Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/18—Pretreatment of the material to be coated
  • C23C18/20—Pretreatment of the material to be coated of organic surfaces, e.g. resins
  • C23C18/28—Sensitising or activating
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/1601—Process or apparatus
  • C23C18/1617—Purification and regeneration of coating baths
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/18—Pretreatment of the material to be coated
  • C23C18/20—Pretreatment of the material to be coated of organic surfaces, e.g. resins
  • C23C18/22—Roughening, e.g. by etching
  • C23C18/26—Roughening, e.g. by etching using organic liquids

Definitions

• This invention is concerned with metal plating of polymeric resin substrates, and is more particularly directed to improvements in that portion of the metallizing process involving the laying down of an initial deposit or film of a desired metal, which deposit is continuous in its coverage of the substrate and is firmly bonded thereto.
• the art of metallizing plastics both for decorative and functional applications is undergoing rapid development.
• the general method employed consists of first chemically depositing on a polymeric plastic substrate a preliminary conductive metallic coating after which the substrate can then be electroplated by standard electrochemical techniques.
• the successful application of the initial conductive metallic layer is of crucial importance to the subsequent successful electroplating of one or more layers of the same or different metal in building up a total metallic deposit of desired thickness and finish characteristics.
• Copper, nickel, chromium and sometimes cobalt are the metals most commonly applied to commercial articles, and the process is used extensively in the automotive, appliance, plumbing and related industries today.
• plating skip or lack of continuity in the coverage of the substrate by the deposited metal. This is commonly noted on areas of the plastic which are highly stressed due to the method of molding the particular part. Plating skips often occur in other nonstressed areas also. Poor adhesion is another important problem, and often this does not show up until a late stage in the process, usually not until after completion of the metallizing procedure. All of this adds to the expense because the part must then be scrapped. Quite frequently these deficiencies arise from completely unrecognized conditions which further complicate the process.
• hexavalent chromium which is present in the usual etching step preceding activation, is a potent deterrent or poison to good deposition of the desired metal coating on the substrate. It is common practice, accordingly, to incorporate after the etching step and prior to the chemical plating operation one or more thorough water rinses or other treatment solutions containing chrome-reducing agents to kill residual hexavalent chromium ions that may be present on the substrate. Obviously such preactivation chrome-kill treatments must not also act to impede the activation of the substrate surface. There is always too a problem of simple mechanical trapping of trace amounts of hexavalent chromium in crevices or other inaccessible areas where the substrate article has a complex shape or configuration.
• Accelerating a substrate surface after its activation is of course a generally well'known procedure.
• the use of this step is postulated on the assumption that during activation of the substrate not only is palladium (or other catalytic metal) laid down to provide the desired initiating foci for the reduction of metal ions in the plating solution, but excess stannous ions and/or other impurities which are also present in all of the commercial activating solutions, are also deposited on or at least adhere to the surface of the substrate.
• These stannous ions and other impurities are deterrents to subsequent deposition of metal, just as are the residual adherent hexavalent chromium ions mentioned above, and must be removed. This removal of impurities is the primary function of the usual accelerating solution.
• the invention is illustrated by the following example.
• a. immerse substrate in aqueous emulsion of an organic preconditioning agent comprising approximately, per liter of solution, 40 mls. of steam-distilled turpentine emulsified in water with surfactants.
• an organic preconditioning agent comprising approximately, per liter of solution, 40 mls. of steam-distilled turpentine emulsified in water with surfactants.
• compositions useful in this step are shown more particularly in copending application Ser. No. 758,589, filed Sept. 9, 1968.
• the resulting nickel deposit is smooth, bright and completely continuous in coverage of the substrate, including such difficulty platable areas as locations corresponding to gating points in the mold, or where the surface configuration of the substrate produces deep crevices or relatively inaccessible pockets.
• Copper plating of the substrate in place of nickel can similarly be effected with equally good result simply by substituting a commercial electroless copper plating solution for the nickel in Step (k) of the foregoing cycle, all other steps being unchanged.
• a typical copper plating solution is disclosed in U.S. Pat. No. 3,095,309. The system is also effective for electroless plating of cobalt, using any of the commercially available electroless cobalt plating solutions.
• EXAMPLE II An accelerating solution identical with that used in Step (i) of example I is purposely contaminated with incremental additions of hexavalent chromium ion in controlled amounts, and identical polypropylene samples are plated in accordance with the previously described procedure at each of the different hexavalent chromium ion concentration levels in the accelerating solution. It is found that the addition of up to a total of 0.5 parts per million p.p.m. to the accelerating solution produces no noticeable effect upon the resulting nickel or copper plate, the deposit still being complete and showing no evidence of skipping. However, upon further addition, at approximately a level of 0.6 p.p.m. (total) hexavalent chromium ion in the accelerating solution, skipping or misplating of the part results.
• EXAMPLE III A test similar to that described in example II was run but in this instance the concentration of the palladium chloride accelerating solution was increased to a level of approximately 0.0261 percent (wt.) palladium chloride. The incremental addition to this accelerating solution of hexavalent chromium ion in 0.5 p.p.m. amounts produced no evidence of skipping after a total of 1.0 p.p.m. of contaminant had been added; but severe skipping did occur when the level reached l.5 p.p.m. hexavalent chromium ion.
• the solution can be readily rejuvenated by the addition of a soluble source of stannous ions to reduce the hexavalent chromium to trivalent condition. This latter ion does not interfere or cause plating skip. This is illustrated by the following.
• the reaction involved in the addition of the stannous ion appears to be reduction of the hexavalent chromium ion to trivalent condition, with simultaneous oxidation of the stannous to the stannic condition.
• the chromium ion poisons the plating operation only when present in the hexavalent form, as it has been found that the presence of trivalent chromium up to at least 650 p.p.m. in the accelerating solution produces no adverse effects on the coverage or adhesion of the plate.
• the manner of adding the stannous ions to the accelerating solution is important in order to avoid simultaneous reduction of palladinous ions to particulate palladium and deterioration of the accelerating solution for that reason.
• a rejuvenating solution containing 0.84 pounds of stannous chloride, 3.96 pounds of concentrated hydrochloric, balance water, per gallon of total solution results in immediate fonnation of substantial particulate palladium in the accelerating solution.
• 0.1 ml. of that solution is effective in countering the adverse effect of 2 p.p.m. of hexavalent chromium ion in 1 liter of accelerating solution, in that complete plating coverage of the substrate article is obtained.
• the operative range of solutions comprises from about 0.05 to 0.3 percent by weight (0.5 to 3.0 g./l) stannous chloride and 0.05N to 0.15N hydrochloric acid.
• the rejuvenating effect of the stannous ion upon the accelerating solution appears to be unique in that other common reducing agents do not overcome the poisoning effect of hexavalent chromium ion.
• the addition of as much as 24 ml. per liter of hydrogen peroxide (30 percent) sill is not effective to overcome the complete inhibition by the contaminant of any metal deposit upon the substrate.
• Hexavalent chromium ion is not the only trace contaminant or impurity in the accelerating solution which will inhibit the satisfactory deposit of a metal plate on the substrate, although it is the principal one usually encountered by reason of the preceding chromic-sulfuric acid etch step in the plating cycle.
• ferric ions in the accelerating solution will also produce serious skipping in the plated deposit. In this case it is generally found that the level at which skipping begins to occur is on the order of 5-6 p.p.m. of ferric ion.
• the inhibiting action of this contaminant can likewise be countered by the addition of stannous ions to the accelerating solution to maintain the ferric ion concentration below the aforesaid level of 56 p.p.m.
• the improvement afforded by the present invention is applicable to substrates other than polypropylene mentioned in the foregoing examples.
• the plating of phenolic, epoxy and polysufone polymers, as well as copolymers, such as acrylonitrile-butadiene-styrene is similarly improved, and it appears that the invention is applicable to any of the usual chemically platable plastics.
• a chemical plating process for depositing a continuous, adherent meta] film on the surface of a polymeric plastic substrate, including the steps of etching the substrate surface in a chromic acid containing bath, activating the substrate surface by immersion in an acid tin-palladium hydrosol, subjecting the activated surface to contact with an accelerating solution to reduce excess stannous ions codeposited with palladium during the activating step and thereafter immersing the surface in a chemical plating solution of the metal to be deposited, the improvement which comprises: employing in said accelerating step an acidic dilute palladium chloride solution, periodically adding to said accelerating solution an aqueous rejuvenating solution consisting essentially of a dilute source of stannous ions in soluble form sufficient to reduce the hexavalent chromium ion contamination carried into said accelerating solution from the etching step to a level not in excess of about 1 p.p.m. hexavalent chromium per 145 p.p.m. palladinous
• polymeric plastic substrate is selected from the group consisting of acrylonitrile-butadiene-styrene, polypropylene, phenolic, epoxy and polysulfone plastics.
• An aqueous accelerating solution for a chemical plating process which consists essentially of from about 0.002 to 0.03 percent by weight palladium chloride, hydrochloric acid to provide a solution pH not over about 1.0, and from about 0.05 to 0.3 percent by weight stannous chloride but always insufficient in amount to effect stochiometric reduction of the palladium chloride, wherein any hexavalent chromium ion is not in excess ofabout p.p.m.

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemically Coating (AREA)
• Electroplating Methods And Accessories (AREA)

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Country Status (8)

Cited By (6)

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Citations (5)

• 1969
  • 1969-04-07 US US814180A patent/US3622370A/en not_active Expired - Lifetime
• 1970
  • 1970-03-13 GB GB02302/70D patent/GB1276034A/en not_active Expired
  • 1970-03-26 NL NL7004348A patent/NL7004348A/xx unknown
  • 1970-04-06 BE BE748540D patent/BE748540A/xx unknown
  • 1970-04-06 DE DE19702016397 patent/DE2016397A1/de active Pending
  • 1970-04-06 JP JP45028672A patent/JPS502860B1/ja active Pending
  • 1970-04-06 FR FR7012415A patent/FR2042997A5/fr not_active Expired
  • 1970-04-06 ES ES378720A patent/ES378720A1/es not_active Expired

Patent Citations (5)

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