EP1366219B1 - Bath for the galvanic deposition of gold alloys and the use thereof - Google Patents

Description

The invention relates primarily to a bath for the electrodeposition of gold and gold alloys and its use. In this bath, the gold is in the form of a gold sulfite complex.

It has been known for a very long time to electrodeposit gold or gold alloys from preferably aqueous solutions containing the gold or the corresponding alloying metals. After initially predominantly cyanidic gold baths were used, baths based on gold sulfite complexes have become increasingly important in recent times. This was mainly due to the fact that the gold sulfite baths are non-toxic compared to the cyanidic gold baths, in which hydrogen cyanide is known to be released. This non-toxicity and the good quality of the deposited layers has meant that the gold sulfite baths are being used more and more often despite their higher production costs and despite the problems with the stability of the baths, in particular in the field of dental technology. In addition, baths based on Goldsutfit complexes are comparatively easy to handle, which plays an important role for users without pronounced chemical-technical expertise such as dental technicians, dentists and their staff.

Particularly in the field of dental technology, special requirements are placed on electrodeposited precipitates. In addition, these requirements still vary depending on the type of dental framework or prosthetic molding produced. Thus, a homogeneous layer structure, ie a homogeneous microstructure, is as uniform as possible Layer thickness and a reproducible composition of the deposited layer prerequisite to be able to apply a ceramic or plastic veneer on the molding then. This is especially true for Keramikverblendungen where the molding must be fired after application of the ceramic composition at higher temperatures. In these cases, the metallic skeleton must also have the necessary stability to firing. With regard to other properties, such as wear resistance, porosity, corrosion resistance and others, minimum requirements must be met. In addition, the deposited layers must satisfy particular aesthetic requirements, especially in the field of dentistry, for example, in terms of color, gloss or surface texture. Finally, certain further requirements can be placed on the composition of the deposited layers, for example with regard to biocompatibility. Biocompatibility of the materials may be particularly important in the dental field, since, for example, allergy patients require gold or gold alloy layers with the highest possible purity.

Regardless of their field of application, and regardless of the form in which the gold is present in the bath, gold and gold alloy baths contain certain additives to at least partially meet the requirements imposed on the electroplating precipitations. Such additives are also referred to as fine grain additives or gloss additives. These may be organic additives, such as polyamines, polyimines and mixtures thereof or semi-metal compounds, for example arsenic, antimony or thallium. All of these additives can be incorporated more or less strongly in the deposited gold layer. In the case of organic additives, this is problematical in the dental field, since the layer properties (eg ductility and firing stability) can be negatively influenced by this incorporation. The incorporation of the semi-metals is in the dental field in particular arsenic and thallium problematic because then a required biocompatibility through the use of these toxic substances is no longer guaranteed. This leads to the fact that to the knowledge of the applicant currently only in the dental field antimony as an additive has gained importance. Physiologically, however, a replacement of the antimony compounds used is not undesirable. When blending prosthetic moldings with dental ceramics, however, no other metal compounds have proven suitable for reasons of firing stability except antimony compounds.

Another problem with the additives known to date for gold and gold alloy baths, in particular for baths based on gold sulfite complexes, is that these additives generally have to be added directly before the use of the corresponding baths. This is because the compounds contained in these additives are not stable in the respective baths, but decompose with the loss of their effectiveness over time. This may, for example, be due to the pH of the corresponding baths or because the additives react with other constituents contained in the bath.

In the case of the addition of antimony compounds to baths based on gold sulfite complexes, the antimony is usually used as Sb (III), for example as potassium antimony tartrate. The latter reacts in the bath to gelatinous antimony oxide hydrate gel, which probably constitutes the mode of action of this additive. The antimony oxide hydrate gel, in turn, is not stable under the usual bathing conditions and reacts to form crystalline antimony oxide which no longer exhibits the desired effect. This is the reason that the additive can be added to the bath only before use and that the additive loses its effect after some time. Thus production of a long-term functional gold or gold alloy bath with all necessary components is not possible.

In addition, it is problematic that the additives must not only be added later, but also that the correct dosage, d. H. the necessary amount of additive, depends on the other bath and process parameters. As influencing factors here are, for example, the proportions of the other constituents in the bath, the concentration of the electroactive ions, the geometry of the separation vessel (cell geometry), the temperature and the current density. In most cases, these problems are attempted to be solved by the user following a so-called dosage table of the manufacturer of the bath due to his lack of chemical-technical expertise and measuring the amount of additive according to the number of objects to be electroplated. Since the objects to be electroplated vary greatly in shape and size and the desired layer thickness of the precipitate and accordingly also the amount of metal to be deposited, such a dosage per object is subject to a comparatively large error. This can lead to very different qualities of the galvanic precipitation, so that even objects that are coated simultaneously in one operation can differ in the composition of the precipitate. This can make the deposition difficult to handle for the user.

In the EP-B1-0 126 921 describes an aqueous bath for the electrodeposition of gold-copper-bismuth alloys containing the gold in the form of a gold cyanide complex. This ternary alloys are deposited with high bismuth levels. The bath described there is particularly suitable for the deposition of pink to violet-colored coatings on decorative objects, such as jewelry, watches and glasses. The technical significance of this is that the bismuth can be incorporated into the alloys with extremely high contents up to 30 wt .-% and higher. This should be new applications, such. B. the processing of electronic Components, such as connectors, tap because the corresponding precipitates are particularly hard and have good electrical conductivity and abrasion resistance. For the dental field are in the EP-B1-0 126 921 mentioned baths, among other things, both due to their high toxicity and due to the fact that the bismuth is to be incorporated with high levels in the alloy, not suitable.

The DE-C2-2 723 910 (equivalent to FR-A-2353656 ) claims a variety of additive mixtures for baths for the electrodeposition of gold or gold alloys. These additional mixtures should cause an improvement in the properties of the deposited precipitates. Mandatory components of these additional mixtures are at least one organic water-soluble nitro compound having a specific general formula and at least one water-soluble metal compound of an element of the group arsenic, antimony, bismuth, thallium and selenium. Additional mixtures which contain a water-soluble bismuth compound in addition to the nitro compound are also limited to use in cyanidic baths. In baths based on a gold sulfite complex, the use of an additive of nitro acid and antimony-potassium double tartrate is proposed by this document. The use of in the DE-C2-2 723 910 mentioned additional mixtures and the gold baths produced therefrom is limited to the technical use for the cladding of electronic components for semiconductor technology.

Next is from the US-A-5,277,790 an additive for a bath based on a gold sulfite complex, which also necessarily contains both an organic polyamine or a mixture of polyamines and an aromatic organic nitro compound. The DE-A1-3 400 670 describes a gold sulfite complex-based bath that has an additive of water soluble thallium salt and a carboxylic acid free of hydroxyl and amino groups.

The object of the invention is to provide a bath for the electrodeposition of gold alloys, which at least partially avoids the disadvantages described above. In particular, the galvanic production of prosthetic dental moldings should be made even more reliable and safer and the handling of the baths used for this purpose should be further simplified. In addition, the possibility should be created to give the user an already provided with all necessary components and additives and thus functional bathroom in the hand. Finally, the corresponding baths should be able to be operated largely with biocompatible, ie physiologically harmless compounds, without the quality of the deposited layers is deteriorated.

This object is achieved by the bath with the features of claim 1 by the use with the features of claim 14, 21 and by the method of claim 15. Preferred embodiments of these objects of the invention are described in the dependent claims 2 to 13 and 16 to 22 is shown. The wording of all claims is hereby incorporated by reference into the content of this specification.

The bath according to the invention for the electrodeposition of gold alloys based on a gold sulfite complex is characterized in that it contains at least one bismuth compound in addition to any other metal compounds and other conventional additives / additives for such gold sulfite baths. This bismuth compound is preferably a water-soluble bismuth compound, which results in that the bath itself is preferably an aqueous bath.

In principle, all suitable inorganic or organic bismuth compounds are suitable as the bismuth compound. The bismuth compound is preferably a complex compound, preferably a so-called chelate compound. Such compounds are known cyclic compounds in which a ligand (complexing agent) occupies several coordination sites of a central atom (metal), so that these are usually particularly stable complex compounds. According to the invention it is further preferred if the bismuth compound contains an organic complexing agent, preferably an organic chelating agent. NTA (nitrilotriacetic acid), HEDTA (N- (2-hydroxy-ethyl) -ethylenediaminetriacetic acid), TEPA (tetraethylenepentamine), DTPA (diethylenetriaminepentaacetic acid), EDNTA (ethylenedinitrilotetraacetic acid) and as preferred complexing agent / chelating agent EDTA (US Pat. Ethylenediaminetetraacetic acid).

In addition, bismuth compounds employable in the present invention are, for example, water-soluble bismuth salts (e.g., sulfates, nitrates, sulfamates, phosphates, pyrophosphates, acetates, citrates, phosphonates, carbonates, oxides, hydroxides, and the like). In addition to the above-mentioned preferred complexing agents such as NTA and the like. Examples which may be mentioned of organic complexing agents include organic phosphonic acids, carboxylic acids, dicarboxylic acids, polyoxycarboxylic acids, hydroxycarboxylic acids, diketones, diphenols, salicylaldehydes, polyamines, polyaminocarboxylates, diols, polyols, di-polyamines, aminoalcohols, aminocarboxylic acids, aminophenols.

In the invention, it is further preferred if the bismuth compound (or possibly several such compounds) in the bath in a concentration between 0.05 mg / l and the saturation concentration of bismuth compound (s) in the bath is (are) included. In particular, concentrations in the bath between 0.05 mg / l and 1 g / l are preferred. Generally low Concentrations are preferred, within the last-mentioned range concentrations between 0.1 mg / l and 10 mg / l are to be emphasized.

In a particularly preferred embodiment, the bath according to the invention is substantially free of physiologically harmful (harmful) additives / additives, the bath preferably being free of arsenic, antimony and thallium compounds. In this way, it is achieved that no health-hazardous compounds, in particular metals, which could restrict the usability of the layers or of the resulting prosthetic shaped parts in dental technology, are incorporated into the deposited layers. Surprisingly, it has also been found that the addition of bismuth compounds according to the invention is also capable of reducing or even preventing the incorporation of physiologically questionable additives into the prosthetic molding. Thus, conventional gold sulfite baths, as already mentioned, contain at least one antimony compound as an additive. Accordingly, the antimony is incorporated into the prosthetic molding in a concentration of normally 0.2 per thousand. With the simultaneous addition of an antimony compound such as potassium antimony tartrate and a bismuth compound such as bismuth EDTA, however, it has surprisingly been found that both antimony and bismuth are present in the deposited molding in amounts of less than 30 ppm and 40 ppm (these are the Detection limits for the analytical method used for these elements). This shows on the one hand that the bismuth itself is not incorporated into the molded part and on the other hand that the bismuth is able to considerably reduce the incorporation of the antimony.

The concentration of gold in the bath according to the invention is generally not critical. Preferably, the gold is contained in the bath in a concentration between 5 and 150 g / l. In particular, gold concentrations in the bath selected between 10 and 100 g / l, preferably between 10 and 50 g / l. A particular advantage of the invention is that gold concentrations in the bath between 30 and 48 g / l can be selected. These comparatively high concentrations make the bath according to the invention particularly suitable for the rapid deposition of thick layers, as is fundamentally desirable in the field of the production of prosthetic molded parts in dental technology. Particularly in the case of baths with high gold concentrations, prosthetic moldings with layer thicknesses of about 200 μm can be obtained in less than 14 hours, preferably in less than 12 hours. It is even possible, with suitable process control, to deposit molded parts with such layer thicknesses in less than 6 hours. The particular advantages of the invention are also evident in deposits made in less than two hours, preferably within one to two hours. In this context reference is also made to the examples.

In the invention, at least one other metal is contained in the bath. This metal can be incorporated into the deposited layer and in these cases be referred to as alloying metal. In other cases, however, it can only serve to (better) deposit the gold or gold alloy layer. This metal may in particular be copper and / or iron and / or at least one noble metal. In the case of the addition of precious metals, preference is given to those from the so-called platinum group, in which case these are, in particular, palladium or platinum. Precious metals, in particular those of the platinum group, are particularly suitable because of their high biocompatibility in the field of prosthetic dental moldings.

The concentration of the further metal in the bath is, for example, also within the range of the desired alloy to be deposited wide borders variable. In principle, the metals may be added in the form of their preferably water-soluble compounds, in particular salts or in the form of preferably water-soluble complex compounds. In this connection, the complex and chelating agents already mentioned above for bismuth can also be used in particular. Preferably, the concentrations of the metal compounds can be selected between 0.1 mg / l and 200 g / l. Within this range, the concentration may be between 0.1 and 500 mg / l, more preferably between 1 and 20 mg / l. Again, low concentrations are preferred. Within the latter range, concentrations between 2 mg / l and 10 mg / l are more preferred.

The gold sulfite complex in the bath according to the invention may in principle be any known complexes known from the prior art. Preferably, it is a so-called ammonium-gold sulfite complex, in which therefore the gold ion is complexed by the sulfite ions and as a "counterion" at least one ammonium ion is present.

The baths of the invention preferably have a pH of at least 7, i. they are either neutral or alkaline. In particular, the baths are (weakly) alkaline, with pH values of 7 to 9 being preferred.

The preferred ammonium-gold sulfite complex has a number of advantages over other gold sulfite complexes. For example, compared to sodium / potassium-gold sulfite complexes, a markedly increased stability of the complex in the gold bath is responsible for a number of advantageous properties. These are, for example, a longer shelf life, a lower sensitivity to contamination and a lower photosensitivity. In addition, baths with ammonium-gold sulfite complexes be operated at significantly lower pH of about 7-9. This makes handling such baths easier and safer for users with a lack of chemical expertise over Na / Ka-gold sulfite complex baths with pH's of about 10.

Surprisingly, in the bath according to the invention, which is based on the preferred ammonium-gold sulfite complex and contains at least one bismuth compound, a particularly advantageous relationship between the chemical composition of the gold bath and the chemical composition of the galvanic precipitate has resulted. This is further improved by the presence of the further metals in the gold bath, in particular copper and / or at least one noble metal and / or iron. In addition, an extended range of applications has been identified, as apart from gypsum, a whole range of dental modeling and framework materials can also be used in the gold bath.

Thus, by using the bismuth compound in an astonishingly simple manner, it has been possible to precisely control and predictably adjust the composition of the galvanized gold layer and its functional properties. So far, this has not been possible, or only to a limited extent, with the known gold baths used in dental technology, so that the composition of the deposition there is usually limited by technical factors, such as e.g. Electrode geometry and the other device-related factors is determined.

As already mentioned several times, the requirements for a gold bath and the electrodeposited layers in the field of dental technology are of a special nature, so that here, in addition to the requirements mentioned above, again referred to the biocompatibility and the desired gold or gold alloy layers with the highest possible purity shall be. That's why it's special Importance to control the composition of the galvanic precipitation targeted and reproducible set.

In the case of the preferred further metal copper, moreover, it has been shown that in these preferred baths according to the invention a certain amount ratio between bismuth and copper is advantageous for the composition of the gold layer. It was surprising in this case that the customary influencing parameters known to the person skilled in the art of galvanic deposition, such as, for example, Electrode geometry, plating time, current density, temperature, current shape, etc. have only a minor effect on the deposition. Thus, by adjusting the bismuth-copper ratio in the bath, the copper content in the gold layer can be determined accurately and reproducibly. The advantageous for dental technology high purity can thus be achieved deliberately by targeted control of a low copper content of the layers without the functionality of the layers suffers. By selectively incorporating low levels of copper into the gold layer while avoiding the incorporation of bismuth, in addition to the high purity, the functional properties of the gold layer can also be precisely controlled, e.g. Hardness, gloss, surface properties, color etc.

If in the presence of copper and bismuth in the bath as pure as possible gold layers are deposited, the ratio of bismuth: copper (based on the metals) is <1, in particular between 0.3 and 0.5. If copper alloys are used to deposit alloys, this ratio is> 1.

In the case of iron as further metal in the gold bath, surprisingly, further advantages of the bath according to the invention have emerged. Iron is safe to handle and is needed as an essential trace element even by the body. It also allows on the one hand by selecting the bismuth to iron ratio in the gold bath and, on the other hand, by choosing the type of iron compound / iron complex compound, to control even more precisely the composition and properties of the deposited gold layer.

For example, in the iron complexes Fe-DTPA, Fe-EDTA, Fe-EDNTA with bismuth-iron ratios of about 1.5 to about 2 were particularly advantageous gold layers. In contrast, when iron citrate is used, an advantageous bismuth: iron ratio is about 0.18 to about 0.3.

Of particular importance in this case was the surprising finding that, despite the advantageous effect of the iron compounds during deposition, no iron (<10 ppm) is incorporated into the gold layer. This makes it even possible, for example, gold layers with a purity of up to 99.99% and excellent technical properties, such as. to galvanize absolutely reproducible firing stability. This has not been the case with conventional gold electrolytes capable of depositing such pure layers.

Furthermore, it was surprising that, despite the different position of copper and iron in the electrochemical series, both metals can also be used together in a variety of proportions to bismuth in the bath according to the invention. This opens up a broad spectrum of new control possibilities for the properties, the composition and the function of gold and gold alloy layers of baths according to the invention due to the large number of possible combinations for the bismuth-copper-iron ratios. In cases where bismuth, copper and iron are present in the bath at the same time, the proportions of bismuth: copper are preferably> 0.4 and of bismuth: iron> 0.3. Surprisingly, it has also been shown that in the bath according to the invention (with the bismuth compound and the interaction of the above-described additions of compounds of other metals in gold bath still preserves the initially described reduction or prevention of the incorporation of physiologically harmful additives / additives in the electroplated layer The bath according to the invention can thus selectively prevent the incorporation of, for example, antimony, even in the presence of various metals such as, for example, copper and / or iron.

As already mentioned, the bath according to the invention may contain other conventional additives / additives which are usually contained in such baths based on a gold sulfite complex. Such additives / additives are known to the person skilled in the art and can be varied within the scope of their specialist knowledge in the customary fields. For example, conductive electrolytes with their conductive salts, buffer systems / buffer mixtures, so-called stabilizers and wetting agents are present. Possibly. it is also possible to include brighteners and / or fine grain additives known from the prior art in the bath according to the invention.

The invention further includes the use of the described inventive bath for the production of prosthetic moldings for the dental sector by means of electrodeposition. Such a use is in particular for the production of so-called dental frameworks such as crowns, bridges, superstructures and the like. intended. The prosthetic moldings are thereby electrodeposited on a substrate. One speaks here also of the so-called Galvanoforming. The self-supporting stable molded part is separated from the substrate and further processed. The substrate can be, for example, a model molded from a tooth stump or an implant abutment part (prefabricated or individually preprocessed).

In a corresponding manner, the invention comprises the use of at least one bismuth compound, preferably at least one water-soluble bismuth compound for producing prosthetic moldings for the dental sector by means of electrodeposition. In particular, the bismuth compound is used as part of a bath according to the invention, as described above. Preferred bismuth compounds have already been explained in detail above, so that reference can be made to the corresponding parts of the description and reference can be made.

It should be emphasized as a particularly important feature of the invention that the bismuth compound used according to the invention and optionally also the compounds of further metals can be added to the bath directly during its preparation. This means that the user is provided with a bathroom that is functional with regard to all components and additives. In contrast to the known baths of the prior art, the user does not have to add any additive / additive before carrying out the electroplating process, which would be associated with the disadvantages already explained above.

It should be noted, however, that a dosing of the bismuth compound used according to the invention to the bath can also take place before or during the electrodeposition, if so desired. Such a variant can also be provided, for example, if an aqueous bath is used to which a completely or partially water-insoluble bismuth compound, eg bismuth oxide, has been added during the preparation. This water-insoluble compound can then be converted into a water-soluble bismuth compound by adding a suitable complexing agent immediately before or during the electrodeposition, which then unfolds the desired effect in the bath.

As a further preferred variant of the invention is the case to be mentioned that the bismuth compound is added after a galvanic deposition to supplement in the bath. This concerns the cases where the concentration of gold and / or further metal in the bath is sufficient for several, in particular a plurality of deposits. Then the bismuth compound (and possibly also the compounds of the other metals) can be supplemented accordingly for later deposition cycles.

As already briefly mentioned, the use according to the invention is intended for the production of prosthetic molded parts which have sufficient stability in the electroforming process. Accordingly, layer thicknesses of the molded part of more than 10 μm are usually provided. The layer thicknesses of the molded part are preferably between 100 and 300 μm, with layer thicknesses of approximately 200 μm in particular being deposited. By providing such layer thicknesses, the invention is suitable not only for the production of crowns, but also of bridges and other superstructures.

Finally, the invention comprises a method for the production of prosthetic moldings for the dental sector from gold alloys by electrodeposition. In particular, this method is for the production of dental structures such as crowns, bridges, Suprakonstruktionen and the like. intended. In this method, according to the invention, a gold or gold alloy layer is deposited from a bath according to the invention on a corresponding substrate and the resulting layer is separated from the substrate (demolded). As mentioned above, the substrate may be e.g. a model molded from a tooth stump or an industrially prefabricated or individually machined implant abutment.

Preferably, the substrate is constructed of an electrically non-conductive material, in particular gypsum or plastic. This usually applies the cases in which a model was molded from the tooth stump. The surface of the non-conductive substrate is then made conductive prior to electrodeposition, in particular using conductive silver.

In other preferred cases, the substrate is made up of at least one metal which itself is already conductive. Here are as substrates, for example, inner telescopes (usually from a cast and milled dental alloy) or implant abutment parts, such as implant abutment posts and the like. to call. Such parts are often made of titanium or titanium alloys.

The process according to the invention and also the uses according to the invention are preferably characterized in that the deposition takes place at high current densities, which usually results in low electroplating times. Preferably, current densities up to 10 A / dm ² , in particular current densities up to 8 A / dm ^{2 are} selected. Even with such high current densities, the bath according to the invention is still very easy to use.

The use according to the invention or the method according to the invention can preferably be carried out in such a way that the deposition takes place in the so-called pulse-plating method. This type of electrodeposition also uses direct current. However, this direct current is applied as pulse current, ie in the form of current pulses interrupted by pauses. For example, the state of the art can be referred to the volume " Pulse-Plating "the series Galvanotechnology and surface treatment, Leuze-Verlag, Saulgau, 1990 to get expelled. The application of the pulse-plating method in dental technology shows the DE-A1-198 45 506 the applicant, the content of which is incorporated herein by reference. The application of the pulse-plating method In the present invention has the advantage that within relatively short times, the precipitates in the desired thickness, for example of about 200 microns, can be deposited.

The use according to the invention and the method according to the invention are furthermore preferably characterized in that the deposited prosthetic shaped part is veneered with ceramic and / or plastic during its further processing. In this way, the desired dentures is made. A ceramic-veneered molding is fired in a conventional manner after application of the ceramic, for example at temperatures up to about 950 ° C. A molded part which is veneered with plastic is irradiated with light, in particular with visible light, after the plastic has been applied to cure it, after the surface of the molded part has been previously conditioned with suitable methods known to the person skilled in the art.

As already mentioned in part, and as the examples listed below show, a number of advantages are associated with the invention.

Thus, the bath according to the invention is outstandingly suitable for the production of prosthetic moldings (dental prosthetic parts). The properties of the precipitation are at least as good as those deposited during precipitation from gold sulfite baths, which work, for example, with an addition of antimony compounds. The quality of the precipitation corresponds to the bath according to the invention even better the specific requirements in dental technology.

The obtained with the bath according to the invention pure gold layers are golden yellow and high gloss, so that they are particularly high aesthetic Meet requirements. Of course, optionally also matte and / or rough surfaces can be produced. The firing stability of these layers, which is unavoidable for their ceramic veneering, is given with reproducible security despite the possible omission of an antimony compound in the gold bath. So far, to the knowledge of the applicant, this is not the case with any bath which can work without an antimony compound.

Another advantage of the bath according to the invention is that it is obviously insensitive to introduced into the bathroom plastics, for example, as Zahnstumpfmaterialien or for covering metallic parts that are not to be electroplated, are provided. In the prior art baths, such plastics (molded model plastics) or lacquers (topcoats) release components during deposition in the gold bath which have a negative effect on the effect of the fine grain or brightener additives of the gold bath. This negative effect is usually the more pronounced, the higher the current density is chosen during the deposition. This results in the invention in the advantage that due to the insensitivity of the bath against such interference at relatively high current densities (see above up to 8 A / dm ² or 10 A / dm ² ) can be used.

It must also be mentioned that the workability of the bath according to the invention with the same requirement profile of the deposited galvano layers is absolutely comparable to conventional baths based on gold sulfite complexes which work, for example, with antimony or arsenic additives. It is even possible to increase the workability with appropriate choice of Bismutzusatzes over known baths still.

The possibility of using the bismuth additives in the bath according to the invention on compounds which are possibly harmful to health, e.g. of arsenic, thallium and, where appropriate, of antimony, has already been mentioned above.

A further advantage of the bath according to the invention is surprisingly found in the fact that such a bath with bismuth additive works problem-free and with above-average results in various devices commercially used in the dental field (also of different manufacturers) for electrodeposition. Normally, either the gold or gold alloy bath in its composition had to be precisely matched to the device used, or such a device in particular in its process parameters exactly to a particular bathroom. This has resulted in each manufacturer usually offering a specific gold bath for a specific device, tuned to its process parameters for this gold bath.

With the bath according to the invention, it is now possible, for example, to operate various devices with this gold bath without these devices having to be set in a complicated manner to this bath. Thus, for example, an Applicant's AGC microdevice which achieves a layer thickness of 200 μm, usually in 12 hours, can be operated just as well with the bath according to the invention as an AGC MicroPlus device which already achieves the same layer thickness in 5 hours. The bath according to the invention is also suitable for use in devices which use the pulse-plating process, for example the Applicant's AGC Speed device. In such devices, layer thicknesses of 200 microns depending on the size of the part to be plated in 1 to 2 hours can be achieved. Thus, the bath according to the invention can be advantageously adapted to existing galvanic devices of the user. The application range from "slow" up to the "fastest" devices, which can also be operated fully automatically, illustrates the particularly good handling of the invention for the user.

Finally, it should be mentioned again that the addition of a bismuth compound present in the baths according to the invention can already be added during the preparation of the bath. This results in the user being provided with a completely functional bath without it being absolutely necessary to add further additives before electroplating. In addition, it has been found that the baths according to the invention with the Bismutzusatz are stable over long periods. This means that the bath is functional even after a longer storage time and the additive does not lose its effectiveness. All this leads both to the manufacturer of the bath and to the user to better handling and process reliability in carrying out the electroplating process, since all sources of error that can occur in the subsequent addition of additives are excluded from the outset.

The described features and further features of the invention will become apparent from the following description of preferred embodiments in conjunction with the subclaims. In this case, the individual features can be implemented individually or in combination with each other.

Examples (not according to the invention)

For the galvanic deposition of prosthetic moldings made of gold or gold alloys carried out according to the present examples, it is possible to use customary electrolysis cells, as known from the prior art and also commercially available. Depending on the desired process control, it may, for example the Applicant's ^AGC® devices labeled "Micro", "Micro 5h", "Micro Plus" or "Speed".

An electrolysis cell which can be used according to the examples consists of a vessel for receiving the bath. This vessel is usually provided with a cover. Further, an anode, which may possibly consist of several parts, as well as at least one cathode is provided. On this cathode, which is formed, for example, of the substrate such as a plaster stump or mounting post, the gold or gold alloy is electrodeposited. The anode consists for example of platinized titanium. For the deposition itself, a suitable current / voltage source is provided. Furthermore, a magnetic stirrer with heating is usually provided, which at the same time ensures a constant (normally elevated) deposition temperature in the bath and for driving a magnetic stirrer bar present in the electrolysis cell. Accordingly, a temperature sensor is introduced into the electrolytic cell.

It is expressly pointed out that, according to the invention, no special configuration of the electrolysis cell or of the apparatus containing this electrolysis cell is necessary. The skilled worker is readily aware of the corresponding equipment for deposition from gold sulfite baths.

• Gipsstümpfe/Gipsmodelle, die mit Leitsilber leitfähig gemacht wurden,
• gegossene und gefräste Innenteleskope, bei denen nicht zu galvanisierende Teile mit einem entsprechenden Kunststoff aufgefüllt sind und die zu galvanisierende Fläche mit Leitsilberlack bestrichen ist,
• Aufbaupfosten zur Herstellung käppchenartiger Formteile, die auf Implantataufbaupfosten zementierbar sind, und
• Gipsmodelle, die eine Verblockung zur Verbindung von zwei nebeneinanderliegenden Zähnen aufweisen, und die ebenfalls mit Leitsilber beschichtet sind,
  galvanisch beschichtet.

As already explained in the description, according to the examples (only as a selection)

• Plaster stumps / gypsum models rendered conductive with conductive silver,
• cast and milled inner telescopes in which parts that are not to be electroplated are filled with a suitable plastic and the surface to be electroplated is coated with conductive silver lacquer,
• Mounting posts for producing coping-like moldings which are cementable on implant mounting posts, and
• Plaster models having a block for connecting two adjacent teeth and also coated with conductive silver,
  galvanically coated.

Bath composition, deposition parameters, substrate and deposition result of the examples carried out are shown in Table 1. In all cases, the particularly advantageous bath based on an ammonium-gold sulfite complex was used.

The baths used in addition to the specified ingredients usual additives / additives for gold sulfite baths. These additives are known to the person skilled in the art. These are, for example, conductive salts (sulfites, sulfates and phosphates), wetting agents or stabilizers such as nitro acids. The bath according to the invention differs from the known baths in particular by the addition of bismuth compound, due to this addition, additives (if any) present in conventional baths, such as antimony compounds or nitro compounds, may (but need not) be omitted.

If the separation result of the following table refers to a "defect-free" functionality, this is to mean that the layer obtained during the deposition has no cracks, pores or holes.

Claims (22)

1. A bath for the galvanic deposition of gold alloys, in which bath the gold is present In the form of a gold sulfide complex, the bath comprising at least one water soluble bismuth compound, at least one copper compound or an iron compound and at least one further metal compound as well as usual additives for gold sulfide baths of this kind, characterized in that the further metal compound comprises platinum as precious metal.
2. The bath as claimed in claim 1, characterized In that the gold sulfide complex is an ammonium gold sulfide complex.
3. The bath as claimed in claim 1 or claim 2, characterized in that it has a pH value of >7, preferably 7 to 9.
4. The bath as claimed in one of the preceding claims, characterized in that the bismuth compounds and the compounds of the further metals are complex compounds.
5. The bath as claimed in claim 4, characterized in that the complex compounds contain organic chelating agents.
6. The bath as claimed in claim 5, characterized in that the chelating agents are NTA, HEDTA, TEPA, DTPA, EDNTA or in particular EDTA.
7. The bath as claimed in one of the preceding claims, characterized in that the bismuth compounds in the bath are present in a concentration of between 0,05 mg/l and the saturation concentration thereof in the bath.
8. The bath as claimed in claim 7, characterized in that the bismuth compounds in. the bath are present in a concentration of between 0,05 mg/l and 1 g/l, In particular between 0,1 mg/l and 10 mg/l.
9. The bath as claimed in one of the preceding claims, characterized in that the compounds of the further metals in the bath are contained in a concentration of between 0,1 mg/l and 200 g/l, preferably between 0,1 mg/l and 500 mg/l.
10. The bath as claimed in claim 9, characterized In that the compounds of the further metals in the bath are contained in a concentration of between 1 mg/l and 20 mg/l, preferably between 2 mg/l and 10 mg/l.
11. The bath as claimed in one of the preceding claims, characterized in that it is substantially free of physiologically risky additives, preferably free of arsenic, antimony and thallium compounds.
12. The bath as claimed in one of the preceding claims, characterized in that the gold in the bath is contained in a concentration of between 5 and 150 g/l.
13. The bath as claimed in claim 12, characterized in that the gold in the bath is contained in a concentration of between 10 and 100 g/l, preferably between 10 and 50 g/l, In particular between 30 and 48 g/l.
14. The use of a bath as claimed in one of preceding claims for the production of prosthetic moulded parts for the dental field by means of galvanic deposition, in particular for the production of dental frames such as crowns, bridges, superstructures and the like.
15. A process for the production of prosthetic moulded parts for the dental field from gold alloys by galvanic deposition, in particular for the production of dental frames such as crowns, bridges, superstructures and the like, characterized in that a gold or gold alloy layer from a bath according to one of the claims 1 to 3 is deposited on a respective substrate, for example on a model taken from the stump of a tooth, and which is then separated from the substrate.
16. The process according to claim 15, characterized in that the substrate is composed of an electrically nonconductive material, in particular plaster or plastics, the surface of which is rendered conductive in particular by means of conductive silver.
17. The process according to claim 15, characterized in that the substrate is composed of at least one metal.
18. The process according to one of the claims 15 to 17, characterized in that the deposition is effected at high current densities, preferably at current densities up to 10 A/dm².
19. The process according to one of the claims 15 to 18, characterized in that the deposition Is effected in a so-called pulse plating process.
20. The process according to one of the claims 14 to 19, characterized in that the prosthetic moulded part is veneered with ceramics and/or plastics.
21. The process according to claim 20, characterized in that a moulded part that has been veneered with ceramics, is fired.
22. The process according to claim 20, characterized in that a moulded part that has been veneered with plastics, is cured with light, in particular visible light.