4a were initially pretreated as in comparative example 1. After hot degreasing and rinsing with water, sheet 4a of comparative example 4a was additionally pickled and cathodically degreased in order to replicate the process conventionally used in industry: the second sheet was pickled with 5% sulfuric acid for 30 seconds at room temperature. After the pickling, the sheet was rerinsed in tap water and subsequently electrolytically degreased. The degreasing was carried out cathodically in an aqueous solution of 10 g/L KOH, 30 g/L sodium silicate, 10 g/L pyrophosphate, and 1 g/L wetting agent at 2 A/dm2 and 30° C. for 3 minutes. An additional cleaning effect compared to sheet 4 was thus achieved.
Subsequently, the two cleaned sheets were not subjected to an electroless dipping bath treatment, but, rather, were treated in a galvanic process with a commercially available cyanidic alkaline copper electrolyte of approximately 15 g/L Cu, approximately 50 g/L sodium cyanide, approximately 50 g/L sodium hydroxide solution, wetting agent, brightener, and further additives. The galvanic copper plating for producing a barrier layer was carried out at 1 A/dm2 and 50° C. for 5 minutes. Forming the galvanically produced barrier layer for a given layer thickness required approximately five times as long as for the electroless copper plating of the barrier layer according to the invention.
The sheets coated with a copper barrier layer showed high adhesion; after the cyanidic galvanic copper plating, sheet 4 and sheet 4a showed a dull, nonglossy surface, without a bright copper layer having been applied. The layer thickness of the barrier layers on the side facing the anode was 1.2-2.5 μm, depending on the extended anode distance present in the hull cell. The copper barrier layers could not be scratched off with the fingernail. The cross-cut adhesion test was passed with a rating of GT0. In addition, bending of the hull cell sheet over 180° was possible without layer chipping at the inner and outer bending edges. The applied barrier layer was ductile, almost pore-free, and crystalline, with slight internal layer tensile stress.
The layer thickness of the barrier layers on the back side facing away from the anode, for which it was difficult or impossible for the current field lines to reach, was 0.06 μm and 1.4 μm, depending on the extended anode distance present in the hull cell and the throwing power of the cyanidic galvanic copper-plating bath, but increased toward the outer edges of the sheet. In the middle of the sheet on the back side, there was an area approximately 2.3×1.8 cm in size that had not been coated with copper at all, so that a blank spot was visible. The copper barrier layers also could not be scratched off with the fingernail on the back side.
The sheets were subsequently galvanically bright copper-plated in a conventional acidic bright copper bath at 2 A/dm2 at a temperature of 35° C. for 15 minutes. If was noteworthy that directly after the galvanic bright copper plating of the central area on the back side of the sheet, which previously had not been provided with a cyanidically produced barrier layer, had a dull, gritty, streaked, slightly blackish copper layer. Since no barrier layer was present in this area, a pickling attack occurred at this location on the base material in the acidic bright copper plating bath, which in turn initiated immersion deposition.
The sheets were then rerinsed with tap water and dried. Instead of the bright copper plating, bright nickel plating could have been carried out directly on this cyanidically produced copper barrier layer. Sheet 4treated in this manner exhibited a bright copper layer on the front side which had excellent adhesion. Additionally treated sheet 4a exhibited a high-gloss copper layer on the front side which likewise had excellent adhesion. On the back side of both sheets, the applied bright copper layer likewise exhibited excellent adhesion at the locations where it was possible to previously provide a cyanidically produced copper barrier layer. In the middle area on the back side of the sheet, where no barrier layer could be applied due to the field line distribution of the current, the copper layer resulting at that location flaked off over a large surface area during the subsequent drying with compressed air at 2 bar. The remaining residues of the copper layer in this area could then be easily scratched off with the fingernail. Therefore, no further coating was carried out. This copper layer on the back side of the sheet was not commercially usable. Despite more complex production, sheet 4a showed no advantages compared to sheet 4.
To test the capability of the barrier layers achieved using the pretreatment products Gardobond® CU 7600 and Gardobond® CU 7602from Chemetall GmbH, in order to address the range of parts to be treated in a commercial electroplating facility, and in particular the range of treated alloys, due to the better ease of handling, various sections of various samples from machining steel, structural steel, and spring steel alloys were treated to increase the corrosion protection and/or optical refinement according to the processes for comparative example 1 and example 1, and according to the processes for comparative examples 3, 4, and 4a.
In the treatment according to the invention of the various types of parts according to the processes for example 2, the same high-quality properties and advantages as in example 2 resulted for all parts.
In this regard, after the galvanic treatment in the bright copper electrolyte or thick copper electrolyte, the parts had well-adhering and well-formed high-gloss bright copper layers or high-gloss thick copper layers, respectively. In the pipe inferior, where galvanic coating could not be successfully carried out, uncontrolled cementation during the electroplating process with corresponding layer chipping was prevented by the electroless use of Gardobond® CU 7600 or Gardobond® CU 7602for producing barrier layers. High-gloss, well-adhering copper layers were also found in the pipe interior. The dipping bath was not contaminated.
All properties of all the copper layers were high-quality and acceptable. The process likewise proceeded in a particularly rapid, simple, cost-effective manner without a large expenditure of energy and without problems.
Here as well, for the parts treated according to the process for comparative example 3 a totally inadequate adhesion of the bright copper layer or of the thick copper layer to all alloys was observed. For hollow parts such as pipe sections, which could not be internally reached with current on account of the Faraday cage effect, a very rough, grainy, and gritty non-adherent copper layer was also exhibited. This layer partially loosened during the electroplating process in the electrolyte, thus contaminating the electrolyte.
For the parts treated according to the processes for comparative examples 4 and 4a, this was likewise apparent to a lesser extent, depending on the throwing power of the cyanidic electrolyte and the depth of the part or the geometry or length of the pipe section. At the locations unreachable by current on account of the Faraday cage effect, such as in pipe interiors, it was not possible to produce a barrier layer for treatment in an acidic bright copper bath, also using a cyanidic electrolyte. Upon immersion into the acidic bright electrolyte or thick layer electrolyte, uncontrolled immersion deposition thus once again began at locations without a barrier layer, which in turn resulted in nonadhesion of the layer at these locations, and which heavily contaminated the electrolyte, and which could have contaminated subsequent electroplating baths such as a bright nickel bath. The workpiece sections treated according to comparative example 4 showed a bright, high-gloss copper surface according to comparative example 4a.
In addition, all examples 1, 2, 4, and 4a passed the cross-cut adhesion test with a rating of GT0, provided that this was possible due to the part geometry. Bending of the test part sections over 180°, likewise provided that this was possible due to the part geometry, was also possible without layer chipping at the inner and outer bending edges. Depending on the base material, the applied barrier layer according to comparative example 1 and according to example 2 had a layer thickness between 1.1 and 1.8 μm, regardless of the part geometry, and the copper plating was uniformly distributed over all locations of the parts. The barrier layers were extremely ductile, pore-free, and finely crystalline, without internal layer tension.
The barrier layer applied according to comparative examples 4 and 4a had a layer thickness of 0 μm, depending on the part geometry, at locations where the current necessary for the deposition was not delivered on account of the Faraday cage effect, and therefore, no copper deposition occurred. At electrolytically well-supplied locations, a layer thickness of up to 4.6 μm was deposited, with a nonuniform distribution of the copper plating on the workpieces, depending on the anode distance and the correspondingly increasing current density. In addition, the barrier layers applied according to comparative examples 4and 4a were ductile, almost pore-free, and crystalline, with slight internal layer tensile stress.
For setting certain strength parameters, high-quality steel screws are partially conductively heated and subsequently hardened by quenching. To increase the electrical conductivity, it is therefore necessary to provide the screws with a good electrically conductive copper layer as a conductive layer, which should have a layer thickness in the range of 1 to 5 μm.
Sample parts of these types of screws were treated in the mass production process of such screws according to the prior art, as follows:
All parts treated in this way had a very well-adhering copper layer, with the copper contact of which it was easily possible to carry out conductive heating with low, greatly reduced resistance. The screws treated according to comparative example 6 exhibited a dull copper surface. In addition, bending of the test screws over 90°, provided that this was possible due to the part geometry, was possible without layer chipping at the inner and outer bending edges. The conductive layer galvanically applied from a cyanidic bath was ductile, almost pore-free, and crystalline, with slight infernal layer tensile stress in the copper layer.
The same screws as in comparative example 6 were hot-degreased, rinsed, pickled, rerinsed, and then, without further steps, directly treated electrolessly with the copper-plating bath based on Gardobond® CU 7602 as in example 1, at 30° C. for 0.5 minutes. In contrast to comparative example 6, in the present case rinsing with deionized water, rinsed electrolytic degreasing, and pickling were not carried out. Instead of the cyanidic alkaline electrolytic copper plating, the electroless copper-plating bath of comparative example 1 was used.
Nevertheless, the screws were provided with an adherent, distinctly bright copper layer having a thickness of 1.6 to 1.8 μm. The conductive heating of the copper-plated screws was carried out without problems, since the copper layer had particularly low electrical resistance. The screws treated according to comparative example 7 exhibited a bright copper surface, in addition, bending of the test screws over 90°, provided that this was possible due to the part geometry, was possible without layer chipping at the inner and outer bending edges. The conductive layer applied according to this process was ductile, pore-free, and crystalline, without internal stress.
All properties of oil the copper layers were high-quality and acceptable. The production process proceeded particularly quickly, easily, reliably, and cost-effectively without a large expenditure of energy and without problems, and in a nontoxic and environmentally friendly manner compared to processes of the prior art. In contrast to the cyanidic electrolytic copper layers of the further prior art, the copper layer is completely pore-free, and therefore of higher quality and more electrically conductive.
High-quality screws were treated as in comparative example 7, except that as electroless dipping bath, Gardobond® CU 7600 having a composition as in example 2 was used at 30° C. for 0.5 minutes.
All parts treated in this way exhibited a very well-adhering copper layer with a slight gloss, a thickness of 1.3 to 1.5 μm, and low electrical resistance, the same as for the copper-plated screws in comparative example 7. By use of this copper layer, conductive heating of the screws was possible without problems. In addition, bending of the test screws over 90°, provided that this was possible due to the part geometry, was possible without layer chipping at the inner and outer bending edges. The conductive layer applied according to the process according to the invention was particularly ductile, pore-free, and crystalline, without infernal stress.
All properties of all the copper layers were high-quality and acceptable. The production process proceeded particularly quickly, easily, and cost-effectively without a large expenditure of energy and without problems. The conductive layer could be applied in a particularly reliable, nontoxic, and environmentally friendly manner compared to processes of the prior art. In contrast to the cyanidic electrolytic copper layers of the prior art, the copper layer is pore-free, and therefore of higher quality and more electrically conductive.
Additional screws were treated as under comparative example 6, except that the cyanidic alkaline electrolytic copper plating step was replaced by a cyanide-free and reducing agent-free acidic electrolytic bright copper plating step based on approximately 200 g/L CuSO4×5 H2O, approximately 60 g/L technically pure H2SO4, and approximately 80 mg/L NaCl in addition to further leveling and brightening organic additives, at 2 A/dm2 and a deposition rate of approximately 0.5 μm/min at 30° C. for 5 minutes. The composition was identical to that of the bright copper plating bath used in other examples for further processing to apply a bright copper layer with a barrier layer present.
All parts in comparative example 9 exhibited a high-gloss copper layer which, however, had no adhesion. Conductive heating at low resistance was not possible. Further processing of the screws resulting from comparative example 9 also was not possible, since the deposited copper layers had already peeled off during the drying in a drum. Thus, the required low electrical resistance of the screws for the subsequent hardening by conductive heating to approximately 680° C. could not be achieved. Hardening and quenching of these screws was not possible.
A steel roller was treated as follows:
Further processing of the roller treated according to comparative example 10 was possible without problems. The nickel barrier layer applied using the conventional process generated a very well-adhering base surface for the subsequent thick copper plating. The thick copper plating could not be scratched off, even with the fingernail. The cross-cut adhesion test was passed with a rating of GT0. As an additional load test, the applied thick copper layer of the gravure roller was ground with grain size 1000 using a cylindrical polishing machine from Sanko Kokai, and was subsequently polished to a high gloss. Engraving and gouging of a gravure pattern into the polished thick copper plating was possible without problems. The applied thick copper plating was pore-free and finely crystalline.
A roller was treated as in comparative example 10, except that the strike nickel-plating process of comparative example 10 was replaced by an electroless copper immersion bath treatment based on Gardobond® CU 7602, using a bath operation and a process sequence as in comparative example 1. In addition, after the degreasing and strike copper-plating, rinsing was performed only once, resulting in a 40% reduction in rinse water consumption. For applying the barrier layer, it was possible to reduce the treatment time of the printing roller from 40 minutes, as described in comparative example 10, to 0.5 minutes. The applied copper barrier layer had a layer thickness of 0.8 to 0.9 μm which was uniformly distributed over the entire roller. The applied copper barrier layer was also glossy. It was thus possible to reduce the treatment time by a factor of 80, and to reduce the quantity of metal applied by a factor of 40. This demonstrates that by using this process, a complex, toxic nickel plating process which is common in the industry may be replaced by a copper plating process that is much more environmentally friendly with only limited health hazards, and much easier and quicker.
Further processing of the printing roller treated according to comparative example 11 was possible without problems. The copper barrier layer applied using this process represented an excellent adherent base surface for the subsequent thick copper plating. The thick copper plating could not be scratched off with the fingernail. The cross-cut adhesion test was passed with a rating of GT0. As an additional load test, the applied thick copper layer of the gravure roller was ground with grain size 1000 using a cylindrical polishing machine from Sanko Kokai, and was subsequently polished to a high gloss. Engraving and gouging of a gravure pattern info the polished thick copper plating was possible without problems. The applied thick copper plating was pore-free and finely crystalline.
To retest the adhesion of the coating on the base material, in a test print the printing roller was subsequently turned on a lathe with an advance of 0.1 mm. The applied copper plating layer could be easily turned cut by cut without losing its adhesion.
A roller was treated as in comparative example 10, except that the strike nickel-plating process of comparative example 10 was replaced by an electroless copper immersion bath treatment in Gardobond® CU 7600, using a bath operation as in example 2 and a process sequence as in example 2. In addition, after the degreasing and strike copper-plating, rinsing was performed only once, resulting in a 40% reduction in rinse water consumption. For applying the barrier layer, it was possible to reduce the treatment time of the printing roller from 40 minutes, as described in comparative example 10, to 0.5 minutes. The applied copper barrier layer had a layer thickness of 0.7 to 0.9 μm which was uniformly distributed over the entire roller. The applied copper barrier layer was slightly glossy. If was thus possible to reduce the treatment time by a factor of 80, and to reduce the quantity of metal applied by a factor of 40. This demonstrates that by using the process according to the invention, a complex, toxic nickel plating process which is common in the industry may be replaced by a copper plating process that is much more environmentally friendly with only limited health hazards, and much easier and quicker.
Further processing of the printing roller treated according to comparative example 12 was possible without problems. The copper barrier layer applied using the process according to the invention represented an excellent adherent base surface for the subsequent thick copper plating. The thick copper plating could not be scratched off with the fingernail. The cross-cut adhesion test was passed with a rating of GT0. As an additional load test, the applied thick copper layer of the gravure roller was ground with grain size 1000 using a cylindrical polishing machine from Sanko Kokai, and was subsequently polished to a high gloss. Engraving and gouging of a gravure pattern into the polished thick copper plating was possible without problems. The applied thick copper plating was pore-free and finely crystalline.
To retest the adhesion of the coating on the base material. In a test print this printing roller was subsequently turned on a lathe with an advance of 0.1 mm. The applied copper plating layer could be easily turned cut by cut without losing its adhesion.
Another cylinder was acidically galvanically thick copper-plated directly after the degreasing and rinsing, without applying a pre-layer such as a barrier layer, corresponding to comparative example 3.
Since there was no barrier layer, uncontrolled immersion deposition began upon immersion into the acidic thick copper plating electrolyte, so that the layer did not adhere, and heavily contaminated the electrolyte. The copper layer partially peeled off during the coating. Further processing of the treated printing roller was therefore not possible.
Various zinc die casting parts such as push knobs, buttons, switches, window fittings, and modelmaking items composed of various zinc alloys such as ZL0400, ZL0410, or ZL0430 were subjected to the treatment described below in order to address the range of parts, and in particular the range of alloys, to be treated in a commercial electroplating facility:
The applied barrier layer had a layer thickness between 0.3 and 0.4 μm, regardless of the part geometry, with the copper plating uniformly distributed over the workpiece surfaces. The barrier layers were very ductile, pore-free, and finely crystalline, without infernal layer tension. The zinc die casting parts coated with the copper barrier layer showed high adhesion and a distinctly bright surface, without a bright copper layer having been applied. The copper barrier layers could not be scratched off with the fingernail. The cross-cut adhesion test was passed with a rating of GT0. Bending of the parts over 90° was possible without layer chipping at the inner and outer bending edges.
The zinc die casting parts were subsequently galvanically bright copper-plated in a conventional acidic bright copper bath at 2 A/dm2 at a temperature of 35° C. for 15 minutes. The zinc die casting parts, which had previously been provided with the barrier layer, showed a high-gloss bright copper layer having excellent adhesion, as verified by cross-cut and bending tests.
By using tap water instead of the deionized water required in the conventionally used cyanidic galvanic copper plating process, it was also possible to reduce the rinse water costs by more than 60% by using this process.
In the treatment of the various types of parts according to the process for comparative example 14, the same high-quality properties as in comparative example 1 resulted for all parts.
All properties of all the copper layers were high-quality and acceptable. The processes proceeded particularly quickly, easily, and cost-effectively, without a large expenditure of energy and without problems. In addition, pickling attack and immersion deposition on the base material as a result of the acidic bright copper bath were avoided.
The same types of zinc die casting parts were treated as in comparative example 14, except that the electroless copper plating in the dipping bath was omitted without replacement, so that no barrier layer was formed.
These zinc die casting parts exhibited no deposited copper layer after the bright copper plating process. Since no barrier layer was present, the metallic surface pickled intensely during the electroplating in the acidic bright copper electrolyte, which made metal deposition for the galvanic copper plating impossible. In addition, all workpieces were destroyed by the very strong pickling. The introduction of foreign zinc ions into the electrolyte resulted in impairment, and ultimately destruction, of the bright copper electrolyte.
The same types of zinc die casting parts as in comparative example 14 were coated, except that the electroless dipping bath treatment was replaced by a conventional alkaline cyanidic copper plating process at 1 A/dm2 and 55° C. for 5 minutes in order to replicate the production process for zinc die casting parts according to the prior art.
The applied barrier layer had a layer thickness between 0 and 3.9 μm, depending on the part geometry, with a nonuniform distribution of the copper plating on the workpiece surfaces, depending on the anode distance and the correspondingly increasing current density. There was no copper deposition at locations which, on account of the Faraday cage effect, were unreachable by the current necessary for depositing copper from cyanidic galvanic electrolyte. In addition, the applied barrier layers were ductile, almost pore-free, and crystalline, with slight infernal layer tensile stress. The zinc die casting parts coated with a copper barrier layer showed high adhesion, but after the cyanidic galvanic copper plating had a dull, nonglossy surface since no bright copper layer had been applied. The copper barrier layers could not be scratched off with the fingernail. The cross-cut adhesion test was passed with a rating of GT0. Sending of the parts over 90° was possible without layer chipping at the inner and outer bending edges.
The zinc die casting parts were subsequently galvanically bright copper-plated in a conventional acidic bright copper bath at 2 A/dm2 at a temperature of 35° C. for 15 minutes. It was noteworthy that at locations that had not been provided with a copper barrier layer due to the pad geometry and the Faraday cage, gassing began immediately after immersion into the galvanic bright copper plating bath. At these locations a pickling attack occurred on the base material due to the acidic solution of the bright copper bath, resulting in destruction of the base material. After a higher throughput, the introduction of foreign zinc ions resulted in destruction of the acidic bright copper bath. The zinc die casting parts, which had previously been provided with a copper barrier layer, showed a high-gloss copper layer having excellent adhesion. This was verified by cross-cut and bending tests.
By using deionized water instead of the more favorable tap water used in the process with Gardobond® GU 7602, it was possible here as well to deposit high-gloss, defect-free bright copper layers having excellent adhesion.
This procedure is also more burdensome, and, due to the greater number of process steps, much longer electroplating times, and greatly increased expenditure of energy, is much more resource-intensive than a procedure according to the invention.
Zinc-coated sheet steel sections were treated according to the processes as in comparative examples 14 through 16.
It was shown that excellent results could be easily and quickly achieved using a composition based on the Gardobond® CU 7602 product in an electroless process: the copper layers were adherent, distinctly bright, and very well suited for further processing.
However, if a cyanidic electrolytic copper plating according to the prior art was used instead (comparative example 17a), this environmentally unsound, toxic process involving an increased level of effort resulted in good copper plating having copper layers that were adherent, dull, and satisfactory for further processing.
The adhesion of the applied layers was tested using cross-cut, wipe, and bending tests according to DIN EN ISO 2409, DIN EN ISO 1519, and ASTM 2794. The coatings from comparative examples 17 and 17a showed good adhesion.
For the electrolytic use of an acidic bright copper bath (comparative example 17b), due to the low pH of approximately 1 a pickling attack occurred on the zinc plating, which was completely dissolved and destroyed. This resulted in the introduction of foreign ions into the copper-plating bath, and also heavily contaminated the bath. As a result, the bath could not be further used. No copper layer was formed, and the sheet sections had to be discarded. This process is particularly complicated and nonfunctional.
Copper-plating baths as in comparative example 1 and example 2 were used, but with greater variation in their chemical composition. Hull cell sheets made of ST2 steel as in comparative example 1 and example 2 were then cleaned and treated.
Table 1 illustrates the wide range in the chemical composition and the hath temperature of the copper-plating solution, as well as the treatment times in order to produce good copper layers. In the coating of iron materials, it was possible to vary the pH between 0.1 and 1 without adverse effects, while for zinc-rich materials, the pH could be varied between 6.5 and 7.0 without adverse effects. The bath temperature could be varied between 15° and 95° C. without adverse effects by adjusting the bath composition and/or treatment time. The duration of the electroless coating could be varied between 3 seconds and greater than 30 minutes without adverse effects by adjusting the bath composition and/or bath temperature. The adhesion of the applied layers was tested using cross-cut, wipe, and bending tests according to DIN EN ISO 2409, DIN EN ISO 1519, and ASTM 2794. All examples showed good adhesion.
These tests showed that at higher concentrations, in particular of copper and/or acid, tower temperatures and/or shorter coating times were sufficient. Conversely, the tests showed that at lower concentrations, in particular of copper, and/or for acid, for higher temperatures and/or longer coating times, temperatures of at least 15° C. and/or coating times of at least one minute are advantageous in forming pore-free and well-adhering copper layers. It was surprising that electroless copper plating could be carried out so successfully and flexibly. Thus, process advantages were shown, not just compared to copper layers of the prior art, in particular for hollow bodies.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 039 383.5 | Aug 2010 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/063752 | 8/10/2011 | WO | 00 | 2/15/2013 |
