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
  • C23C18/31—Coating with metals
  • C23C18/32—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron
  • C23C18/34—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents
  • C23C18/36—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents using hypophosphites
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/922—Static electricity metal bleed-off metallic stock
  • Y10S428/9335—Product by special process
  • Y10S428/936—Chemical deposition, e.g. electroless plating
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12736—Al-base component
  • Y10T428/1275—Next to Group VIII or IB metal-base component
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12771—Transition metal-base component
  • Y10T428/12861—Group VIII or IB metal-base component
  • Y10T428/12944—Ni-base component

Definitions

• the subject matter of this invention is an electroless nickel plating solution especially formulated for nickel plating aluminum alloys.
• Aluminum is a difiicult metal to plate from an electroless bath because aluminum is active and deposition over aluminum takes place at a rapid rate.
• there is excessive gassing at the aluminum interface resulting in migration of smut particles from the aluminum surface into the plating bath.
• These particles act as nuclei for deposition of nickel resulting in spontaneous decomposition (triggering) of the bath and loss thereof, as well as plate-out on walls of the plating tank, racks and the like.
• the invention overcomes these difficulties by addition of an unsaturated carboxylic acid to the solution alone or preferably in combination with a second stabilizer.
• the acid acts to suppress the rate of deposition over aluminum decreasing gas evolution and migration of smut into the solution. As a result, triggering of the solution is retarded.
• This invention relates to a metal-depositing composition and more particularly, to an electroless nickel plating solution especially formulated for nickel plating aluminum which composition is characterized by the addition of an unsaturated carboxylic acid suppressant preferably in combination with a stabilizer for said electroless nickel composition.
• Known electroless nickel deposition solutions generally comprise at least four ingredients dissolved in a solvent, typically water. They are (l) a source of nickel ions, (2) a reducing agent such as hypophosphite, (3) an acid or hydroxide pH adjustor to provide required pH, and (4) a complexing agent for the nickel ions suflicient to prevent precipitation in solution.
• a solvent typically water.
• smut is removed prior to plating by contact with a solution of a desmuter such as an aqueous nitric acid solution. Regardless of the nature of the plating operation, some smut is usually retained on the surface of the aluminum substrate to be plated, though the amount may vary.
• a desmuter such as an aqueous nitric acid solution.
• the present invention is predicated in part upon the discovery that the addition of an unsaturated carboxylic acid to substantially any electroless nickel hypophosphite plating solution results in suppression of the plating rate and descreased gassing. Consequently, introduction of smut particles into the electroless plating solution as a consequence of excessive gassing is minimized and the useful life of the solution is prolonged.
• the unsaturated carboxylic acid might also coordinate with aluminum introduced into the solution both from the smut and from free aluminum ions migrating into solution as a result. of initial displacement plating of nickel for aluminum. Since aluminum ions in solution might accelerate triggering, coordination of the ions could also act to increase the useful life of the solution.
• the unsaturated carboxylic acid improves the effectiveness of prior art stabilizers, whether the solutions are used to plate aluminum or other materials.
• the deposits seem to have unique properties. For example, at substantially any deposit thickness, the deposit has a bright, shiny surface appearance.
• deposits from prior art nickel solutions can be made to have a bright, shiny appearance in relatively thick sections, i.e., /2 mil or more, but generally have a matted appearance when thin.
• prior art electroless nickel over aluminum when rinsed with water, frequently stains. The electroless nickel of this invention over aluminum does not stain when rinsed.
• the electroless nickel solutions of this invention are especially useful for plating aluminum due to the unsaturated carboxylic acid alone and preferably in combination with a stabilizer.
• the unsaturated carboxylic acid contemplated is that soluble in solution and containing one or more double or triple bonds.
• low molecular weight aliphatic monoand polycarboxylic acids i.e. having from 2 to 6 carbon atoms in the chain are more soluble than aromatic and higher molecular weight aliphatic carboxylic acids and are therefore preferred.
• carboxylic acids examples include acrylic acid, maleic acid, propiolic acid, acetylene dicarboxylic acid, Lacic acid, vinyl acetic acid, tetraloic acid, glutaconic acid, itaconic acid, mesaconi acid, allyl acetic acid, ethylacrylic acid, vinyl acrylic acid, muconic acid, tiglic acid, sorbic acid and fumaric acid.
• carboxylic acids can be substituted with various substituents such as alkyl groups, hydroxyl groups, nitro groups, amino groups, halo groups, sulfonic acid groups and the like.
• substituted unsaturated carboxylic acids include by way of examples, bromocrotonic acid, bromomaleic acid, chloroacrylic acid, chloromaleic acid, dibromomaleic acid, dimethylacrylic acid, ethylcrotonic acid, nitro glutaconic acid, methylfumaric acid, mucobromic acid, mucochloric acid, and teraconic acid. Acids of this nature constitute a lesser prefered embodiment of this invention, though are still considered suitable for purposes set forth herein.
• unsaturated carboxylic acids that are insoluble or partially soluble in the electroless nickel solution may be made more soluble by substitution onto the compound of a solubilizing group such as a halo group, nitro group, sulfo group, hydroxyl group, amino group and the like.
• a solubilizing group such as a halo group, nitro group, sulfo group, hydroxyl group, amino group and the like.
• aromatic carboxylic acids that might otherwise be unsuitable or provide limited improvement may be made soluble and thus fulfill the objects of this invention.
• Typical examples of such materials include bromo cinnamic acid, coumaric acid, dihydroxycinnamic acid, nitrocinnamic acid, phenyl angelic acid, and the like.
• the aromatic unsaturated carboxylic acids are least preferred.
• the amount of carboxylic acid added to solution is not critical, small amounts providing some benefit and larger amounts providing greater benefit until a practical maximum is reached.
• the amount of unsaturated carboxylic acid is that amount that at least doubles the life of the electroless nickel solution in contact with the aluminum part to be plated. More specifically, it is preferred that the carboxylic acid range from about 0.001 mole per liter of solution to saturation and most preferably, from about 0.01 to 0.20 mole per liter of solution.
• the principal function of the unsaturated carboxylic acid in solution is to prevent triggering of the electroless nickel solution in contact with an aluminum substrate. It is believed that triggering is caused by smut and possibly, aluminum ions entering the solution by virtue of excessive gassing during plating with respect to the smut and by displacement plating of nickel for aluminum with respect to the aluminum ions at least during the initial phase of plating.
• the unsaturated carboxylic acid appears to suppress gas formation on the surface of the aluminum during plating thus preventing much of the smut from breaking off the surface and entering the solution. Since the unsaturated carboxylic acid suppresses gas evolution, it will be referred to at times throughout the remainder of this specification as a suppressant. It is also conceivable that triggering is prevented by the unsaturated carboxylic acid coordinating with the aluminum and further by dissolving at least in part, any smut that does enter the solution.
• the unsaturated carboxylic acid is used in conjunction with an electroless nickel solution stabilizer because the combination provides baths of substantially enhanced stability when used to plate aluminum.
• the combination provides, in many cases, a synergistic improvement.
• Illustrative of stabilizers used for electroless nickel solutions are the divalent sulphur containing compounds many of which are disclosed in U.S. Pat. No. 3,361,540 incorporated herein by reference.
• Representative examples of such sulphur compounds are the inorganic sulfides such as potassium sulfide, sodium sulfide, sodium polysulfide, and potassium polysulfide; organic and inorganic thiocompounds such as sodium thiocyanate, potassium thiocyanate, potassium dithionate, sodium thiosulfate, and potassium thiosulfate; and organic sulphur containing compounds such as thiourea, Z-mercaptobenzothiazole, 1,2- ethanedithiol, 1,2-benziosothioazine, methionine, 2,2-thiodiethanol, dithioglycol and thioglycolic acid.
• iodate compounds such as potassium and sodium iodate
• sources of Pb++ such as lead acetate
• sources of mercury ions such as mercuric acetate.
• each of R, R' and R" are selected from the class of lower monovalent hydroxyalkyl, cyclohydroxyalkyl, and hydroxyalkyl ether.
• examples include ethyonyl cyclobexanol, methyl butynol, methyl pentynol, dimethyl hexnol, Z-butyne-l, 4-diol, dimethyl hexynediol, propargyl alcohol, hexnol and ethyl actynol.
• the stabilizers will be referred to as solution soluble acetylenic compounds. Further examples of such compounds are set forth in US Pat. No. 3,457,089.
• the electroless nickel solution in accordance with the invention will comprise a source of nickel ions, a reducing agent for the nickel ions such as a hypophosphite, a complexing agent to maintain the nickel ions in solution and a stabilizer for the solution.
• a source of nickel ions such as a hypophosphite
• a complexing agent to maintain the nickel ions in solution such as a hypophosphite
• a stabilizer for the solution a stabilizer for the solution.
• suitable sources of nickel ions, complexing agents, stabilizers, and the like as well as the relative amounts of each are well known in the art and illustrated in the above referenced patents.
• One such advantage is that the electroless nickel deposits from the solutions of this invention are bright regardless of thickness whereas prior art deposits may be bright in relatively thick sections, but in thin deposits, typically are matted.
• a further advantage is that the deposits of the invention over aluminum do not stain when rinsed in water whereas deposits from prior art solutions are prone to staining.
• the electroless plating solutions of the invention may be used to deposit nickel over substantially any substrate in the same manner as any prior art electroless nickel solution.
• the surface of the part to be plated should be free of grease and contaminating material.
• the surface area to receive the deposit must be sensitized to render it catalytic to the reception of the electroless nickel as by the Well known treatment with an acidic aqueous solution of stannous chloride followed by treatment with a dilute aqueous solution of palladium chloride.
• the aluminum When using the electroless nickel solutions of this invention to plate aluminum, the aluminum must be presodium hypophosphite and water to 1 liter of solution. In some of the examples, for purposes of illustration, no maleic acid is used. In others, maleic acid alone is used. In still other examples, maleic acid is used in combinapared by removing the oxide film. In this respect, the 5 tron with prior art stabihzers. Where maleic ac1d is used, aluminum is first preferably degreased such as by conit 18 added 1n an amount of 2 /2 grams per liter of solution. tact with an organic solvent.
• the entry in the column indicates the number of actual plating minutes prior to triggeri aluminum part may be contacted with a desmutter such as a mixture of nitric acid and hydrofluoric acid.
• the aluminum alloy used was a number 6061 alloy which was cut to a size measuring 2 /2 x 3 inches.
• parts were prepared by etching in a hydrochloric acid solution maintained at 70 F. for a period of four minutes. This provides an even gray-black coating over the aluminum. The parts were then rinsed for two minutes with water in an overflow rinse tank with water temperature at 60 F.
• a first part was plated in an electroless nickel solution for 15 minutes, removed and saved. If the solution did not trigger during this period, the procedure was repeated by plating a second part for a period of 15 minutes in the same solution. This procedure was continuously repeated until the solution triggered. The total number of parts plated and the total effective plating time of the solution were recorded. All electroless nickel solutions were used at a temperature between 195 and 200 F. unless otherwise indicated.
• the maleic acid alone provides some benefit, but major benefit is realized when the maleic acid is used in conjunction with a prior art stabilizer. It can also be seen from the table that the maleic acid alone and in combination with the prior art stabilizer provdes effective results regardless of the complexing agent used in the solution.
• Cinnamic acid was added to the above formulation in amounts varying from no addition to 7 /2 grams per liter to show the effect of concentration on a suppressant activity.
• the amounts used and the results are set forth in the following table:
• the carboxylic acid suppressant was used in an amount less than the amount of complexing agent since it does not function by itself as the complexing agent for the solution.
• an aqueous electroless nickel plating solution comprising a source of nickel ions in an amount sufiiicient to provide a useful deposit, hypophosphite as a reducing agent for said nickel ions and complexing agent to maintain said nickel ions in solution, the improvement comprising the addition to the solution of at least 0.001 mole per liter of solution of a solution soluble aliphatic, unsaturated carboxylic acid as a suppressant, said carboxylic acid is selected from the group of acrylic acid, maleic acid, propiolic acid, acetylene dicarboxylic acid, crotonic acid, vinyl acetic acid, tetraloic acid, glutaconic acid, taconic acid, mesaconic acid, alkyl acetic acid, ethylacrylic acid, vinyl acrylic acid, muconic acid, sorbic acid, fumaric acid and cinnamic acid and being present in an amount less than the amount of complexing agent.
• the nickel plating solution of claim 4 where the stabilizer is selected from the group consisting of divalent sulphur compounds, lead ions, iodate compounds and solution soluble acetylinic compounds.
• R, R and R" are radicals selected from the group of monovalent hydroxyalkyl, cyclohydroxyalkyl and bydroxyalkyl ether.
• the nickel plating solution of claim 4 where the stabilizer comprises a maximum of parts per million parts of solution.
• an aqueous electroless plating solution for plating over aluminum comprising a source of nickel ions in an amount sufficient to provide a useful deposit, hypophosphite as a reducing agent for said nickel ions, a complexing agent to maintain said nickel ions in solution and a stabilizing agent for said solution, the improvement comprising the addition to the solution of at least 0.001 mole of an aluminum complexing agent that is an unsat urated aliphatic carboxylic acid in an amount sufficient to suppress evolution of gas from said aluminum surface, said carboxylic acid is selected from the group of acrylic acid, maleic acid, propiolic acid, acetylene dicarboxylic acid, crotonic acid, vinyl acetic acid, tetraloic acid, glutaconic acid, taconic acid, mesaconic acid, alkyl acetic acid, ethylacrylic acid, vinyl acrylic acid, muconic acid, sorbic acid, fumaric acid and cinnamic acid and being present in an amount less than
• the nickel plating solution of claim 12 where the stabilizer is selected from the group consisting of divalent sulphur compounds, lead ions, iodate compounds and solution soluble acetylinic compounds.
• a method for electroless nickel plating of aluminum comprising contact of an aluminum part with the electroless nickel plating solution of claim 1.
• a method for electroless nickel plating of aluminum comprising contact of an aluminum part with the electroless nickel plating solution of claim 12.

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• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemically Coating (AREA)

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Cited By (18)

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• 1971
  • 1971-07-06 US US00160087A patent/US3782978A/en not_active Expired - Lifetime
• 1972
  • 1972-05-31 IT IT25185/72A patent/IT956096B/it active
  • 1972-06-21 JP JP6145672A patent/JPS533326B1/ja active Pending
  • 1972-07-05 FR FR7224271A patent/FR2144782B1/fr not_active Expired
  • 1972-07-06 GB GB3170672A patent/GB1344760A/en not_active Expired

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