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
  • C23C18/18—Pretreatment of the material to be coated
  • C23C18/20—Pretreatment of the material to be coated of organic surfaces, e.g. resins
  • C23C18/2006—Pretreatment of the material to be coated of organic surfaces, e.g. resins by other methods than those of C23C18/22 - C23C18/30
  • C23C18/2026—Pretreatment of the material to be coated of organic surfaces, e.g. resins by other methods than those of C23C18/22 - C23C18/30 by radiant energy
  • C23C18/2033—Heat
• • 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
  • C23C18/2006—Pretreatment of the material to be coated of organic surfaces, e.g. resins by other methods than those of C23C18/22 - C23C18/30
  • C23C18/2046—Pretreatment of the material to be coated of organic surfaces, e.g. resins by other methods than those of C23C18/22 - C23C18/30 by chemical pretreatment
  • C23C18/2073—Multistep pretreatment
  • C23C18/208—Multistep pretreatment with use of metal first
• • 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
  • C23C18/24—Roughening, e.g. by etching using acid aqueous solutions

Definitions

• a novel surface treatment step which includes an improved neutralizer for the conventional chrome-containing chemical etch, is effective in promoting electroless metal coverage and the adhesion between the electroless metal layer and the substrate.
• This invention relates generally to the electroless deposition of metal onto a chemically etchable, nonconductive substrate as a step preceding the electrolytic deposition of metal thereon. More particularly, the invention relates to a method of increasing the coverage and the adhesion between the electroless metal layer and the substrate, which is particularly useful in the processing of difficult to plate substrates, such as aliphatic polyolefins.
• the basic 3) common to practically all known plastic plating processes may be generally stated as follows: (1) preparation of surface by chemical etching or mechanical roughening, (2) catalytic sensitization with noble metal salts, e.g., PdCl (3) electroless metal deposition, e.g., using a nickel-sodium hypophosphite bath, and (4) electrolytic deposition of metal.
• the principal factor affecting the electroless metal coverage and adhesion in this type of process is step (1) above; for, if the surface is not properly prepared, misplate may occur.
• the substrate is normally cleaned in a dilute alkaline solution to remove grease and surface grime picked up during handling of the parts prior to plating.
• the next step involves the use of a strong oxidizing acid etch containing, for example, sulfuric and/or phosphoric acid and chromic acid.
• the chemical etchs which have been found to be most effective in treating a wide variety of thermoplastic substrates all contain chromic acid. While the surface phenomena are not entirely understood, it is believed that the oxidizing effect of the chemical etch forms epoxy or carboxylic acid groups on some of the carbon to carbon linkages, which are more readily activated by the catalyst used as the next step of the process.
• the present invention concerns itself with the recognition that the use of chromic acid in the etch has an undesirable side efl'ect. it is believed that some trivalent chromium in the etch coordinates with the epoxy oxygen or the carboxylic group in various ways.
• the reaction cannot be easily identified, but it is theorized that the ion formed may contain 2 to 3 water ligands, or may be further combined with the sulfate anion in the case of a sulfuric-chromic acid etchant.
• the trivalent chromium in coordinating with the oxygen, apparently prevents the catalyst from activating the surface in a uniform manner.
• the step following the chemical etch is usually a mild acid bath. It is believed that the complex reaction, whereby the trivalent chromium coordinates with additional functional groups, makes it very difficult for the acid type "neutralizer (for neutralizing" chromium compounds) to have much effect at all on certain plastic substrates, such as polypropylene. Accordingly, the thrust of the present invention is directed to the use of a complexing agent which has the ability to remove trivalent chromium from the surface.
• chelating agents such as ethylenediamine, aqueous ammonia and other amine derivatives may also be effective.
• thermoplastic substrate it is a principal object of the invention to provide an improved process for the electroless deposition of metal, such as, for example, nickel or cobalt, onto a thermoplastic substrate.
• metal such as, for example, nickel or cobalt
• Another object of the invention is to provide a novel chrome neutralizer for the chrome-containing chemical etch commonly employed in the surface treatment phase of the plating process.
• Another object of the invention is to reduce the time required for the etch cycle, which, in the case of hard to plate substrates, is presently minutes or more.
• thermoplastic substrate For purposes of this disclosure, reference will be made to a plateable thermoplastic substrate.
• the most successful of such substrates are acrylonitrile-butadienee-styrene (ABS) graft copolymers, polysulfones, and polypropylene.
• ABS acrylonitrile-butadienee-styrene
• Other thermoplastics that also lend themselves to metal plating by the process of this invention are other polyolefins including polyethylene,
• polySAN acrylonitrile and styrene
• ABS-like plastics including acrylate esterbutadiene-styrene graft polymers and interpolymers, blends of nitrile rubber and polySAN, and ABS-type interpolymers and graft polymers in which one or more of the monomers is substituted with halogen or hydrocarbyl groups.
• the process begins with general cleaning of the articles to remove surface dirt, grease, etc., usually in a mild alkaline bath. This step does not have any direct effect on metal adhesion.
• the parts are then immersed into the chemical etch which contains a mixture of sulfuric acid, chromic acid, and sometimes phosphoric acid. The part is then washed in water and immersed in the chrome neutralizer bath.
• the electroless plating phase begins with a catalyst bath followed by an accelerator.
• the electroless deposition process may be of several known types, such as, for example, those described in the specification of U.S. Pat. No. 3,01 1,920 issued to C. R. Shipley, Jr. on Dec. 5, 1961.
• metal deposition takes place in two stages: (1) sensitization of the substrate surface by means of a catalytic metal; and (2) deposition of the primary metal by means of a reducing agent.
• the surface of the substrate after being properly etched by the process described above, is immersed into a bath containing the catalytic metal; and thereafter, the catalyzed substrate is removed to a bath containing the deposition solution which ordinarily contains a salt of nickel, cobalt, copper, silver, gold, chromium or members of the platinum family, and a reducing agent, commonly formaldehyde, a hypophosphite salt, or dimethylamineborane.
• catalyst and deposition metals are known in the art. For example, the following have been reported to be catalytic to the deposition of nickel and cobalt: copper, beryllium, aluminum, carbon, tungsten, tellurium, cobalt, platinum, silver, boron, thallium, vanadium, titanium, nickel, gold, gennanium, silicon, molybdenum, selenium, iron, tin and palladium, with the precious metals gold, palladium and platinum being preferred.
• the same catalysts promote the deposition of copper, lead, platinum, rhodium, ruthenium, osmium, iridium, iron, silver, aluminum, gold, palladium, and magnesium, with gold, platinum and palladium being preferred.
• Cobalt, nickel, and particularly iron have also been used to catalyze the deposition of chromium.
• the article After removal from the electroless plating bath, the article is rinsed to remove residual electroless metal solution, and then electrolytically plated by any conventional method.
• One preferred series of electrolytically applied metals is l copper (to reduce the effect of thermal shock), (2) nickel, and (3) chromium. It should be understood, however, that any electrolytically deposited metal, or combination thereof, may be used in conjunction with the process.
• the present invention is directed primarily to the use of an improved chrome neutralizer which is capable of forming a complex with trivalent chromium.
• an improved chrome neutralizer which is capable of forming a complex with trivalent chromium.
• examples of such compounds would include ammonium hydroxide, ethylenediamine and other polyamines, EDTA and other carboxy-amino poly acids, amino acids such as glycine, hydroxyamines such as mono-, di-, and triethanolamine; hydroxycarboxylic acids, such as glycolic, citric, and tartaric acids; and possibly chelating phosphates such as pyrophosphon'c acid.
• Electroless nickel-an alkaline nickel bath containing hypophosphite salts and conventional complexing and stabilizing compounds (Marbon N-35) at room temperature for 3 to 8 minutes.
• the plated parts After completion of the plating process, the plated parts had adhesion values of 1 l-l 3 pounds per inch strip and complete coverage.
• EXAMPLE 11 The same type of molded ABS articles as those used in example was used in this example. Steps 1, 2, 3, and 4 were the same as in example 1.
• the chrome neutralizer of step 5 was composed as follows:
• step 5 vol% NH OH solution (26 Be) 90 vol% H O
• step 6 the parts were plated according to steps 7 to 12. Complete coverage of parts and adhesion values of 14-15 pounds per inch strip were achieved.
• step 3A Same as step 3 of example 1.
• Additional parts were processed varying the composition of the bath of step 38 from 5-25 wt% H O; from 1-30 wt% CrO from 20-70 wt% H (93%); and from 10-50 wt% H OP (84%) immersion time ranged from 20-25 minutes.
• the plated parts had only 50-60% coverage.
• EXAMPLE V1 The procedure of example V was followed in plating more of the same polypropylene articles except that step 5 operated at 35 F. and 70 F. and used a chrome neutralizer composed as follows:
• specimens had at least 99% coverage and adhesion values of 26.6 pounds per inch strip.
• EXAMPLE Vll The procedure of example VI was followed except that the chrome neutralizer bath of step 5 was varied in composition between 5 vol% and 50 vol% Nl-LOH. Over 99% coverage was achieved in all cases.
• EXAMPLE Vlll Articles of plating grade polypropylene were processed in the manner described in example Vl excepting the normal etch time of 20-25 minutes (step 2) was reduced to 5, l0 and 15 minutes. Respective adhesion values of 16.0, 24.0, and 29.3 pounds per inch strip were obtained and all samples showed 99-100% coverage.
• EXAMPLE 1X A solution of 134 g. of ammonium acetate per liter of water was used as a neutralizer. The bath was maintained at about F. The treatment times ranged from 1 to 3 minutes. Electroless nickel coverage ranged from 85-90%.
• EXAMPLE X Ammonium nitrate in concentrations of 134 g. per liter, 268 g. per liter, and 402 g. per liter were used on three polypropylene samples. Treatment times ranged from 1 to 3 minutes, and electroless nickel coverage was obtained on the average of about 85%.
• EXAMPLE xn Aqueous sodium ammonium phosphate was employed as neutralizer in substantially the same manner as example VI, i.e., 134 g. per liter. Coverage in excess of 99% was obtained.
• EXAMPLE XIII EXAMPLE XIV Ammonium phosphate (monobasic) was employed in substantially the same manner as example VI using 350 g. per liter. Coverage of substantially 100% was obtained.
• EXAMPLE XV Example VI was repeated except that ethylenediamine in aqueous solution was substituted as the chrome neutralizer. Samples were run from immersion times of l, 2, and 3 minutes and coverage was in excess of 99%. Adhesion values for samples subsequently plated were on the order of -12 lbs/inch.
• EXAMPLE XVI Example VI was repeated except that triethanolamine in aqueous solution was substituted as the chrome neutralizer. Samples were run from immersion times of l, 2, and 3 minutes, and coverage was in about 70-85%.
• Example VI was repeated except that hexamethylenetetramine in aqueous solution was substituted as the chrome neutralizer. Samples were run from immersion times of 1, 2, and 3 minutes, and coverage was in excess of 99%.
• EXAMPLE XVIII Example VI was repeated except that mixtures of hexamethylenetetramine and ethylenediamine in aqueous solution were used as the chrome neutralizer in concentrations ranging from 10% ethylenediamine, to hexamethylenetetramine, up to 50% of each component. All samples were diluted with enough water to form 5% solutions. Electroless nickel coverage of all samples was approximately 100%.
• a method of preparing the surface of a thermo plastic substrate prior to electroless deposition of metal thereon comprising the steps of treating said surface with a chemical etchant containing chromic acid, and subsequently complexing any trivalent chromium adhering to the surface by treating said surface with an aqueous composition selected from the group consisting of ammonium acetate, ammonium nitrate, nickel ammonium sulfate, sodium ammonium phosphate, am-
• monium phosphate diabasic ammonium phosphate (monobasic and citric acid.
• composition contains ammonium phosphate (diabasic).
• composition contains ammonium phosphate (monobasic).

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• 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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Cited By (22)

Citations (5)

• 1969
  • 1969-01-22 US US3620804D patent/US3620804A/en not_active Expired - Lifetime
  • 1969-12-24 NL NL6919435A patent/NL6919435A/xx unknown
• 1970
  • 1970-01-09 ES ES375284A patent/ES375284A1/es not_active Expired
  • 1970-01-10 DE DE19702000953 patent/DE2000953A1/de active Pending
  • 1970-01-13 BE BE744385D patent/BE744385A/fr unknown
  • 1970-01-14 FR FR7001266A patent/FR2028856A1/fr not_active Withdrawn

Patent Citations (5)

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