A WATER-BASED COMPOSITION FOR POST-TREATMENT OF METAL SURFACES

Description

Field of the Invention

[0001] The present invention relates to a water-based composition for post-treatment of metal surfaces, the use thereof and to a method for post-treatment of metal surfaces.

Background of the Invention

[0002] Silver and silver alloys are used in electronic devices but it is inevitable that finished articles will require further cleaning and polishing to temporarily remove undesired tarnish products. It is well-known that with exposure to everyday atmospheric conditions, silver and silver alloys develop a lustre-destroying dark film known as tarnish. Prevention of tarnishing of metals and metal alloys is a challenging problem in numerous industries. The tarnishing of metal and metal alloys has been especially problematic in the electronic materials industry where tarnishing may lead to faulty electrical contact between components in electronic devices.

[0003] US20070277906A1 discloses for use in treating a metal, e.g. silver or an alloy of silver, a water-based composition comprising a treatment agent selected from an alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide and at least one of an amphoteric, nonionic or cationic surfactant in a concentration that is effective to solubilise the treatment agent. Preferably the composition comprises at least a non-ionic relatively hydrophobic surfactant e.g. cocamide DEA. The composition is particularly suitable for the treatment of Ag-Cu-Ge alloys.

Objectives of the Invention

[0004] The objective of the present invention was to provide a composition for effective post-treatment of metal surfaces, particularly silver or silver alloys, in order to prevent tarnishing of such surfaces.

Summary and Detailed Description of the Invention

[0005] The invention provides with a water-based composition for post-treatment of metal surfaces, preferably a silver or silver alloy surface, according to claim 1, the use thereof according to claim 12 and a method according to claim 13. Preferred embodiments are described within the dependent claims.

[0006] The metal surfaces are especially surfaces in the field of technical and decorative surfaces either on metal substrates or plastic materials, e.g. on connectors or IC / leadframe applications as well as surfaces on automotive, aerospace, construction, communication, furniture, sanitary and consumer goods.

[0007] The invention provides with a water-based composition for post-treatment of metal surfaces, preferably a silver or silver alloy surface comprising:

an alkanethiol,

an anionic, cationic, non-ionic, amphoteric or zwitterionic surfactant with a HLB value of 12 to 18, preferably 15,

wherein the water-based composition further contains

a compound of the general formula I:

wherein

R₁ is -H, -CH₃, -C₂H₅, -(C₂H₄O)_p-H, -(C₂H₄O)_p-CH₃, -(C₂H₄O)_p-CH(CH₃)₂, -(C₂H₄O)_p-C(CH₃)₃, wherein p is an integer in the range of 1 to 20, preferably 1 to 10, more preferably 2 to 6,

R₂ is H or CH₃, preferably CH₃,

n is an integer in the range of 0 to 3, preferably 1 to 3, even more preferably 1 or 2,

m is an integer in the range of 0, 1 or 2, preferably 0.

[0008] According to claim 1 the HLB values were determined according to the method of W.C. Griffin.

[0009] With the present invention, in general or one of the following further embodiments, one or more of the following benefits are obtained:

• enhancing of anti-tarnish properties (particularly proven by K₂S test)
• transparent protective coating provides a highly hydrophobic surface property
• repelling oxidation agents
• transparent composition, prevention of negative effects on appearance of a surface treated with the composition
• enhanced formation of a self-assembled thiol monolayer onto immersed silver surfaces, thereby providing with a non-polar film
• improved rinsing capability of hydrophobic alkanethiol rests after silver surfaces treatment, effective elimination of oily residues

[0010] The composition can be an emulsion.

[0011] The alkanethiol forms a self-assembled thiol monolayer onto immersed silver surfaces which prevents or retards tarnishing.

[0012] The compound of formula I is also called a "gemini surfactant" which has the more general, following structure:

[0013] Gemini surfactants are composed of two polar heads (hydrophilic groups) flanked by a spacer to which hydrophobic tails are linked; the spacer can be rigid or flexible, polar or apolar. The invention also discloses using such general surfactants in a composition for post-treatment of metal surfaces. It has been shown that by addition of a surfactant with above structure, particularly by addition of a component of formula I, improved anti tarnishing properties of the composition can be reached.

[0014] In a preferred embodiment of the compound of formula I is m = 0, n in the range of 0 to 3, preferably n in the range of 1 to 3, more preferably n is 1 or 2, and R₁ is independently selected from the group consisting of R₁ is -H, -CH₃, -C₂H₅ and -(C₂H₄O)_p-H with p in the range 2 to 6.

[0015] More preferred the compound of formula I is selected from the group consisting of 2,3,6,7-tetramethyl-4-octyne-3,6-diol, 2,5,8,11-tetramethyl-6-dodecyn-5,8-diol ethoxylate, 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,2'-[(2,4,7,9-tetramethyl-5-decyne-4,7-diyl) bis(oxy)] diethanol, and 2,4,7,9-tetramethyl-5-decyne-4,7-diolbispolyoxyethylene-ether.

[0016] The anionic, cationic, non-ionic, amphoteric or zwitterionic surfactant may have a hydrophobic tail that may linear or branched.

[0017] The anionic, cationic, non-ionic, amphoteric or zwitterionic surfactant may be an ethoxylated or propoxylated alkyl, ethoxylated or propoxylated amine, ethoxylated or propoxylated amide, ethoxylated or propoxylated alcohol, or a mixture thereof. A beneficial surfactant is 3-ethoxy-2-methylnonane.

[0018] The surfactant may have the general formula II:

        R₃O(CH₂CH₂O)_xH     formula II

wherein

R₃ is a linear or branched alkyl group, having 6 - 15 carbon atoms, preferably 8-12 carbon atoms,

x is an integer in the range of 3 - 15, preferably 7 - 11.

[0019] Preferably the surfactant is a polyethylene glycol, more preferably PEG-11 C10-11 Oxo alcohol ethoxylate (CAS Nr: 78330-20-8).

[0020] The water-based composition may comprise a co-emulgator, which can also be called a "second surfactant".

[0021] The co-emulgator may have the general formula III

        R₄O(CH₂CH₂O)_yH     formula III

wherein

R₄ is a linear or branched alkyl group, having 16 - 20 carbon atoms, preferably 16-18 carbon atoms,

y is an integer in the range of 2 - 10, preferably 3 - 6.

[0022] The co-emulgator is preferably polyalkylene glycol ether. Preferably the co-emulgator is an Alcohol C16-18 ethoxylated propoxylated, (CAS Nr. 68002-96-0).

[0023] The alkanethiol is preferably a branched or unbranched C₁₀- to C₂₀-alkanethiol, more preferred unbranched C₁₀- to C₂₀-alkanethiol, e.g. decanthiol, undecanthiol, dodecanthiol, hexadecanthiol, heptadecanthiol, octadecanthiol, nonadecanthiol, eicosanthiol, most preferably heptadecanthiol, octadecanthiol, nonadecanthiol, eicosanthiol. In one preferred embodiment alkanethiol is octadecanthiol.

[0024] In a preferred embodiment, the water-based composition is free of chromate and/or free of organic solvent.

[0025] The water-based composition may have a pH in the range of 1 to 6, preferably 2 to 4. The pH may be adjusted by a buffer system. Suitable buffer systems are citric acid / citrate, acetic acid / acetate, tartaric acid / tartrate, phosphoric acid / phosphate or any suitable acid and salts combinations.

[0026] The water-based composition may comprise the mentioned constituents in following amounts:

alkanethiol:	0.1 - 5 g/L, preferably 0.5 - 4 g/L
surfactant:	2 - 30 g/L, preferably 5 - 20 g/L
compound of formula I:	1 - 10 g/L, preferably 1 - 5 g/L; and
optionally Co-emulgator:	0.1 - 5 g/L, preferably 0.5 - 2 g/L

[0027] In another aspect, the invention is directed to the use of the water-based composition above for post-treatment of metal surface, particularly a silver or silver alloy surface, to avoid tarnishing after metal deposition, particularly after silver or silver alloy deposition.

[0028] In still another aspect, the invention is directed to a method for post-treatment of a metal surface, particularly a silver or silver alloy surface comprising, in this order, the steps:

a. providing a metal surface, particularly a silver or silver alloy surface,

b. contacting the metal surface, particularly the silver or silver alloy surface, with the water-based composition as described before. Any of the water-based compositions that were described before can be employed.

[0029] Contacting can be done by any suitable method. The contacting in step b. may particularly be done by immersing into the water-based composition and/or by spraying with the water-based-composition onto the surface.

[0030] Contacting in step b. may be done additionally under electroless conditions, i.e. without supplying a current between the metal surface and an electrode.

[0031] In another embodiment, contacting in step b. takes place under applying an electrical current between the metal surface, particularly the silver or silver alloy surface, and at least one electrode when the metal surface is immersed into the water-based composition. The metal surface can act as cathode and the other electrode (which is the counter electrode) can act as anode, or vice versa. Preferably the metal surface is cathodic.

[0032] The present invention works preferably with a composition temperature in a range of room temperature (22±2°C) or higher, more preferably 30 °C or higher, most preferably in a range of 35 - 65 °C.

EXAMPLES

[0033] Hereinafter, the invention is illustrated by working examples.

Inventive Example 1:

[0034] Water-based compositions were provided, wherein the concentrations of c.) compound of the general formula I (compound c1)), vary while the concentrations of other components are fixed, respectively.

[0035] The water-based composition was made by dissolving the following components in water:

a. alkanethiol: octadecanthiol. (CAS Nr. 2885-00-9) amount: 2,5 g/L

b. surfactant: PEG-11 C10-11 Oxo alcohol ethoxylates (CAS Nr: 78330-20-8) amount: 17,5 g/l

c. compound of the general formula I: c1) 2,5,8,11-Tetramethyl-6-dodecyn-5,8-diol ethoxylate, (CAS Nr. 169117-72-0) in an amount: 2, 3 or 4 g/l

d. co-emulgator: Alcohol C16-18 polyalkylene glycol ether, (CAS Nr. 68002-96-0) amount: 2,5 g/L.

Inventive Example 2:

[0036] Water-based composition was provided wherein the following compound c2) 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate (CAS Nr. 9014-85-1) and c3) 2,4,7,9-tetramethyl-5-decyne-4,7-diol (CAS Nr. 126-86-3) of c.) compound of the general formula I were separately used at same concentrations:
The water-based composition was made by dissolving the following components in water:

a. alkanethiol: octadecanthiol. (CAS Nr. 2885-00-9) amount: 2,5 g/L

b. surfactant: PEG-11 C10-11 Oxo alcohol ethoxylates (CAS Nr: 78330-20-8) amount: 17,5 g/l

c. compound of the general formula I (c2 or c3): amount: 2 g/l

d. co-emulgator: Alcohol C16-18 polyalkylene glycol ether, (CAS Nr. 68002-96-0) amount: 2,5 g/L.

Comparative Example:

[0037] Comparative water-based compositions were provided, comprising a., b. and d. wherein the concentrations of compound of the general formula I (c1-c3) was zero and the other concentrations were as stated above.

1. Methods

[0038] The post-treatment was performed on silver plated copper panels. These panels, having a copper surface, may be provided from the following steps:

▪ Providing copper panels

1. Degrease Uniclean™ 260 (electrophoretic alkaline cleaner) cathodic 7V / 45°C / 30 sec

2. Activate: Uniclean™ 675 (mild acidic activator)immersion / RT / 30 sec

3. Pre-silver Pre-silver (low silver concentrated solution) cathodic 3V / RT / 15 sec

4. Silver Silverlume Plus (bright silver deposition solution) cathodic 1 ASD / RT / 5 min
or AgO-56 (technical silver deposition solution) cathodic 1 ASD / RT / 5 min
or Argalux™ NC mod. (cyanid-free bright silver deposition solution) cathodic 0.8 ASD / RT / 5 min

wherein RT is room temperature between 22±2°C; DI water is deionized water; ASD is Ampere per square decimeter A/dm² and V is volt/voltage.

[0039] In the sense of this invention the post-treatment composition may work also with otherwise obtained silver plated surfaces in the field of use of technical or decorative (with or without cyanide) silver deposition solutions for silver plating to avoid tarnishing after this silver plating.

[0040] The inventive water-based compositions according to the invention for post-treatment and the comparative water-based compositions were used under various conditions (see tests below).

[0041] After post-treatment in the water-based composition all samples were rinsed with:

• Hot DI water rinse,
• Cold DI water rinse and
• dried with compressed air.

  ▪ Optical evaluation after post-treatment with the inventive and comparative composition and subsequent sulphide test due to:

  • Residues immediately after post-treatment and rinse
  • Colorations and tarnishing after sulphide test

[0042] The observations have been carried out without any instruments by skilled person.

▪ Sulphide test

▪ Material: Glass beaker

▪ Chemicals: Potassium Sulphide 44% K₂S, 2% w/w in water

▪ Temperature: 22 ± 2°C

▪ Dipping time: 5 - 10 min

▪ Evaluation by the skilled person

▪ according to colour intensity

2. Results

2.1 Rinsing capability test

[0043] The inventive water-based compositions showed improved rinsing capability in comparison with the comparative water-based compositions and eliminate oily residues issues completely. The treatment of Silverlume Plus, AgO-56 and Argalux™ NC mod. plated silver surfaces with the comparative water-based compositions the surfaces showed poor rinsing capability, whereas the inventive water-based compositions show very good rinsing capability.

2.2 Anti tarnishing tests

[0044] The inventive water-based compositions showed improved anti-tarnish protection in comparison with the comparative water-based compositions without the compound of the general formula I (c1-c3). The not-treated silver surfaces obtained from silver plating solutions as Silverlume Plus, AgO-56 and Argalux™ NC mod. exhibit very poor anti-tarnish protection. These plated silver surfaces treated with the comparative water-based compositions showed less discoloration after sulphide test, whereas the surfaces treated with the inventive water-based compositions show few to no discoloration.

Test material: bright silver plated surface (Silverlume Plus)

[0045] Water-based composition conditions: pH 2.5 - Temperature 55°C - agitation 200 RPM - immersion process for 1 min, rinse & dry.

Test material: bright decorative silver layer (Silverlume Plus)
Compound of formula I	0 g/L (comparative example)	2 g/L (c1-c3)	3 g/L (c1)	4 g/L (c1)
Residues	Very poor (many residues)	Excellent (none)	Excellent (none)	Excellent (none)
Anti-tarnish (after 5 min into K2S 2%)	Very poor (dark discoloration)	Improved (yellow discoloration)	Strongly improved (Yellow to no discoloration)	Excellent (no discoloration)

[0046] Test material: bright silver plated surface (Argalux NC™ mod), cyanide free Water-based composition conditions: pH 2.5 - Temperature 55°C - Agitation 200 RPM - 1 min immersion process, rinse & dry.

Test material: bright silver cyanide free (Argalux NC™ mod.)
Compound (c1) of formula I	0 g/L (comparative example)	3 g/L	4 g/L
Residues	Poor (many)	Excellent (none)	Excellent (none)
Anti-tarnish (after 5 min into K2S 2%)	Very poor (dark colored)	Strongly improved (yellow colored)	Excellent (no discoloration)

Test material: technical silver plated surface (AgO-56™)

[0047] Water-based composition conditions: pH 2.5 - Temperature 55°C - agitation 200 RPM - immersion process for 1 min, rinse & dry.

Test material: technical silver (AgO-56 ™)
Compound (c1) of formula I	0 g/L (comparative example)	3 g/L	4 g/L
Residues	Poor (many)	Excellent (none)	Excellent (none)
Anti-tarnish (after 5 min into K2S 2%)	Very poor (dark colored)	Strongly improved (yellow to no discoloration)	Excellent (no discoloration)

2.3 Cathodic use

Test material: technical silver plated surface (AgO-56™)

[0048] Water-based composition conditions: pH 2.5 - Temperature 55°C - Agitation 200 RPM - immersion for 1 min or cathodic 0.5 A/dm² for 1 min, rinse & dry

Test material: technical silver (AgO-56 ™)
Compound (c1) of formula I	0 g/L (comparative example)		3 g/L
Process	Immersion	Cathodic	Immersion	Cathodic
Residues	Poor (many)	Poor (many)	Excellent (none)	Excellent (none)
Anti-tarnish (dipping time into K2S 2%)	5 min	10 min	5 min	10 min
	Very poor (dark colored)	Strongly improved	Good (yellow to no discoloration)	Excellent (no discoloration)

3. Conclusions

[0049] 

▪ The inventive water-based compositions do improve:

• The wettability of immersed metal surfaces, especially silver.
• The formation of a self-assembled thiol monolayer onto immersed silver surfaces, making a non-polar film and enhancing anti-tarnish properties.
• The rinsing of hydrophobic alkanethiol rests after silver surfaces treatment with water based solution of the invention.

▪ Immersion and electrophoretic uses are suitable in avoiding tarnishing of the metal plated surfaces after metal plating.

Claims

1. A water-based composition for post-treatment of metal surfaces, preferably a silver or silver alloy surface, comprising
an alkanethiol,
an anionic, cationic, non-ionic, amphoteric or zwitterionic surfactant with a HLB value of 12 to 18,
characterized in that the water-based composition further contains
a compound of the general formula I:

wherein

R₁ is -H, -CH₃, -C₂H₅, -(C₂H₄O)_p-H, -(C₂H₄O)_p-CH₃, -(C₂H₄O)_p-CH(CH₃)₂, -(C₂H₄O)_p-C(CH₃)₃, wherein p is an integer in the range of 1 to 20,

R₂ is H or CH₃,

n is an integer in the range of 0 to 3,

m is an integer in the range of 0, 1 or 2

wherein the HLB values were determined according to the method of W.C. Griffin.

2. The water-based composition according to claim 1, wherein in the compound of formula I is m = 0, n in the range of 0 to 3 and R₁ is independently selected from the group consisting of -H, -CH₃, -C₂H₅ and -(C₂H₄O)_p-H wherein p in the range 2 to 6.

3. The water-based composition according to claim 1, wherein the compound of formula I is selected from the group consisting of 2,3,6,7-tetramethyl-4-octyne-3,6-diol, 2,5,8,11-tetramethyl-6-dodecyn-5,8-diol ethoxylate, 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate, 2,4,7,9-tetramethyl-5-decyne-4,7-diol-bispolyoxyethyleneether, and 2,4,7,9-tetramethyl-5-decyne-4,7-diol.

4. The water-based composition according to any of the foregoing claims, wherein the surfactant is an ethoxylated or propoxylated alkyl, ethoxylated or propoxylated amine, ethoxylated or propoxylated amide, ethoxylated or propoxylated alcohol, or a mixture thereof.

5. The water-based composition according to any of the foregoing claims, wherein the surfactant has the general formula II

        R₃O(CH₂CH₂O)_xH     (II)

wherein

R₃ is a linear or branched alkyl group, having 6 - 15 carbon atoms, preferably 8-12 carbon atoms,

x is an integer in the range of 3 - 15, preferably 7 - 11.

6. The water-based composition according to any of the foregoing claims, wherein the alkanethiol is a C₁₀- to C₂₀-alkanethiol.

7. The water-based composition according to any of the foregoing claims, wherein the composition comprises a co-emulgator

8. The water-based composition according to claim 7, wherein the co-emulgator has the general formula III

        R₄O(CH₂CH₂O)_yH     (III)

wherein

R4 is a linear or branched alkyl group, having 16 - 20 carbon atoms, preferably 16-18 carbon atoms,

y is an integer in the range of 2 - 10, preferably 3 - 6.

9. The water-based composition according to claim 7 or 8, wherein the co-emulgator is a polyalkylene glycol ether.

10. The water-based composition according to any of the foregoing claims, wherein the composition is free of chromate and/or free of organic solvent.

11. The water-based composition according to any of the foregoing claims, having a pH in the range of 1 to 10.

12. The use of the water-based composition according to one of the foregoing claims 1 - 10 for post-treatment of metal surface, particularly a silver or silver alloy surface, to avoid metal tarnishing.

13. A method for post-treatment of a metal surface, particularly a silver or silver alloy surface comprising, in this order, the steps

a. providing a metal surface, particularly a silver or silver alloy surface,

b. contacting the metal surface, particularly the silver or silver alloy surface, with a water-based composition according to any of claims 1 - 11.

14. The method according to claim 13, wherein the contacting in step b. is applied as immersing and/or per spraying and/or per any other suitable method allowing the contact between the metal and the claim solution.

15. The method according to claim 13 or 14, wherein the contacting in step b. takes place under applying an electrical current between the metal surface, particularly the silver or silver alloy surface, and at least one electrode when the metal is immersed into the claim solution.

Ansprüche

1. Wasserbasierte Zusammensetzung zur Nachbehandlung von Metalloberflächen, vorzugsweise einer Silber- oder Silberlegierungsoberfläche, umfassend
ein Alkanthiol,
ein anionisches, kationisches, nichtionisches, amphoteres oder zwitterionisches Tensid mit einem HLB-Wert von 12 bis 18,
dadurch gekennzeichnet, dass die wasserbasierte Zusammensetzung ferner
eine Verbindung der allgemeinen Formel I:

enthält, wobei

R₁ für -H, -CH₃, -C₂H₅, - (C₂H₄O)_p-H, - (C₂H₄O)_p-CH₃, - (C₂H₄O)_p-CH(CH₃)₂ oder -(C₂H₄O)_p-C(CH₃)₃ steht, wobei p für eine ganze Zahl im Bereich von 1 bis 20 steht,

R₂ für H oder CH₃ steht,

n für eine ganze Zahl im Bereich von 0 bis 3 steht,

m für eine ganze Zahl im Bereich von 0, 1 oder 2 steht, wobei die HLB-Werte nach der Methode von W. C. Griffin bestimmt wurden.

2. Wasserbasierte Zusammensetzung nach Anspruch 1, wobei in der Verbindung der Formel I m = 0 ist, n im Bereich von 0 bis 3 liegt und R₁ unabhängig aus der Gruppe bestehend aus -H, -CH₃, -C₂H₅ und - (C₂H₄O)_p-H ausgewählt ist, wobei p im Bereich von 2 bis 6 liegt.

3. Wasserbasierte Zusammensetzung nach Anspruch 1, wobei die Verbindung der Formel I aus der Gruppe bestehend aus 2,3,6,7-Tetramethyl-4-octin-3,6-diol, 2,5,8,11-Tetramethyl-6-dodecin-5,8-diolethoxylat, 2,4,7,9-Tetramethyl-5-decin-4,7-diolethoxylat, 2,4,7,9-Tetramethyl-5-decin-4,7-diol-bispolyoxyethylenether und 2,4,7,9-Tetramethyl-5-decin-4,7-diol ausgewählt ist.

4. Wasserbasierte Zusammensetzung nach einem der vorhergehenden Ansprüche, wobei es sich bei dem Tensid um ein ethoxyliertes oder propoxyliertes Alkyl, ein ethoxyliertes oder propoxyliertes Amin, ein ethoxyliertes oder propoxyliertes Amid, einen ethoxylierten oder propoxylierten Alkohol oder eine Mischung davon handelt.

5. Wasserbasierte Zusammensetzung nach einem der vorhergehenden Ansprüche, wobei das Tensid die allgemeine Formel II

        R₃O(CH₂CH₂O)_xH     (II)

aufweist, wobei

R₃ für eine lineare oder verzweigte Alkylgruppe mit 6-15 Kohlenstoffatomen, vorzugsweise 8-12 Kohlenstoffatomen, steht,

x für eine ganze Zahl im Bereich von 3-15, vorzugsweise 7-11, steht.

6. Wasserbasierte Zusammensetzung nach einem der vorhergehenden Ansprüche, wobei es sich bei dem Alkanthiol um ein C₁₀- bis C₂₀-Alkanthiol handelt.

7. Wasserbasierte Zusammensetzung nach einem der vorhergehenden Ansprüche, wobei die Zusammensetzung einen Coemulgator umfasst.

8. Wasserbasierte Zusammensetzung nach Anspruch 7, wobei der Coemulgator die allgemeine Formel III

        R₄O(CH₂CH₂O)_yH     (III)

aufweist, wobei

R₄ für eine lineare oder verzweigte Alkylgruppe mit 16-20 Kohlenstoffatomen, vorzugsweise 16-18 Kohlenstoffatomen, steht,

y für eine ganze Zahl im Bereich von 2-10, vorzugsweise 3-6, steht.

9. Wasserbasierte Zusammensetzung nach Anspruch 7 oder 8, wobei es sich bei dem Coemulgator um einen Polyalkylenglykolether handelt.

10. Wasserbasierte Zusammensetzung nach einem der vorhergehenden Ansprüche, wobei die Zusammensetzung frei von Chromat und/oder frei von organischem Lösungsmittel ist.

11. Wasserbasierte Zusammensetzung nach einem der vorhergehenden Ansprüche mit einem pH-Wert im Bereich von 1 bis 10.

12. Verwendung der wasserbasierten Zusammensetzung nach einem der vorhergehenden Ansprüche 1-10 zur Nachbehandlung einer Metalloberfläche, insbesondere einer Silber- oder Silberlegierungsoberfläche, zur Vermeidung des Anlaufens des Metalls.

13. Verfahren zur Nachbehandlung einer Metalloberfläche, insbesondere einer Silber- oder Silberlegierungsoberfläche, das die folgenden Schritte in der angegebenen Reihenfolge umfasst:

a. Bereitstellung einer Metalloberfläche, insbesondere einer Silber- oder Silberlegierungsoberfläche,

b. Inkontaktbringen der Metalloberfläche, insbesondere der Silber- oder Silberlegierungsoberfläche, mit einer wasserbasierten Zusammensetzung nach einem der Ansprüche 1-11.

14. Verfahren nach Anspruch 13, bei dem das Inkontaktbringen in Schritt b. als Eintauchen und/oder durch Sprühen und/oder durch ein anderes geeignetes Verfahren, das den Kontakt zwischen dem Metall und der beanspruchten Lösung erlaubt, durchgeführt wird.

15. Verfahren nach Anspruch 13 oder 14, wobei das Inkontaktbringen in Schritt b. unter Anlegen eines elektrischen Stroms zwischen der Metalloberfläche, insbesondere der Silber- oder Silberlegierungsoberfläche, und mindestens einer Elektrode stattfindet, wenn das Metall in die beanspruchte Lösung eingetaucht ist.

Revendications

1. Composition à base d'eau pour le post-traitement de surfaces métalliques, préférablement une surface en argent ou en alliage d'argent, comprenant un alcanethiol,
un tensioactif anionique, cationique, non ionique, amphotère ou zwittérionique ayant une valeur d'équilibre hydrophile/lipophile de 12 à 18, caractérisée en ce que la composition à base d'eau contient en outre
un composé ayant la formule générale I :

dans laquelle

R₁ est un groupe -H, -CH₃, -C₂H₅, -(C₂H₄O)_p-H,-(C₂H₄O)_p-CH₃, -(C₂H₄O)_p-CH(CH₃)₂, -(C₂H₄O)_p-C(CH₃)₃, dans lequel p est un nombre entier de 1 à 20,

R₂ est un atome d'hydrogène ou un groupe CH₃,

n est un nombre entier de 0 à 3,

m est un nombre entier de 0, 1 ou 2,

dans laquelle les valeurs d'équilibre hydrophile/lipophile ont été déterminées selon la méthode de W.C. Griffin.

2. Composition à base d'eau selon la revendication 1, dans laquelle, dans le composé ayant la formule I, m = 0, n vaut de 0 à 3 et R₁ est sélectionné indépendamment dans le groupe constitué de groupes -H, -CH₃, -C₂H₅ et - (C₂H₄O)_p-H dans lequel p vaut de 2 à 6.

3. Composition à base d'eau selon la revendication 1, dans laquelle le composé ayant la formule I est sélectionné dans le groupe constitué du 2,3,6,7-tétraméthyl-4-octyne-3,6-diol, de l'éthoxylate de 2,5,8,11-tétraméthyl-6-dodécyn-5,8-diol, de l'éthoxylate de 2,4,7,9-tétraméthyl-5-décyne-4,7-diol, du 2,4,7,9-tétraméthyl-5-décyne-4,7-diol-bispolyoxyéthylèneéther, et du 2,4,7,9-tétraméthyl-5-décyne-4,7-diol.

4. Composition à base d'eau selon l'une quelconque des revendications précédentes, dans laquelle le tensioactif est un alkyle éthoxylé ou propoxylé, une aminé éthoxylée ou propoxylée, un amide éthoxylé ou propoxylé, un alcool éthoxylé ou propoxylé, ou un mélange de ceux-ci.

5. Composition à base d'eau selon l'une quelconque des revendications précédentes, dans laquelle le tensioactif a la formule générale II

        R₃O(CH₂CH₂O)_xH     (II)

dans laquelle

R₃ est un groupe alkyle linéaire ou ramifié, comportant 6 à 15 atomes de carbone, préférablement 8 à 12 atomes de carbone,

x est un nombre entier de 3 à 15, préférablement de 7 à 11.

6. Composition à base d'eau selon l'une quelconque des revendications précédentes, dans laquelle l'alcanethiol est un alcanethiol C₁₀-C₂₀.

7. Composition à base d'eau selon l'une quelconque des revendications précédentes, la composition comprenant un co-émulsionnant.

8. Composition à base d'eau selon la revendication 7, dans laquelle le co-émulsionnant a la formule générale III

        R₄O(CH₂CH₂O)_yH     (III)

dans laquelle

R₄ est un groupe alkyle linéaire ou ramifié, comportant 16 à 20 atomes de carbone, préférablement 16 à 18 atomes de carbone,

y est un nombre entier de 2 à 10, préférablement de 3 à 6.

9. Composition à base d'eau selon la revendication 7 ou 8, dans laquelle le co-émulsionnant est un éther de polyalkylène glycol.

10. Composition à base d'eau selon l'une quelconque des revendications précédentes, la composition étant sans chromate et/ou sans solvant organique.

11. Composition à base d'eau selon l'une quelconque des revendications précédentes, ayant un pH de 1 à 10.

12. Utilisation de la composition à base d'eau selon l'une quelconque des revendications précédentes 1 à 10 pour le post-traitement d'une surface métallique, en particulier une surface en argent ou en alliage d'argent, pour éviter le ternissement du métal.

13. Procédé de post-traitement d'une surface métallique, en particulier une surface en argent ou en alliage d'argent, comprenant, dans cet ordre, les étapes qui consistent à :

a. fournir une surface métallique, en particulier une surface en argent ou en alliage d'argent,

b. mettre en contact la surface métallique, en particulier la surface en argent ou en alliage d'argent, avec une composition à base d'eau selon l'une quelconque des revendications 1 à 11.

14. Procédé selon la revendication 13, dans lequel la mise en contact à l'étape b. est réalisée sous la forme d'une immersion et/ou par pulvérisation et/ou par tout autre procédé convenant à cette fin permettant une mise en contact du métal et de la solution selon les revendications.

15. Procédé selon la revendication 13 ou 14, dans lequel la mise en contact à l'étape b. a lieu tandis qu'un courant électrique est appliqué entre la surface métallique, en particulier la surface en argent ou en alliage d'argent, et au moins une électrode quand le métal est immergé dans la solution selon les revendications.