Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/58—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of copper
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/38—Electroplating: Baths therefor from solutions of copper

Definitions

• the present invention relates to a copper-zinc alloy electroplating bath and a plating method using it; more particularly, a cyanide-free copper-zinc alloy electroplating bath which can form a glossy and uniform alloy layer even at a higher current density, and a plating method using it.
• copper-zinc alloy plating is industrially widely used as decorative plating to give a brass-colored metallic luster and tone to metal products, plastic products, ceramic products and the like.
• a conventional plating bath contains a large amount of cyanide, its toxicity has become a big problem, and the burden of disposal of cyanide-containing waste has been large.
• sequential plating is a practical method for application of brass plating to a product to be plated, and in such a method, a copper-plated layer and a zinc-plated layer are sequentially plated on the surface of the product to be plated by electrodeposition, followed by a thermal diffusion step.
• a pyrophosphate copper plating solution and an acidic zinc sulfate plating solution are usually used (e.g., Patent Document 1).
• Patent Document 2 As a method for simultaneous plating with copper-zinc, a cyanide-free copper-zinc plating bath has also been reported, and a plating bath using a glucoheptonate bath or a potassium pyrophosphate bath supplemented with histidine as a complexing agent has been proposed (e.g., Patent Document 2).
• the present invention aims to provide a cyanide-free copper-zinc alloy electroplating bath which is capable of forming a glossy and uniform alloy layer having the desired composition even at a higher current density than that for a conventional electroplating bath with high productivity, and a plating method using it.
• a glossy and uniform alloy layer can be obtained by adjusting pH of the copper-zinc alloy electroplating bath at a current density ranging from a low current density to a high current density, thereby completing the present invention.
• the copper-zinc alloy electroplating bath of the present invention comprises at least one selected from a copper salt, zinc salt, alkali metal pyrophosphate, and amino acid or a salt thereof; and has a pH of 8.5 to 14.
• pH is preferably 10.5 to 11.8; and the concentration of the amino acid or a salt thereof is preferably 0.08 mol/L to 0.22 mol/L; and the concentration of the amino acid or a salt thereof is more preferably 0.1 mol/L to 0.13 mol/L.
• the total concentration of copper and zinc contained in the copper-zinc alloy electroplating bath is preferably 0.03 to 0.3 mol/L; at least one selected from alkali metal hydroxides and alkaline earth metal hydroxides is preferably contained; and the amino acid or a salt thereof is preferably histidine or a salt thereof.
• the method of copper-zinc alloy electroplating of the present invention comprises using the copper-zinc alloy electroplating bath, wherein the cathode current density is higher than 5 A/dm 2 and not higher than 10 A/dm 2 .
• a cyanide-free copper-zinc alloy electroplating bath which is capable of forming at a current density ranging from a low current density to a high current density a uniform and glossy alloy layer having the desired composition and is capable of utilizing a higher current density than that for a conventional electroplating bath can be realized, thereby enhancing the productivity.
• the copper-zinc alloy electroplating bath of the present invention comprises at least one selected from a copper salt, zinc salt, alkali metal pyrophosphate, and amino acid or a salt thereof; and has a pH adjusted within the range of 8.5 to 14.
• any one can be employed as long as it is known as a copper ion source for plating baths, and examples thereof include copper pyrophosphate, copper sulfate, cupric chloride, copper sulfamate, cupric acetate, basic copper carbonate, cupric bromide, copper formate, copper hydroxide, cupric oxide, copper phosphate, copper silicofluoride, copper stearate and cupric citrate, and either only one of these or two or more of these may be used.
• any one can be employed as long as it is known as a zinc ion source for plating baths, and examples thereof include zinc pyrophosphate, zinc sulfate, zinc chloride, zinc sulfamate, zinc oxide, zinc acetate, zinc bromide, basic zinc carbonate, zinc oxalate, zinc phosphate, zinc silicofluoride, zinc stearate and zinc lactate, and either only one of these or two or more of these may be used.
• the total concentration of copper and zinc dissolved in the plating bath is preferably within the range of 0.03 to 0.30 mol/L.
• concentration is lower than 0.03 mol/L, deposition of copper is predominant and hence a good alloy layer can hardly be obtained.
• concentration is higher than 0.30 mol/L, gloss cannot be obtained on the surface of the plated coating.
• alkali metal pyrophosphate any one can be employed as long as it is known, and examples thereof include sodium salt and potassium salt thereof.
• the copper-zinc alloy electroplating bath of the present invention It is important for the copper-zinc alloy electroplating bath of the present invention to have a pH within the range of 8.5 to 14, preferably 10.5 to 11.8. When the pH is lower than 8.5, a glossy and uniform alloy layer cannot be obtained, while when the pH is higher than 14, the current efficiency decreases. Adjustment of pH of the copper-zinc alloy electroplating bath of the present invention can be preferably carried out with an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide; or an alkaline earth metal hydroxide such as calcium hydroxide; preferably potassium hydroxide.
• an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide
• an alkaline earth metal hydroxide such as calcium hydroxide
• the concentration of the amino acid or a salt thereof of the copper-zinc alloy electroplating bath of the present invention is within the range of 0.08 mol/L to 0.22 mol/L, preferably 0.1 mol/L to 0.13 mol/L.
• concentration of the amino acid or a salt thereof is lower than 0.08 mol/L, a uniform alloy layer cannot be obtained at a high current density, while when the concentration of the amino acid or a salt thereof is higher than 0.22 mol/L, copper predominates in the composition of the alloy layer, so that a uniform alloy layer having the desired composition cannot be obtained.
• amino acid any one can be employed as long as it is known, and examples thereof include ⁇ -amino acids such as glycine, alanine, glutamic acid, aspartic acid, threonine, serine, proline, tryptophan and histidine, and hydrochlorides and sodium salts thereof. Histidine is preferred. Either only one of these or two or more of these may be used.
• the amount of each of the above-described components to be added in the present invention is not limited and may be selected appropriately.
• the amount of the copper salt is preferably about 2 to 40 g/L in terms of copper;
• the amount of the zinc salt is preferably about 0.5 to 30 g/L in terms of zinc;
• the amount of the alkali metal pyrophosphate is preferably about 150 to 400 g/L;
• the amount of the amino acid or a salt thereof is preferably about 0.2 to 50 g/L.
• the copper-zinc alloy electroplating bath of the present invention is employed, and plating is carried out at a high current density higher than 5 A/dm 2 and not higher than 10 A/dm 2 .
• a conventional electroplating method may be employed.
• the electroplating may be carried out at a bath temperature of about 30 to 40°C without stirring, with mechanical stirring or with air agitation.
• any one may be used as long as it is one used for conventional electroplating of a copper-zinc alloy.
• the copper-zinc alloy electroplating bath of the present invention it is possible to carry out plating at a high current density higher than 5 A/dm 2 and not higher than 10 A/dm 2 , so that a glossy and uniform copper-zinc alloy layer can be formed with higher productivity than before.
• the material to be plated may be subjected to conventional pretreatment such as buffing, degreasing, and soaking in a dilute acid according to conventional methods, and an undercoat such as gloss nickel plating may be also applied to the material.
• a conventional operation such as washing with water, washing with hot water or drying may be carried out, and soaking in a dichromic acid dilute solution, clear painting or the like may be further carried out as required.
• the material to be plated is not limited, and any one to which a copper-zinc alloy electroplating coat can be usually applied may be used, and examples thereof include metal products such as steel filaments used in steel cords for reinforcing rubber articles; plastic products; and ceramic products.
• the copper-zinc alloy electroplating bath of each Example was prepared, and according to the plating conditions in Tables 1 to 3, copper-zinc alloy electroplating was carried out. After preparation of each plating bath, plating was immediately carried out, and the deposited amount of plating and the alloy composition were analyzed. The roughness of the alloy surface was observed by a laser microscope to obtain the roughness parameters Ra, Rv and Rz. Further, the range of current density within which a glossy and uniform alloy layer can be obtained was calculated. Tables 1 to 3 below also show the obtained results.
• Ra the centerline average roughness
• a portion of the roughness profile, which portion had a measurement length L in the direction of its centerline, was sampled, and the centerline of the sampled portion was taken along the x-axis and the longitudinal magnification was taken along the y-axis to represent the roughness profile as y f(x).
• the value Ra given by the above equation was represented in micrometers ( ⁇ m).

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• 2008
  • 2008-11-26 WO PCT/JP2008/071470 patent/WO2009069669A1/fr active Application Filing
  • 2008-11-26 EP EP08854020A patent/EP2218804A4/fr not_active Withdrawn
  • 2008-11-26 US US12/744,641 patent/US20100243466A1/en not_active Abandoned
  • 2008-11-26 CN CN2008801177603A patent/CN101874128B/zh not_active Expired - Fee Related

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