EP0916747B1 - Electrolytic bath for the deposition of palladium and palladium alloys - Google Patents

Description

DE-195 28 800 A1 describes an alkaline or neutral bath for electroplating Deposition of palladium or alloys of palladium known, which 2 to 25 g / l palladium as diammino-dichloro-palladium complex, at least a conductive salt (in particular 5 to 300 g / l ammonium chloride and / or 5 to 300 g / l ammonium sulfate), a gloss agent (in particular 0.1 to 30 g / l nicotinic acid or nicotinamide), a wetting agent (in particular 0.1 to 5 g / l of an organic Phosphate esters or sulfate esters) preferably also a buffer substance such as boric acid and water.

The palladium or palladium alloy layers that can be deposited with it, are shiny and relatively ductile up to layer thicknesses of a few microns. However, if layers are deposited whose thickness exceeds 5 to 10 µm, then their ductility and luster decrease significantly. The lack of shine and one with the layer thickness increasing tendency to cracking make the deposited layers unsuitable for decorative purposes. The tendency to Crack formation can also be found in US 4,076,599 A, which is an alkaline Palladium bath (pH of 8.5 to 9.6), which also the palladium as a diammino-dichloro complex, in addition ammonium chloride as the conducting salt, ammonium sulfamate as a wetting agent and contains 1 to 1000 ppm of a sulfite. The bathroom is not used for decorative purposes, but for finishing electrical ones Contacts in low-voltage technology. Shine is not an issue here The thin layers of 2 - 3 µm required there showed up the palladium layers still crack free. With thicker layers, however, this is no longer the case Case.

DE-17 96 110 B2 describes a strongly alkaline bath for electrolytic deposition shiny palladium coatings known, which the palladium in Contains form of a urea complex dissolved by ammonia to a pH is set higher than 8 and a sulfite compound in a concentration contains from 1.5 to 70 g / l dissolved. Through the simultaneous use of ammonia and a sulfite compound are said to produce particularly white palladium coatings are, especially with relatively high sulfite contents.

However, it is also disadvantageous in this bath that the palladium coatings become brittle are and tend to crack and that the bath is not sufficiently stable; ammonia evaporates in substantial quantities from the bath, so that the pH sinks and the bathroom cannot be operated openly.

GB 2 094 836 A describes an alkaline bath for electrolytic deposition of palladium or palladium-nickel alloys known, which 5 to 30 g / l Palladium as chloride or sulfate complex, a conductive salt, one or more brighteners as well as contains water.

U.S. 5,415,685 discloses phosphonic acids and amine compounds such as e.g. EDTA or NTA as complex-forming additives for a bath Palladium deposition.

US 4,673,472 discloses a bath for the deposition of ductile, crack-free palladium layers, which nicotinic acid or nicotinic acid amide as a brightener contains.

From J.K. Dennis and T.E. Find: "Nickel and Chromium Plating", 1972 Newnes-Butterworths, London is adding a wetting agent to a metal depositing agent Bad known.

US 3,933,602 discloses sodium lauryl sulfate as a suitable wetting agent for baths for palladium deposition.

The present invention has for its object to provide the composition of a bath, from which palladium layers and palladium alloy layers can be deposited, which are characterized by high ductility and a low tendency to crack even when the layers are 10 microns thick or even thicker and are still reasonably shiny.

This object is achieved by an electrolytic bath with the in claim 1 specified features. Advantageous developments of the invention are the subject of subclaims.

The bath according to the invention contains 1 to 50 g of palladium in 1 l of bath liquid Chloride complex compound, as a sulfate complex compound, as a nitrate complex compound and / or as a nitrite complex compound, one or more conductive salts, one or more brighteners, one of which is N- (3-sulfopropyl) pyridinium betaine is one or more wetting agents and 0.01 to 3 g of a sulfite, where the quantity is based on the sulfite group. The bath is a watery one Bath and is at a pH between 6.0 and 9.5, preferably at one pH adjusted between 6 and 8.

• Erstaunlicherweise können Palladiumschichten und Palladium-Legierungsschichten abgeschieden werden, die sich selbst dann durch eine sehr hohe Duktilität auszeichnen, wenn die Schichten mehrere 100 µm bis zu einigen mm dick sind. Dadurch eignet sich das Bad für alle technischen Anwendungen, bei denen es auf duktile Palladiumschichten und Palladiumlegierungsschichten ankommt.
• Besonders eignet sich das Bad zur Erzeugung von Galvanoplastiken. Galvanoplastiken sind Formkörper, insbesondere Hohlkörper, die durch elektrolytische Metallabscheidung gebildet werden und insbesondere zur Schmuckherstellung und zur Herstellung von Brücken und Kronen in der Dentaltechnik verwendet werden. Das Verfahren zum Herstellen von Galvanoplastiken wird auch als Galvanoforming, Elektroforming oder Elektroformung bezeichnet. Ein Beispiel findet sich in der DE-39 18 920 C2.
• Die mit dem erfindungsgemäßen Bad erzeugten Schichten sind auch bei sehr hohen Schichtdicken seidenglänzend und können durch einen leichten Poliervorgang auf Hochglanz gebracht werden.
• Das Bad kann bei niedrigen Temperaturen, vorzugsweise bei 40° C, betrieben werden. Deshalb können niedrig schmelzende Wachsmodelle nach vorheriger Metallisierung, welche beispielsweise mittels eines Leitlackes erfolgen kann, direkt beschichtet werden. Wegen der niedrigen Arbeitstemperatur ist die Gefahr eines Abdampfens von Badbestandteilen, insbesondere von Ammoniak zur Einstellung des pH-Wertes, gering, was für die Belastung der Luft in der Umgebung des Bades und für die Stabilität des Bades günstig ist.
• Dadurch, daß das Bad mit einem pH-Wert zwischen 6 und 8 annähernd neutral betrieben werden kann, ist es in der Anwendung angenehm und der pH-Wert leicht stabil zu halten. Technisch wäre es allerdings auch möglich, den pH-Wert bis auf 9,5 zu steigern, doch wird das nicht bevorzugt.
• Das Bad kann mit Stromdichten in der Größenordnung von 1A/dm² betrieben werden und erlaubt wirtschaftliche Abscheideraten.

The bathroom has convincing advantages:

• Surprisingly, palladium layers and palladium alloy layers can be deposited, which are characterized by a very high ductility even if the layers are several 100 µm to a few mm thick. This makes the bath suitable for all technical applications where ductile palladium layers and palladium alloy layers are important.
• The bath is particularly suitable for the production of galvanoplastics. Galvanoplastics are molded articles, in particular hollow articles, which are formed by electrolytic metal deposition and are used in particular for the manufacture of jewelry and for the manufacture of bridges and crowns in dental technology. The process for producing galvanoplastics is also referred to as galvanoforming, electroforming or electroforming. An example can be found in DE-39 18 920 C2.
• The layers produced with the bath according to the invention are silk-glossy even with very high layer thicknesses and can be brought to a high gloss by a light polishing process.
• The bath can be operated at low temperatures, preferably at 40 ° C. Therefore, low-melting wax models can be coated directly after prior metallization, which can be done, for example, with a conductive varnish. Because of the low working temperature, the risk of evaporation of bath components, in particular ammonia to adjust the pH, is low, which is favorable for the pollution of the air in the vicinity of the bath and for the stability of the bath.
• The fact that the bath can be operated almost neutral with a pH value between 6 and 8 makes it pleasant to use and the pH value can be kept slightly stable. Technically, however, it would also be possible to raise the pH to 9.5, but this is not preferred.
• The bath can be operated with current densities in the order of 1A / dm ² and allows economical deposition rates.

The palladium content is not critical. The bath should not be less than 1 g Contain palladium per liter, otherwise the deposition rate will be too low. At the The bath is most economical with palladium contents between 5 and 15 g / l operate.

An example of a palladium chloride complex compound is [Pd (NH ₃ ) ₄ ] Cl ₂ . Such a bath can contain nickel chloride to form an alloy component and ammonium chloride as the conductive salt. An example of a palladium sulfate complex compound is [Pd (NH ₃ ) ₄ ] (SO ₄ ). A bath of this type may contain nickel sulfate to form a palladium-nickel alloy and ammonium sulfate as the conductive salt.

An example of a palladium nitrate complex compound is [Pd (NH ₃ ) ₄ ] (NO ₃ ) ₂ . A bath of this type can contain sodium nitrite and sodium sulfate as conductive salts and can be adjusted to a pH between 6 and 8 with potassium hydrogen phosphate and ammonia.

An example of a palladium nitrite complex compound is [Pd (NH ₃ ) ₄ ] (NO ₂ ) ₂ . A bath of this type can contain, for example, sodium nitrite and ammonium nitrate as conductive salts.

The addition of palladium as the diammino-dichloro complex [Pd (NH ₃ ) ₂ ] Cl ₂ , which dissolves in an ammoniacal bath to form the tetrammino-dichloro complex [Pd (NH ₃ ) ₄ ] Cl ₂ , from which the palladium is obtained, is particularly suitable can be deposited.

Above all, nickel, cobalt, zinc and copper are used as alloy components an amount not exceeding 50% by weight of the palladium. By the alloy metal can shine and ductility of the deposited Influence layer favorably; this applies in particular to zinc. The optimal zinc content the bath is between 0.3 and 0.6 g / l. The zinc can e.g. as zinc sulfate be added. To bind the zinc complex, one can be used for this purpose Conventional complexing agents are added, for example a phosphonic acid or a complexing amine compound such as e.g. EDTA or NTA. A special one is a suitable complexing agent for the zinc 1-hydroxy-ethane-1,1-diphosphonic acid, which is preferably in amounts of 5 g / l up to 50 g / l is contained in the bath.

The required conductive salt can be selected from the group commonly used in electroplating Conductive salts can be selected. Ammonium, sodium and and potassium salts of sulfuric acid and hydrochloric acid, especially ammonium chloride and ammonium sulfate, which contain in amounts of 5 to 300 g / l in the bath could be.

To increase the level of gloss, the bath can use nicotinic acid, nicotinic acid amide or similar compounds known for this purpose can be added. However, an addition of is particularly suitable as a brightener N- (3-sulfopropyl) pyridinium betaine in an amount of 0.002 to 5 g / l, preferably from 0.002 to 0.05 g / l, best 0.01 g / l; this addition is from DE 44 28 966 A1 (page 4, line 55) known per se, but judged there as unsuitable because it has caused cloudy palladium deposits. It is all the more surprising that a Add N- (3-sulfopropyl) pyridinium betaine in a bath with the inventive Composition leads to bright, silky glossy palladium layers. It is also surprising that when using an addition of N- (3-sulfopropyl) pyridinium betaine deposited much thicker palladium layers than when using other brighteners such as nicotinic acid or nicotinamide. The thicker the deposited palladium layers the more you tend to crack, which, as at the beginning already mentioned, can be used for layer thicknesses over 2-3µm. Using an addition of N- (3-sulfopropyl) -pyridinium betaine, however, can be silk-gloss Layers of palladium and alloys of palladium crack-free generate which are several hundred micrometers up to a few millimeters thick are. So N- (3-sulfopropyl) pyridinium betaine has a surprisingly cheap one Influence on the ductility and freedom from cracks in the deposits and opens the Palladium bath the important field of electroplating or electroforming.

Complex organic are suitable as additives that promote wetting Phosphate or sulfate esters, especially polyoxyethylene fatty alcohol ether or Sodium lauryl sulfate, which the bath expediently in an amount of 0.02 to 2 g / l, preferably 0.1 g / l can be added.

The sulfite provided according to the invention can be, for example, sodium sulfite. To achieve its beneficial effect on ductility, it should be contained at least in an amount of 0.01 g / l. However, the sulfite content (based on the SO ₃ group) should not be more than 3 g. If the amount of sulfite is increased significantly above 3 g / l, crystalline precipitates in the electrolyte become visible, which make the bath unusable. Although the crystalline precipitates can dissolve as the amount of sulfite is increased further, the then deposited palladium layers and palladium alloy layers are then brittle and show a very strong tendency to crack, which makes them unsuitable for the purposes of electroplating. Baths which contain less than 1.5 g / l sulfite are therefore particularly preferred.

The bath is preferably operated neutral or slightly alkaline. Tries, strongly acidic palladium baths by adding a sulfite have failed, because the sulfite then has a reducing effect and makes the bath unstable. At the the bath is best adjusted to a pH between 7 and 8, preferably by adding ammonia, the stability of the pH value by a Buffer substance, especially by boric acid, can be influenced favorably can.

Such a bath works satisfactorily at temperatures between room temperature and 70 ° C; it is preferably operated between 30 ° C and 50 ° C, with current densities between 0.2 and 3 A / dm ² .

A good bath composition is the following:

1st example

Add palladium as diamminodichloro complex 10 g / l

Conductive salt ammonium sulfate 40 g / l

Conductive salt ammonium chloride 40 g / l

Boric acid as pH buffer 20 g / l

Sodium lauryl sulfate as a wetting agent 0.1 g / l

N- (3-sulfopropyl) pyridinium betaine as brightener 0.01 g / l

Sulfite (as sodium sulfite) 1 g / l

Ammonia to adjust a pH of 7.6

Rest of water.

Metallized wax molds were coated with 320 μm palladium in 30 hours at a temperature of 40 ° C. and a current density of 0.8 A / dm ² . After removing the wax core, a silky, highly ductile palladium hollow form resulted.

2nd example

The first example was modified in such a way that the current density was increased to 1 A / cm ² . The coating yield was 32.3 mg / amine. The deposited palladium layers were light and silky shiny. When a 10 µm thick palladium layer was bent around a dome of 20 mm diameter by 90 °, no cracks occurred.

3rd example

The second example was modified so that the sulfite content was 3 g / l scam. The yield was 32.6 mg / amine. The palladium layers that it creates were bright and silky. A 10 µm thick palladium layer could be bent without cracks as in the second example.

Comparative example

The second example was modified so that the sulfite content to 4 g / l was increased. There were crystalline precipitates that made the bathroom unusable made.

Claims (14)

1. Electrolytic bath for the deposition of palladium and palladium alloys, containing in 1 litre of the bath solution:

   1 to 50 g of palladium in the form of a chloride, sulphate, nitrate and/or nitrous complex compound,

   one or more conducting salts,

   one or more glossing agents, one of them being N-(3-sulphopropyl)-pyridinium betaine,

   one or more wetting agents,

   0.03 to 3 g sulphite (SO₃ ^-)

   and water

   and being standardised to a pH value of between 6 and 9.6.
2. The bath as defined in Claim 1, characterised in that it contains 5 to 15 g/litre of palladium.
3. The bath as defined in Claim 1 or Claim 2, characterised in that it contains the palladium in the form of a tetrammino-dichlorocomplex.
4. The bath as defined in any of the preceding Claims, characterised in that it contains, as alloy component for the palladium, nickel, cobalt, zinc or copper in quantities not exceeding 50 percent by weight of the palladium.
5. The bath as defined in Claim 4, characterised in that it contains a phosphonic acid or an amine compound, such as ethylene diamine tetracidic acid (EDTA) or nitrilotriacidic acid (NTA) as a complexing agent for the alloy metal or metals of the palladium.
6. The bath as defined in any of the preceding Claims, characterised in that it contains 5 to 300 g/litre of ammonium chloride and/or 5 to 300 g/litre of ammonium sulphate as conducting salt.
7. The bath as defined in any of the preceding Claims, characterised in that it contains nicotinic acid or nicotinic acid amide as an additional glossing agent.
8. The bath as defined in Claim 7, characterised in that it contains 0.002 to 5 g/litre, preferably 0.002 to 0.005 g/litre of the glossing agent.
9. The bath as defined in any of the preceding Claims, characterised in that it contains 0.02 to 1 g/litre, preferably 0.1 g/litre of an organic phosphate ester or sulphate ester as a wetting agent.
10. The bath as defined in any of the preceding Claims, characterised in that it contains 0.01 to 1.5 g/litre of sulphite (SO₃ ^-).
11. The bath as defined in any of the preceding Claims, characterised in that it is standardised to a neutral or slightly alkaline pH value of between 6 and 8.
12. The bath as defined in Claim 11, characterised in that the pH value is standardised by the addition of ammoniac.
13. The bath as defined in Claim 11 or Claim 12, characterised in that it contains 5 to 40 g/litre of boric acid as a pH buffer.
14. The bath as defined in any of the preceding Claims, characterised in that it is standardised to a pH value of between 7 and 8.