Patent Publication Number: US-2019177859-A1

Title: A water-based composition for post-treatment of metal surfaces

Description:
FIELD OF THE INVENTION 
     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 
     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. 
     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 
     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 
     The invention provides with a water-based composition for post-treatment of metal surfaces, preferably a silver or silver alloy surface, the use thereof and a method. Preferred embodiments are described within the dependent claims. 
     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/lead frame applications as well as surfaces on automotive, aerospace, construction, communication, furniture, sanitary and consumer goods. 
     The invention in particularly 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
 
R 1  is —H, —CH 3 , —C 2 H 5 , —(C 2 H 4 O) p —H, —(C 2 H 4 O) p —CH 3 , —(C 2 H 4 O) p —CH(CH 3 ) 2 , —(C 2 H 4 O) p —C(CH 3 ) 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 CH 3 , preferably CH 3 ,
 
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.
 
     HLB values were determined according to the method of W. C. Griffin. 
     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 K 2 S 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       

     The composition can be an emulsion. 
     The alkanethiol forms a self-assembled thiol monolayer onto immersed silver surfaces which prevents or retards tarnishing. 
     The compound of formula I is also called a “gemini surfactant” which has the more general, following structure: 
     
       
         
         
             
             
         
       
     
     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. 
     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 R 1  is independently selected from the group consisting of R 1  is —H, —CH 3 , —C 2 H 5  and —(C 2 H 4 O) p —H with p in the range 2 to 6. 
     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. 
     The anionic, cationic, non-ionic, amphoteric or zwitterionic surfactant may have a hydrophobic tail that may linear or branched. 
     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. 
     The surfactant may have the general formula II: 
       R 3 O(CH 2 CH 2 O) x H   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.
 
     Preferably the surfactant is a polyethylene glycol, more preferably PEG-11 C10-11 Oxo alcohol ethoxylate (CAS Nr: 78330-20-8). 
     The water-based composition may comprise a co-emulsifier, which can also be called a “second surfactant”. 
     The co-emulsifier may have the general formula III 
       R 4 O(CH 2 CH 2 O) y H   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.
 
     The co-emulsifier is preferably polyalkylene glycol ether. Preferably the co-emulsifier is an Alcohol C16-18 ethoxylated propoxylated, (CAS Nr. 68002-96-0). 
     The alkanethiol is preferably a branched or unbranched C 10  - to C 20 -alkanethiol, more preferred unbranched C 10 - to C 20 -alkanethiol, e.g. decanethiol, undecanethiol, dodecanethiol, hexadecanethiol, heptadecanethiol, octadecanethiol, nonadecanethiol, eicosanethiol, most preferably heptadecanethiol, octadecanethiol, nonadecanethiol, eicosanethiol. In one preferred embodiment alkanethiol is octadecanethiol. 
     In a preferred embodiment, the water-based composition is free of chromate and/or free of organic solvent. 
     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. 
     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-emulsifier: 0.1-5 g/L, preferably 0.5-2 g/L
 
     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. 
     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.
 
     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. 
     Contacting in step b. may be done additionally under electroless conditions, i.e. without supplying a current between the metal surface and an electrode. 
     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. 
     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 
     Hereinafter, the invention is illustrated by working examples. 
     Inventive Example 1 
     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. 
     The water-based composition was made by dissolving the following components in water:
         a. alkanethiol: octadecanethiol. (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-emulsifier: Alcohol C16-18 polyalkylene glycol ether, (CAS Nr. 68002-96-0) amount: 2,5 g/L.       

     Inventive Example 2 
     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: octadecanethiol. (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-emulsifier: Alcohol C16-18 polyalkylene glycol ether, (CAS Nr. 68002-96-0) amount: 2.5 g/L.       

     Comparative Example 
     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 
     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. (cyanide-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/dm 2  and V is volt/voltage.
   
               
               

     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. 
     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). 
     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   
               
               

     The observations have been carried out without any instruments by skilled person.
         Sulphide test
           Material: Glass beaker   Chemicals: Potassium Sulphide 44% K 2 S, 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 
     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 
     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) 
     Water-based composition conditions: pH 2.5—Temperature 55° C.—agitation 200 RPM—immersion process for 1 min, rinse &amp; dry. 
     
       
         
           
               
             
               
                   
               
               
                 Test material: bright decorative silver layer (Silverlume ® Plus) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Compound of 
                 0 g/L 
                 2 g/L 
                 3 g/L 
                 4 g/L 
               
               
                 formula I 
                 (comparative 
                 (c1-c3) 
                 (c1) 
                 (c1) 
               
               
                   
                 example) 
               
               
                 Residues 
                 Very poor 
                 Excellent 
                 Excellent 
                 Excellent 
               
               
                   
                 (many 
                 (none) 
                 (none) 
                 (none) 
               
               
                   
                 residues) 
               
               
                 Anti-tarnish 
                 Very poor 
                 Improved 
                 Strongly 
                 Excellent 
               
               
                 (after 5 min into 
                 (dark 
                 (yellow 
                 improved 
                 (no discoloration) 
               
               
                 K 2 S 2%) 
                 discoloration) 
                 discoloration) 
                 (Yellow to no 
               
               
                   
                   
                   
                 discoloration) 
               
               
                   
               
            
           
         
       
     
     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 &amp; dry. 
     
       
         
           
               
             
               
                   
               
               
                 Test material: bright silver cyanide free (Argalux NC ™ mod.) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Compound (c1) 
                 0 g/L 
                 3 g/L 
                 4 g/L 
               
               
                 of formula I 
                 (comparative 
               
               
                   
                 example) 
               
               
                 Residues 
                 Poor (many) 
                 Excellent (none) 
                 Excellent (none) 
               
               
                 Anti-tarnish 
                 Very poor 
                 Strongly improved 
                 Excellent (no 
               
               
                 (after 5 min 
                 (dark colored) 
                 (yellow colored) 
                 discoloration) 
               
               
                 into K 2 S 2%) 
               
               
                   
               
            
           
         
       
     
     Test material: technical silver plated surface (AgO-56™) 
     Water-based composition conditions: pH 2.5—Temperature 55° C.—agitation 200 RPM—immersion process for 1 min, rinse &amp; dry. 
     
       
         
           
               
             
               
                   
               
               
                 Test material: technical silver (AgO-56 ™) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Compound (c1) 
                 0 g/L 
                 3 g/L 
                 4 g/L 
               
               
                 of formula I 
                 (comparative 
               
               
                   
                 example) 
               
               
                 Residues 
                 Poor (many) 
                 Excellent (none) 
                 Excellent (none) 
               
               
                 Anti-tarnish 
                 Very poor 
                 Strongly improved 
                 Excellent (no 
               
               
                 (after 5 min 
                 (dark colored) 
                 (yellow to no 
                 discoloration) 
               
               
                 into K 2 S 2%) 
                   
                 discoloration) 
               
               
                   
               
            
           
         
       
     
     2.3 Cathodic Use 
     Test material: technical silver plated surface (AgO-56™) 
     Water-based composition conditions: pH 2.5—Temperature 55° C.—Agitation 200 RPM—immersion for 1 min or cathodic 0.5 A/dm 2  for 1 min, rinse &amp; dry 
     
       
         
           
               
             
               
                   
               
               
                 Test material: technical silver (AgO-56 ™) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Compound 
                 0 g/L 
                 3 g/L 
               
               
                 (c1) of 
                 (comparative example) 
               
               
                 formula I 
               
            
           
           
               
               
               
               
               
            
               
                 Process 
                 Immersion 
                 Cathodic 
                 Immersion 
                 Cathodic 
               
               
                 Residues 
                 Poor (many) 
                 Poor (many) 
                 Excellent (none) 
                 Excellent (none) 
               
               
                 Anti-tarnish 
                 5 min 
                 10 min 
                 5 min 
                 10 min 
               
               
                 (dipping time 
                 Very poor 
                 Strongly 
                 Good (yellow to no 
                 Excellent (no 
               
               
                 into K 2 S 2%) 
                 (dark colored) 
                 improved 
                 discoloration) 
                 discoloration) 
               
               
                   
               
            
           
         
       
     
     3. Conclusions 
     
         
         
           
             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.