Method for silver plating

Abstract

The aim of the present invention is to provide a method for silver plating that does not comprise the step of forming the nickel-underlayer and that can form a silver-plated layer having sufficient adherence directly on the difficult-to-plate substrates with the use of a halide-free plating bath under a good working environment. The present invention provides a silver plating method onto a substrate on which an oxide layer inhibiting adherence of a plated layer is prone to form, comprising at least the following steps of; (A) degreasing the substrate, (B) removing the oxide layer with a strongly acidic solution from the substrate, and (C) silver plating onto the substrate, without a step of nickel or nickel alloy strike plating in advance, utilizing a phosphines-containing acidic silver plating bath which essentially does not contain halide ion or cyanide ion.

1 . A silver plating method onto a substrate on which an oxide layer that inhibits adherence of a plated layer is prone to form, comprising at least;
 (A) degreasing the substrate,   (B) removing the oxide layer with a strongly acidic solution from the substrate, and   (C) silver plating onto the substrate, without a step of nickel or nickel alloy strike plating in advance, utilizing a phosphines-containing acidic silver plating bath which essentially does not contain halide ion or cyanide ion.   
   
   
       2 . The silver plating method according to  claim 1 , wherein the method further comprises (D) silver plating onto the substrate utilizing a sulfonic acid-containing acidic silver plating bath preceded by step (C). 
   
   
       3 . The silver plating method according to  claim 1 , wherein the phosphines-containing acidic silver plating bath in (C) further contains sulfonate ion. 
   
   
       4 . The silver plating method according to  claim 2 , wherein the silver plating baths in (C) and (D) both have a pH value of less than or equal to 3. 
   
   
       5 . The silver plating method according to  claim 1 , wherein the silver plating bath in (C) contains one or more of the phosphines represented by the general formula (1): 
     
       
         
         
             
             
         
       
     
     wherein X 1 , X 2  and X3, which may be the same or different, each representing a hydrogen atom, a substituted or unsubstituted C1˜C10 alkyl group, or a substituted or unsubstituted benzene ring, the substituents for the substituted alkyl group or the substituted benzene ring being one or more selected from the group consisting of a hydroxyl group, a carboxyl group, a sulfonic group and an amino group, provided that not all of X 1 , X 2  and X 3  being hydrogen atoms simultaneously. 
   
   
       6 . The silver plating method according to  claim 5  wherein the phosphines are lower alkylphosphine represented by the general formula (2): 
     
       
         
         
             
             
         
       
     
     wherein Y 1 , Y 2  and Y 3 , which may be the same or different, each representing an unsubstituted C1˜C3 alkyl group or a C1˜C3 alkyl group substituted with one or more substituents selected from the group consisting of a hydroxyl group, a carboxyl group, a sulfonic group and an amino group. 
   
   
       7 . The silver plating method according to  claim 1 , wherein the strongly acidic solution in (B) contains more than or equal to 10 wt % of acid. 
   
   
       8 . The silver plating method according to  claim 1 , wherein the strongly acidic solution in step (B) has a pH value of less than or equal to 2. 
   
   
       9 . The silver plating method according to  claim 1 , wherein the strongly acidic solution in (B) essentially does not contain halide ion. 
   
   
       10 . The silver plating method according to  claim 1 , wherein the strongly acidic solution in (B) contains sulfonic acid. 
   
   
       11 . The silver plating method according to  claim 1 , wherein the above mentioned substrate is made of magnesium, aluminum, titanium, chromium, nickel cobalt, zinc and tin, or an alloy which at least contains one or more metals selected from the group consisting of these metals. 
   
   
       12 . The silver plating method according to  claim 11 , wherein the substrate is made of a chromium-containing alloy. 
   
   
       13 . The silver plating method according to  claim 12 , wherein the substrate is made of a stainless steel. 
   
   
       14 . The silver plating method according to  claim 13 , wherein the substrate is made of an austenitic stainless steel. 
   
   
       15 . The silver plating method according to  claim 11 , wherein the substrate is made of titanium. 
   
   
       16 . The silver plating method according to  claim 11 , wherein the substrate is made of tin or tin-alloy. 
   
   
       17 . The silver plating method according to  claim 11 , wherein the above mentioned substrate is an alloy of tin and at least one or more metals selected from copper, zinc, silver, indium, gold, lead and bismuth. 
   
   
       18 . The silver plating method according to  claim 1  wherein an insoluble anode is used in at least one of (C) and (D). 
   
   
       19 . The silver plating method according to  claim 18  wherein the insoluble anode is selected from the group consisting of a carbon anode, a platinum anode, a platinum-coated titanium anode, an oxidized ruthenium-coated anode and an oxidized iridium-coated anode. 
   
   
       20 . The silver plating method according to  claim 18  wherein the uppermost layer of the above mentioned insoluble anode comprises an uppermost layer made of one or more material(s) selected from the group consisting of spinel, garnet, glass, and perovskite. 
   
   
       21 . The silver plating method according to  claim 2  wherein an insoluble anode is used in at least one of (C) and (D). 
   
   
       22 . The silver plating method according to  claim 21  wherein the insoluble anode is selected from the group consisting of a carbon anode, a platinum anode, a platinum-coated titanium anode, an oxidized ruthenium-coated anode and an oxidized iridium-coated anode. 
   
   
       23 . The silver plating method according to  claim 21  wherein the uppermost layer of the above mentioned insoluble anode comprises an uppermost layer made of one or more material(s) selected from the group consisting of spinel, garnet, glass, and perovskite.