HK1152352B - Modified copper-tin electrolyte and process for the deposition of bronze layers - Google Patents

Description

Modified copper-tin electrolyte and method for depositing bronze layer

The invention relates to a modified pyrophosphate-containing copper-tin electrolyte which is free of toxic constituents such as cyanides or sulfur-containing (thio) compounds. The invention also relates to a method for depositing decorative bronze layers on consumer and industrial articles using the electrolyte according to the invention.

The articles of daily use or daily use articles, as defined in the daily use article specification, are refined (upscale) for decorative reasons and to prevent corrosion by means of a thin, oxidation-stable metal layer. These layers must be mechanically stable and should not exhibit any discoloration or abrasion phenomena due to dullness in the case of longer-term use. Since 2001, the sale of commodities coated with nickel-containing refined alloys has been no longer permitted in europe or only possible under strict conditions, according to EUDirective 94/27/EC, because nickel and nickel-containing metal layers are contact-sensitive. In particular, bronze alloys have now been established as a substitute for nickel-containing refined layers, and these allow such mass-produced commodity products to be inexpensively refined in electrolytic barrel plating (barrel plating) or rack plating (rack plating) to produce allergen-free, track-recyclable (tracked) articles.

In the production of bronze layers for the electrolysis industry, the key properties of the layer to be produced are the brazeability of the resulting layer and its possible mechanical bond strength. For use in the art, the appearance of a layer is generally less important than its function. On the other hand, for the production of bronze layers on consumer goods, the decorative effect of the resulting layer and the long-term durability of the layer with a substantially unchanged appearance are important target parameters.

Known processes for the preparation of bronze layers include, in addition to the conventional processes using cyanide-containing and thus highly toxic alkaline baths, different electromechanical processes which, depending on the composition of their electrolyte, can generally be classified as belonging to one of two main classes of prior art: a method using an organic sulfonic acid-based electrolyte or a method using a pyrophosphate-based bath. For the purposes herein, "non-toxic" means that the electrolyte of the invention so specified does not contain a material classified as "toxic" (T) or "according to the regulations effective in europe for the treatment of hazardous and noxious substances"Very toxic "(T)⁺) Any of (1) or (ii).

For example, EP1111097a2 describes an electrolyte which, in addition to organic sulfonic acids and tin and copper ions, also contains dispersants and brighteners and optionally antioxidants. EP 1408141 a1 describes a method for the electrochemical deposition of bronze, in which an acidic electrolyte is used, which contains tin and copper ions as well as an alkylsulfonic acid and an aromatic, non-ionic wetting agent. DE

10046600A 1 describes baths containing alkyl or alkanol sulfonic acids (alkanolsulfonic acid) and soluble tin and copper salts and organic sulfur compounds and methods of using such baths.

EP1146148A2 describes a cyanide-free copper-tin electrolyte based on pyrophosphoric acid, which contains the reaction product of an amine and epichlorohydrin in a molar ratio of 1: 1 and a cationic surfactant. The amine is hexamethylenetetramine. Use of 0.5, 1.5, 2.5 and 3.0A/dm in electrodeposition²The current density of (1).

WO2004/005528 describes cyanide-free pyrophosphate-copper-tin electrolytes which contain additives composed of an amine derivative, chloropropylene oxide rings and glycidyl ether compounds in a molar ratio of from 1: 0.5 to 2: 0.1 to 5. The aim here is to obtain a broader current density range, in which a uniform deposition of the metal in a bright layer can be obtained. It is explicitly stated that such a deposition can only be obtained if the additive added consists of all three of the above-mentioned components.

Different coating methods are commonly used in the electroplating industry, depending on the functional type and nature of the part to be coated. In particular, the method differs according to the current density that can be used. Basically three different plating methods can also be mentioned.

1. Barrel plating for bulk and mass produced parts:

in this coating method, a relatively low working current density (in the order of magnitude: 0.05-0.5A/dm) is used²)。

2. Rack plating for individual parts:

in this coating method, a medium working current density (order of magnitude: 0.2-5A/dm) is used²)。

3. High speed plating of strip and wire in continuous plants:

in the electroplating field, very high operating current densities (in the order of magnitude: 5-100A/dm) are used²)。

The first two plating methods (barrel and rack) are most important for using copper-tin electroplating. Depending on the different types of electrolytes, roll-over (relatively low current density) or rack plating (medium current density) is possible.

In view of the above prior art, it was determined that such a deposition method is particularly advantageous, especially for rack plating applications: which ensures a uniform deposition of metal beyond the range of current densities normally considered and the use of electrolytes that exhibit less complexity in terms of composition.

It is therefore an object of the present invention to provide an electrolyte and a deposition method that can meet these needs. In particular, the electrolyte should be usable even at current densities which are advantageous for rack plating applications and deposit bright, luminescent layers in a uniform manner. The composition should be simpler than in the prior art, as this appears to be particularly advantageous from an economic and ecological point of view.

These objects, as well as other objects not mentioned by the present invention but evident from the prior art, are achieved by providing an electrolyte having the features of claim 1 of the present invention and its use in a deposition process as described in claim 11 of the present invention. Preferred embodiments referring back to these claims can be found in claims 2 to 10 and 12 to 16.

The object was achieved, surprisingly but still advantageously, by the provision of a non-toxic pyrophosphate-containing electrolyte for the deposition of decorative bronze alloy layers on household and industrial articles, which contains the metal to be deposited in the form of a water-soluble salt and which comprises a brightener system consisting of the reaction product of epichlorohydrin with hexamethylenetetramine and also carbonate ions or bicarbonate ions. The composition of which differs from the electrolyte of the invention of the prior art, makes it possible to obtain excellent electrolytic deposition of bronze alloys even in the medium current density range. The alloy composition remains approximately constant over a wide range of current densities, which is particularly advantageous for rack plating applications and is not obvious over the prior art.

The electrolyte in the invention contains a reaction product of epichlorohydrin and hexamethylenetetramine as brightener components. According to the invention, the additive consists exclusively of the reaction product or mixture of hexamethylenetetramine and epichlorohydrin. The molar ratio of hexamethylenetetramine to epichlorohydrin in the reaction product is preferably 1: 1-10. Particularly preferably a ratio of 1: 1.5-5 and more preferably a ratio of 1: 2-3. A ratio of 1: about 2.7 is particularly preferred. Such a product is commercially available from URSA Chemie GmbH under the name J146 (Cat. No. 33786).

The reaction product is added to the electrolyte in an amount of from 0.01ml/l to 5.0ml/l, more preferably from 0.1ml/l to 3.0ml/l, particularly preferably from 0.5 to 2.0ml/l, particularly preferably from 1.0ml/l to 1.5ml/l, based on the total solution.

The electrolyte of the present invention has a certain concentration of carbonate or bicarbonate ions. These may be added to the electrolyte in the form of soluble salts of alkali and alkaline earth metals, especially sodium or potassium carbonates or bicarbonates. However, such embodiments are preferred: wherein the metals used and to be deposited are also added to the electrolyte in whole or in part in the form of carbonates or bicarbonates. The addition of the above-mentioned salts advantageously makes it possible to adjust the concentration of carbonate or bicarbonate ions in the electrolyte, which is between 1 and 50g/l of electrolyte. The concentration is particularly preferably from 5 to 40g/l, very particularly preferably from 15 to 25 g/l.

In the electrolyte according to the invention, the metals copper and tin or copper, tin and zinc to be deposited are present in the form of their ions. They are preferably introduced in the form of water-soluble salts, preferably selected from the group consisting of pyrophosphates, carbonates, hydroxycarbonates, bicarbonates, sulfites, sulfates, phosphates, nitrites, nitrates, halides, hydroxides, oxide hydroxides, oxides and combinations thereof. Such an embodiment is particularly preferred: wherein the metal is used in the form of a salt with an ion selected from the group consisting of pyrophosphate, carbonate, hydroxycarbonate, oxide hydroxide, hydroxide and bicarbonate. The type and amount of salt introduced into the electrolyte may determine the color of the resulting decorative bronze layer and may be adjusted to the customer's requirements. As mentioned, the metal to be deposited is present in ionically dissolved form in the electrolyte for the application of decorative bronze layers on consumer and industrial goods. The ionic concentration of copper is 0.2-10g/l of electrolyte, preferably 0.3-4g/l of electrolyte, the ionic concentration of tin is 1.0-20g/l of electrolyte, preferably 2-10g/l of electrolyte, and, if present, the ionic concentration of zinc may be 1.0-20g/l of electrolyte, preferably 0-3g/l of electrolyte. In the refining of household articles, the metal to be deposited is preferably introduced in the form of pyrophosphate, carbonate or hydroxycarbonate so as to produce an ion concentration per litre of electrolyte: copper 0.3-4g, tin 2-10g and zinc 0-3g, in each case.

As mentioned, in electrochemical processes, decorative bronze layers are applied to everyday and industrial goods by using the electrolyte according to the invention. It is important here that the metal to be deposited remains in solution at all times during the treatment, whether the electrochemical coating is carried out in a continuous process or a batch process. To ensure this, the electrolyte of the present invention includes pyrophosphate as a complexing agent.

The amount of the focused phosphate ions can be adjusted in a targeted manner by the person skilled in the art. It is limited by the fact that: the concentration in the electrolyte should be higher than the minimum value in order to bring about the desired effect to a satisfactory extent. On the other hand, the amount of pyrophosphoric acid to be used is also economically guided. In this connection reference may be made to EP1146148 and the information given therein. ElectrolysisThe amount of pyrophosphate to be used in the solution is preferably 50 to 400 g/l. It is particularly preferred to use an amount of 250-350g/l electrolyte, very particularly preferably about 300g/l electrolyte. If no pyrophosphate is introduced as salt component of the metal to be deposited, it can be used as diphosphate of the alkali or alkaline earth metals or as H₂P₂O₇In combination with alkali metal or alkaline earth metal carbonates/bicarbonates. For this purpose, K is preferably used₂P₂O₇。

The pH of the electrolyte is in the range of 6-13, which is required for electroplating applications. Preferably 6 to 12, very preferably 6 to 10. It is particularly preferred to carry out the process at a pH of from 7.9 to 8.1.

The electrolyte may contain, in addition to the metal to be deposited, the pyrophosphate salt serving as complexing agent and the brightener system used, organic additives which act as brighteners, wetting agents or stabilizers. The electrolyte of the present invention may also eliminate the need for cationic surfactants. The addition of further brighteners and wetting agents is preferred only if the appearance of the decorative bronze layer to be deposited has to meet special requirements. In addition to the bronze layer color, which is mainly dependent on the proportion of the metal to be deposited, these also make it possible to adjust the brightness of the layer to the full scale between matt silk (matt silk) and high gloss. Preferably one or more compounds selected from the group consisting of monocarboxylic or dicarboxylic acids, alkanesulfonic acids, betaines and aromatic nitro compounds are added. These compounds act as stabilizers for the electrolyte bath. Particular preference is given to using oxalic acid, alkanesulfonic acids, in particular methanesulfonic acid, or nitrobenzotriazole or mixtures thereof. Suitable alkanesulfonic acids can be found in EP 1001054. For example, a possible carboxylic acid is citric acid (Jordan, Mannfred, Die galvanosche Abscheidung von Zinn und Zinnlegierung, Saulgau1993, p 156). The betaines used are preferably those which can be found in WO2004/005528 or in Jordan, Mannfred (Diaegalanische Abscheidudung von Zinn und Zinnlegierung, Saulgau1993, page 156). Particular preference is given to those described in EP 636713. In this connection, very particular preference is given to using 1- (3-sulfopropyl) pyridine betaine or 1- (3-sulfopropyl) -2-vinylpyridine betaine. Further additives can be found in the literature (Jordan, Mannfred, Die galvanosische Abscheidung von Zinn und Zinnlegierung, Saulgau 1993).

The electrolyte of the invention does not contain toxic substances classified as toxic (T) and very toxic (T +). No cyanide, no thiourea derivatives and no thiol derivatives. The non-toxic electrolyte according to the invention is very suitable for the electrochemical application of decorative bronze layers on consumer and industrial articles. It can be used for barrel plating, rack plating, belt (belt) plating or continuous conveyance plating equipment. However, it is preferably used in the rack plating process (cf. the preamble description and "PraktischeGalvanotechnik", Eugen G.Leutze Verlag 1997, page 74).

Furthermore, the invention proposes an electrolytic deposition process for the electrochemical application of decorative bronze alloy layers on household and industrial articles, in which the substrate to be coated is immersed in an electrolytic solution according to the invention. The preferred embodiments of the electrolyte discussed above apply similarly to the methods presented herein.

The process of the present invention can be operated at a temperature that will be selected by those skilled in the art based on their general technical knowledge. Preferably 20 c to 60 c, wherein the electrolyte bath is maintained during electrolysis. More preferably in the range of 30 to 50 c. It is particularly preferred to carry out the process at a temperature of about 40 ℃.

An important advantage of the present invention is that the deposition of the alloy composition does not change significantly over a wide range of current densities. This results in a surface quality that appears to be sufficiently uniform even at relatively high current densities for rack plating applications. When the concentration is 0.2A/dm²-5A/dm²When the deposition is carried out within the range, a particular alloy composition and a desired intermetallic Cu/Sn phase (. eta. + delta. phase; see: E.Raub, F.Sautter; Der Aufbau galvanoscher) can be obtainedXII， No. 11, 19578). The current density in the deposition is preferably 0.5A/dm²To 2A/dm²Particularly preferably 0.75A/dm²To 1.8A/dm²。

When using the non-toxic electrolyte of the present invention, different anodes can be used. Both soluble and insoluble anodes are suitable, and a combination of soluble and insoluble anodes is also suitable.

As a soluble anode, it is preferable to use an anode: the anode is comprised of a material selected from the group consisting of electrolytic copper, phosphorus-containing copper, tin-copper alloy, zinc-copper alloy, and zinc-tin-copper alloy. Particularly preferred are combinations of different soluble anodes composed of these materials, and combinations of soluble tin anodes with insoluble anodes.

As the insoluble anode, it is preferable to use an anode: the anode consists of a material selected from the group consisting of platinized titanium, graphite, iridium-transition metal mixed oxides and specific carbon materials ("diamond-like carbon", DLC), or a combination of these anodes. Particularly preferred are mixed oxide anodes composed of iridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide or iridium-tantalum mixed oxide. In addition, other materials can be found in Cobley, A.J., et al, (The use of insoluble antibodies in acid sulfate Copper electrochemical Solutions, Trans IMF, 2001, 79(3), pages 113 and 114).

When using soluble anodes, a particularly preferred embodiment of the method results when the substrate to be provided with a decorative bronze layer and representing the cathode is separated by an ion-exchange membrane from the insoluble anode in order to form a cathode space and an anode space. In this case, only the cathode space is filled with the non-toxic electrolyte of the present invention. The anode space preferably contains an aqueous solution containing only an electrolyte salt such as potassium pyrophosphate, potassium carbonate, potassium hydroxide, potassium bicarbonate, or mixtures thereof. This configuration prevents anodic oxidation of tin (II) ions to tin (IV) ions, which has an adverse effect in the coating process. As the ion exchange membrane, an anion or cation exchange membrane can be used. It is preferable to use a film composed of Nafion, which has a thickness of 50 to 200 μm.

Likewise, the typical current density for rack plating applications can be achieved by conventional pyrophosphate-containing electrolytes. However, the metal is not deposited with visually defect-free quality. Such electrolytes tend to form (within the customary ranges of rack plating operations) dark, striped deposits.

Only when the electrolyte of the invention is used is it possible to make it bright and the deposition of the luminescent layer in the whole current density range customary for rack plating applications. The formation of dark streaks is significantly suppressed.

The electrolyte of the invention and the process are therefore made unique by using additives formed from the combination of hexamethylenetetramine and epichlorohydrin with the carbonate or bicarbonate ions present in the electrolyte. The alloy composition and the brightness of the deposited layer are controlled in this way: in a manner that is ideal for rack plating applications. In rack plating applications, a medium current density range is important. Firstly, the combination of additives enables the alloy composition to remain approximately constant at relatively high current densities over a wide range of current densities (bronze alloys containing 40-70 wt.%, preferably 50-60 wt.% copper, and 60-30 wt.%, preferably 50-40 wt.% tin are beneficial), and secondly, a satisfactory bright and luminescent layer is obtained. Without this combination of additives, the desired alloy composition can only be obtained in a very narrow current density window, which is not useful in industrial operations. In most practical applications, the gloss and the shine of the layer are unsatisfactory without the combination of additives.

The achievement of these advantages is not obvious with respect to the prior art by means of the electrolyte according to the invention.

Examples

Plating of the test board:

base material: 0.5 and 0.75dm²A brass plate.

Coating:

0.5-2 μm copper-tin at different current densities (0.5, 1.0, 1.5 and 2.0A/dm)²) The following steps.

The experimental mechanism comprises:

the components specified for the example electrolyte were dissolved in 4l of water in a 5l glass beaker with a magnetic stirrer and the article was moved. The article to be coated is subsequently treated under the conditions indicated.

Examples electrolyte

The electrolyte for white bronze rack deposition may have the following composition:

first embodiment electrolyte

300g/l potassium pyrophosphate

20ml/l methanesulfonic acid, 70%

20g/l potassium carbonate

5.21g/l of copper (II) carbonate

8.66g/l of tin pyrophosphate

5.55g/l zinc pyrophosphate

1.25ml/l of a reaction product of hexamethylenetetramine and epichlorohydrin

Temperature: 40 deg.C

pH：7.4

Electrolyte of the second embodiment

300g/l potassium pyrophosphate

20ml/l of methanesulfonic acid

20g/l potassium carbonate

5.21g/l of copper (II) carbonate

8.66g/l of tin pyrophosphate

5.55g/l Zinc pyrophosphate

0.125ml/l reaction product (J146)

Temperature: 40 deg.C

pH：8.0

Electrolyte of the third example

100g/l potassium pyrophosphate

50ml/l methanesulfonic acid

50g/l potassium carbonate

2.0g/l copper sulfate

20g/l tin sulfate

5.0ml/l reaction product (J146)

pH：9.0

Temperature: 30 deg.C

Electrolyte of the fourth embodiment

160g/l potassium pyrophosphate

20ml/l methanesulfonic acid

5g/l sodium carbonate

4g/l basic copper carbonate

5g/l of tin pyrophosphate

0.5ml/l reaction product of hexamethylenetetramine and epichlorohydrin

pH：7.5

Temperature: 45 deg.C

Electrolyte of the fifth embodiment

200g/l potassium pyrophosphate

30ml/l Ethanesulfonic acid

50g/l citric acid

5g/l basic Potassium carbonate

3g/l copper sulphate

15g/l of tin sulfate

1ml/l reaction product of hexamethylenetetramine and epichlorohydrin

Temperature: 45 deg.C

pH：8.5

The layers were evaluated by:

a) visual appearance

b) Measurement of gloss and Brightness

c) Measurement of alloy composition (the higher the content of copper, the darker the layer)

d) Darkening test, Corrosion test

As a result:

a) visual appearance:

the deposited layer is uniformly luminous and shiny.

b) Luminance value (L)^＊A value; tested by the CIE LAB method; http:// www.cielab.de /)

Comparison of "example electrolyte 2" with "prior art

c) Alloy composition

Comparison of "example electrolyte 2" with "prior art

The higher copper content in the layer results in a darker color of the coating and tends to produce a poorer darkening behavior.

Claims (16)

1. A non-toxic pyrophosphate-containing electrolyte for the deposition of decorative bronze alloy layers on consumer goods and industrial articles, which contains the metal to be deposited in the form of a water-soluble compound, wherein the electrolyte comprises a brightener system and carbonate or bicarbonate ions, wherein the brightener system consists of the reaction product of epichlorohydrin with hexamethylenetetramine, wherein the water-soluble compound is selected from the group consisting of pyrophosphates, carbonates, hydroxycarbonates, bicarbonates, sulfites, sulfates, phosphates, nitrites, nitrates, halides, hydroxides, oxide hydroxides, oxides and mixtures thereof.

2. The electrolyte of claim 1 wherein the reaction product has a molar ratio of hexamethylenetetramine to epichlorohydrin of 1: 1 to 1: 10, but excluding 1: 1.

3. The electrolyte as claimed in claim 2, wherein the amount of the reaction product used is 0.01 to 5 ml/l.

4. The electrolyte of claim 1 wherein the carbonate or bicarbonate ions are present in an amount of 1-50 g/l.

5. The electrolyte as claimed in any of claims 1 to 4, wherein the electrolyte comprises copper and tin or copper, tin and zinc as the metal to be deposited.

6. The electrolyte as claimed in claim 5, wherein the metal to be deposited is present in ionically dissolved form, the ionic concentration of copper being from 0.2 to 10g/l and the ionic concentration of tin being from 1.0 to 20 g/l.

7. The electrolyte as claimed in claim 5, wherein the metal to be deposited is present in ionically dissolved form, the ionic concentration of copper being 0.2 to 10g/l, the ionic concentration of tin being 1.0 to 20g/l and the ionic concentration of zinc being 1.0 to 20 g/l.

8. The electrolyte of claim 1, wherein the amount of pyrophosphate in the electrolyte is 50-400 g/l.

9. The electrolyte of claim 1, wherein the electrolyte has a pH of 6 to 13.

10. The electrolyte as claimed in claim 1, wherein one or more compounds having a stabilizing action are present, selected from the group consisting of monocarboxylic and dicarboxylic acids, alkanesulfonic acids, betaines and aromatic nitro compounds.

11. An electrodeposition process for electrochemically applying a decorative bronze alloy layer to everyday objects and industrial articles, wherein a substrate to be coated is immersed in an electrolyte as claimed in any one of claims 1 to 9.

12. A method as claimed in claim 11, wherein the electrolyte is maintained at a temperature in the range 20 to 60 ℃.

13. The method of claim 11, wherein the current density is adjusted to 0.2 to 5 amps/square decimeter.

14. The method of claim 11, wherein a soluble anode is used, the anode being composed of a material selected from electrolytic copper, phosphorus-containing copper, tin-copper alloy, zinc-copper alloy and zinc-tin-copper alloy, or a combination of these anodes.

15. The method of claim 11, wherein an insoluble anode is used, which anode is composed of a material selected from the group consisting of platinized titanium, graphite, iridium-transition metal mixed oxide, and diamond-like carbon, or a combination of these anodes.

16. The method of claim 11, wherein the cathode and the insoluble anode are spaced apart from each other by an ion exchange membrane to form a cathode space and an anode space, and only the cathode space contains the non-toxic electrolyte such that Sn is²⁺To Sn⁴⁺Is inhibited.