United States Patent 19 11 4,160,049 Narcus 45) Jul. 3, 1979

54 BRIGHT ELECTROLESS PLATING PROCESS PRODUCING TWO-LAYER OTHER PUBLICATIONS NICKEL COATINGS ON DELECTRIC Industrial Finishing, "How to Get Quality Plated Plas SUBSTRATES tic Parts", pp. 36-39, Nov. 1977. Pearlstein, Modern Electroplating, John Wiley & Sons, 76) Inventor: Harold Narcus, 15 Vesper St., pp. 710-725, c 1974. Worcester, Mass. 01602 Pushpavanam et al., Finishing Industries, pp. 48-58, Jun. 1977. 21 Appl. No.: 849,165 Primary Examiner-John D. Smith Attorney, Agent, or Firm-Jerry Cohen 22 Filed: Nov. 7, 1977 57 ABSTRACT 51 Int, Cl’...... C23C 3/02 An adherent, bright metallic nickel coating is applied to (52) U.S. C...... 427/277; 204/38 B; the surface of a plastic or other dielectric part (or to a 427/305; 427/306; 427/307; 427/404; 427/430 metal part) by an electroless process comprising, after A; 427/438 suitable pretreatment of said surface, the deposition of a (58 Field of Search ...... 427/404, 305, 438, 430 A, primary electroless nickel possessing special properties 427/306, 307, 277; 204/38 B followed by a secondary electroless nickel of bright appearance with complete elimination of any subse 56) References Cited quent electroplating process usually required to achieve U.S. PATENT DOCUMENTS this brightness. The nickel coating may be limited to 3,212,917 10/1965 Tsu et al...... 427/305 selected surface areas of a coated part by mechanically 3,817,774 6/1974 Kuzmik ...... 427/304 removing portions of the primary coat prior to immer 3,878,007 4/1975 Feldstein et al...... 427/259 sion of the part in a secondary electroless nickel bath. 3,953,624 4/1976 Arnold ...... 427/438 3,959,523 5/1976 Grunwald et al...... 427/404 11 Claims, No Drawings 4,160,049 1. 2 for making the plastic conductive followed by electro BRIGHT ELECTROLESS PLATING PROCESS plating have been commercially successful but have PRODUCING TWO-LAYER NICKEL COATINGS many technical and economic disadvantages. ON DELECTRIC SUBSTRATES From a technical point of view, intricate parts with blind-holes, threads, small diameter holes, slots, recesses BACKGROUND OF THE INVENTION or internal areas do not receive uniform electroplating The present invention relates to nickel coating partic because, by nature, certain plating baths have poor ularly for plastic and other dielectric articles. throwing power; for example, as in the case of chro Electroless or autocatalytic deposition of metallic mium plating, and costly auxiliary anode assemblies, coatings on non-conductive or dielectric surfaces, such O commonly employed in the industry must be used to as plastics, is a well known process with broad applica plate into these extremely low current density areas. tions in diversified industries such as automotive, radio, Excessive plated metal occurs on the high current den television, plumbing, marine, home appliance, etc. sity areas, such as sharp corners, protrusions, etc., while However, for the benefit of clarity to the non-artisan, it little or even no plating takes place in the low current is stated here electroless plating which is the subject of 15 density areas such as grooves, holes, slots, etc. In other this invention and referred to frequently throughout words, uneven thickness of electrodeposits result due to this disclosure requires no electricity for metallic depo the fact that the high current density areas receive more sition while electroplating or electrodeposition requires metal than the low current density areas. its employment. The field is generally described in my Economically, the cost for applying an electroplated book, "Metallization of Plastics' (Reinhold, New York 20 coating to the plastic is much greater because of the 1960), see also the U.S. patents cited below. relatively thick deposits applied to the conductive film Heretofore, the application of the electroless coating of copper or nickel. Excessive metal costs are incurred. to surfaces of substrates following pretreatment of said Furthermore, plastic parts, especially those large in surfaces was followed by the commonly used electro size, require placement on plating racks for acceptable plating or electrodeposition process known to the in 25 electroplating results. Fixture costs and labor for attach dustry particularly electroplated copper, nickel, chro ing the parts to said fixture bring about these additional mium, gold, silver, etc. to achieve bright surfaces for process expenditures. Furthermore, unplated contact decorative or functional purposes. These prior art pro points appear where the parts are held on these fixtures cesses involve chemical etching of the plastic substrate which is highly objectionable in critical industrial appli mainly to improve adherence of metal thereto, then 30 cations. sensitizing and activating this etched surface, applying a There is a need for electroless plating compositions conductive film of silver, copper or nickel in electro and processes producing bright deposits especially in plating of the desired metal upon this conductive film. the decoration of plastics which will overcome the Recent improvements have eliminated the two-step aforementioned disadvantages while still being compat treatment (i.e. 1 - sensitizing and 2 - activating and 35 ible with known commercial procedures. The present replaced it with a one-step pretreatment involving col invention provides said compositions and processes. loidal solutions containing non-noble copper ions or While the application of bright electroless nickel noble palladium ions; then a conductive film of copper deposits, applied in bulk or mass handling, or with rack or nickel is formed and, finally, electroplating metal is handling, is common practice when these deposits are applied. applied to non-ferrous or ferrous substrates, the bright As an example of the non-noble catalyst treatment ness can only be achieved by bright-dipping or polish referred to, the U.S. Pat. No. 4,020, 197 issued to Steffen ing the metal substrate first to obtain these bright elec (Apr. 26, 1977) treats the plastic surface in a solution of troless finishes. Non-conductive surfaces are normally cuprous chloride, acidified with 10-15% hydrochloric impossible to bright dip and polishing of non-conduc acid, followed by hydrolysis of the cuprous (1) com 45 tive surfaces is not feasible since there would be a loss of pound to a hydrous oxide in hot water; then accelera adhesion of the electroless nickel to the nonconductive tion in an alkaline solution of scdium borohydride. In surface due to the absence of mechanical or chemical numerable patents issued to Feldstein such as U.S. Pat. interlocking of the metallic nickel coating. Nos. 3,993,799, 3,993,848, 3,993,801, 3,993,491, It is the principal object of the present invention to 3,993,799 and 3,982,054 also practice the employment of 50 provide an effective and economical process for elec the so-called non-noble metal catalyst for treatment of trolessly applying attractive, bright metallic coatings of non-conductive surfaces. nickel to non-conductive surfaces, particularly a wide As an example of the noble catalyst referred to, a variety of synthetic resins, for example, acrylonitrile patent was issued to Shipley, U.S. Pat. No. 3,011,920 butadiene styrene (ABS), without the necessity of sub (Dec. 5, 1961) in which the nobel metal, e.g., palladium, 55 sequent electroplating or electrodeposition. is applied directly to the dielectric surface in the form of It is a further particular object of the present inven a colloidal solution containing the metal in zero valence tion to provide a process whereby plastic parts, no state. Normally, the metal is formed in the colloidal matter how intricate in shape, form, or design, can re solution by introducing both palladium chloride and ceive a bright nickel coating uniformly deposited stannous chloride into a highly acidified (with hydro throughout the entire part without using costly racking chloric acid) aqueous solution, the palladium ions being and auxiliary anode assemblies to insure this uniform reduced within the solution to this zero valence state by metal thickness in both high and low current density the stannous ions. U.S. Pat. No. 3,672,938 issued June areas. In other words, the object is to provide a process 27, 1972, to Zeblisky and U.S. Pat. No. 3,767,583 issued wherein parts may be processed in bulk or in mass with Oct. 23, 1973, to Fadgen and Saubestre also practice the 65 out the necessity of racking and still receive bright use of the noble catalyst solution. deposits of electroless nickel with complete elimination Processes of the above nature involving pretreatment of the need for electroplated deposits and related bur and formation of a conductive film of copper or nickel dens of process and equipment. 4,160,049 3 4. (3) Neutralize residual etch solution in a dilute sodium SUMMARY OF THE INVENTION bisulfite solution. The process of the present invention is applicable to (4) Rinse in water, the metallic coating, with nickel, of a wide variety of (5) Activate in the one-stage non-noble or noble catalyst dielectric substrates but is best employed commercially 5 solution. to apply bright nickel to plastics such as acrylonitrile (6) Rinse in water. butadiene styrene (ABS). Other non-conductive sub (7) Accelerate in an alkaline sodium borohydride or strates described in the prior art, including the broad dilute fluoboric acid solution. range of thermoplastic and thermosetting resins, glass, (8) Rinse in water. ceramics, etc., may be suitably electrolessly coated with 10 (9) Apply the Primary Electroless Nickel (foundation nickel in accordance with the present invention. In metal). practice, these substrates are surface conditioned or (10) Apply the Secondary Electroless Nickel (bright etched in the manner known to the artisan prior to the deposit). electroless process in order to improve the adherence of the metallic nickel. The etched substrate is then sensi 15 Examples 1 and 2 which follow are more specific tized and activated in a one-stage or two-stage process illustrative (non-limiting) detailed descriptions of prac (preferably one-stage) utilizing the noble or non-noble tice of the present invention as applied to plastic radio activator or catalyst previously discussed. The pre knobs molded in a platable grade of acrylonitrile treated substrate is then coated with electroless nickel, butadiene styrene (ABS). All solutions and baths are termed in this invention, the Primary Electroless 20 aqueous. Nickel, applied from a special composition to produce a dense, levelled electroless nickel deposited in proper EXAMPLE 1. thickness to act as a suitable foundation metal for re (1) Etch the part in the conventional chromic acid ceiving a Secondary Electroless Nickel possessing at sulphuric acid solution of the following composition: tractive brightness. This combination of a primary and 25 Chromic Acid (CrO3 - 184 grams/liter secondary electroless nickel gives a resulting bright, Sulphuric Acid (H2SO4) (66' Be) - 368 grams/liter attractive uniform deposit to the plastic substrate. No Fluorad FC-95 - 1 gram/liter subsequent electroplating such as with electroplated Fluorocarbon surfactant copper, nickel, chromium, as necessary in the prior art, Treatment - 5 minutes at 65-70' C. is further required in the present invention. 30 (2) Water rinse Parts of the primary electroless nickel coating may be (3) Neutralize mechanically removed prior to applying the secondary Sodium bisulfite (Na2S2O4.2H2O) - 150-200 grams/- nickel coating by immersion of the substrate in the sec liter ondary nickel bath. The secondary nickel coat (over 35 Treatment - 1 minute at 25-30 C. layer) is produced only in those substrate surface areas (4) Water rinse having primary nickel underlayer. (5) Activate (non-noble catalyst) The secondary nickel coat can be supplemented by Acidified cuprous chloride solution (CuCL-HCL) other metal coatings. Treatment - 15 minutes at 40 C. Supplied by - Koll The primary nickel bath is maintained basic 8.0 morgan Technologies, Inc. (Dallas, Texas) or Surface -10.0pH preferably 8.5-9.0 and the secondary nickel Technologies, Inc. (Princeton, N.J.) bath is maintained acidic 4.0-6.0 pH, preferably (6) Hot water rinse - 5 minutes 4.5-5.5. (7) Acceleration In both the primary and secondary nickel coating Sodium borohydride (NaBH4) - 1 gram/liter baths, solutions of nickel salts in polar solvents (prefera 45 Sodium hydroxide (NaOH) - 1 gram/liter bly aqueous) are employed together with a source of Fluorad FC-95 surfactant (1% solution) - 1 ml/liter phosphorous, preferably alkali metal or ammonium Treatment - 10 minutes at 30 C. hypophosphite producing a nickel-phosphorous alloy in (8) Water rinse the final product throughout both primary underlayer (9) Primary Electroless Nickel Bath Immersion coat and the secondary underlayer coat. 50 Nickel Sulphate (NiSO4.6 H2O) - 45 grams/liter The resultant product is characterized by high reflec Ammonium chloride (NH4CL) - 30 grams/liter tivity and adhesion. Sodium citrate (Na3C6H5O7.2H2O) - 5 grams/liter Other objects, features and advantages of the present Glacial acetic acid (CH3COOH) - 10 grams/liter invention will be apparent to those skilled in the art Sodium hypophosphite (NaH2PO2.H2O) - 40 from the following detailed description of preferred 55 grams/liter Ammonium hydroxide (NH4OH 26' Be - 45 embodiments thereof. grams/liter DETAILED DESCRIPTION OF PREFERRED Operating Conditions EMBODIMENTS Temperature 25-30 C. More specifically, the improved process of the pres 60 pH 8.5-9.0 ent invention is comprised of the following sequence of Time - 10 minutes steps used, for example, with acrylonitrile-butadiene styrene (ABS) which is selected because of its excellent (10) Secondary Electroless Nickel Bath Immersion platability: Nickel sulphate (NiSo.6H2O) - 20 grams/liter 65 Lactic acid (80%) (CH3CHOH.COOH) - 30 (1) Surface condition or etch the ABS using the conven grams/liter tional chromic acid-sulphuric acid aqueous solution Propionic acid (CH3CH2COOH) - 2 grams/liter (2) Rinse in water. Lead acetate (Pb 2.3H2) - 0.001 grams/liter 4,160,049 5 6 Sodium hypophosphite (NaH2PO2.H2O) - 25 or air agitation and continuous filtration of the baths grams/liter which are preferred conditions. Operating Conditions It is important to point out that the primary and sec Temperature - 70°-90° C. ondary nickels shown in Examples 1 and 2 must be pH 4.5-5.5 employed jointly for the best practice of this invention. Time 20-30 minutes Using only the primary electroless nickel will produce a dull or, at best, a semi-bright deposit while the employ EXAMPLE 2 ment of only the secondary nickel will give a bright but Steps (1) through (4) - same as in Example 1. Then: less adherent coating of nickel with possible deforma (5) Activate (Noble catalyst): Catalyst #9-A of Ship 10 tion of certain thermoplastic substrates due to the high ley Company, Wellesley, Mass. or Enthone Activator temperature of operation of this bath. Furthermore, #442 of Enthone, Inc., New Haven, Conn. using only the secondary nickel will produce a highly (6) Water Rinse stressed, brittle deposit with a tendency towards flaking (7) Acceleration: 10% (by volume) Fluoboric Acid and peeling, Hence, in the practice of this invention, (HBF4). Treatment: : - 1 minute at 25-30 C. 15 there is the necessity of a so-called DUAL NICKEL (8) Water Rinse SYSTEM, as described herein, wherein the primary (9)-(10) The primary electroless and second electro electroless nickel acts as a foundation eliminating the less nickel compositions are the same as in steps (9) and aforementioned problems. (10) in Example 1. The primary nickel is a smooth or levelled, dense or The pH values for the primary and secondary elec 20 close-grained, pore-free deposit adherent to the prop troless nickel compositions shown in Steps (9) and (10) erly pretreated plastic substrate and tolerant to drag-in of Examples 1 and 2 must be held within the limits impurities from the pretreatment solutions. indicated for distinct advantage and are preferably con The secondary electroless nickel has self-building trolled with 1:1 ammonium hydroxide solution for rais brightness; i.e., the thicker the coating, the brighter the ing the values and a 25% sulphuric acid (by volume) for 25 deposits. If desired, this bright coating can be coated lowering the values. further electrolessly with electroless chromium, gold, The deposits of electroless nickel derived from both silver, copper, etc. to achieve different shades of depos the primary and secondary electroless nickels prefera its other than the color characteristic to electroless bly comprise alloys of nickel and phosphorus (6-12% nickel. This is obvious to the skilled artisan. P) with an approximate average value of 7% phospho 30 Within the scope of this invention is an important rus through use of hypophosphites in the primary and industrial process of selective electroless coating made secondary baths. The actual percentage of phosphorus possible only by utilization of the process disclosed depends on the age of each bath. above. The hardness of the two layer deposit - VICKERS An automotive radio knobs, for example, molded out DPH - shows a microhardness of 400-600 (average 35 of black ABS material is electrolessly coated with the 500 VICKERSO - 49 ROCKWELL C. Reflectivity primary electroless nickel described above. The center values of the overlayer (secondary nickel) are on the section of this knob is machined on a wood turning lathe order of 80-90% in the secondary if properly main or similar equipment (e.g., on a Miller, shaper, grinder) tained. By maintaining a high degree of purity, espe to remove the thin layer (0.000010 - 0.00015') of this cially in the secondary nickel, the bath has long life. Its ductile, machinable primary nickel from this center brightness, under ideal conditions, is exceptional since, section of the knob to expose black plastic. The part in prior art, electroless nickels were not considered as then receives the bright secondary electroless nickel by bright as deposits obtained from electrolytic or electro immersion in a secondary nickel bath. The net result is plated nickels. a bright automotive knob metallized all over with This brightness in the secondary electroless nickel is 45 bright electroless nickel except at the center section obtained by using commercially available, proprietary where the originally molded black ABS plastic is ex brighteners of the type used in electrolytic bright nick posed. In other words, an attractive combination of els. In prior art, brighteners of this type have not found metal and plastic is achieved. significant utilization in electroless nickel deposition. The intermediate machining step obliterates surface Brighteners used in the secondary electroless nickel of 50 activation history in the treated area so that no second Examples 1 and 2 are Udylite 610, 63 supplied by Udy ary nickel adheres to the mechanically treated portion. lite Corp. (Detroit, Mich.) in the order of 0.5%-1% and No finishing steps are necessary. However, the treated 1.5-2.0% respectively. Udylite 62A wetting agent is area should be rinsed. optional but seems to offer certain advantages. Other Prior methods employed to accomplish selective brighteners usually used in electrolytic nickel baths 55 metallizing required the use of costly spray masks or which may be used in the present electroless baths are stencils in conjunction with stop off paints or inks or supplied by Harshaw Chemical Company (Cleveland, silk-screen or photographic procedures as used in Ohio), M&T Chemical (Rahway, N.J.) and Sel-Rex printed circuitry, hot stamping, adhesive-backed in Chemical (Newark, N.J.). serts, two-shot molding, etc. The ductility of the primary electroless nickel is ex Furthermore, since the disclosed process is a total cellent and its metallurgical properties are highly satis electroless method requiring no subsequent electroplat factory for a foundation coating for the applied second ing, costly complex racking for electrical connection is ary electroless nickel. The secondary nickel is bright totally eliminated. Hence, the net result is a low cost but less ductile than the primary nickel but entirely selective plating process. satisfactory for applications in industry. 65 Other applications for selectively decorating plastic The rate of deposition from both the primary and items for the novelty field include selective plating of secondary nickels is 0.0006" to 0.0008" per hour under jewelry items, buttons, placques, etc. A variety of geo properly controlled bath compositions with mechanical metric designs are now obtainable. In mass production, 4,160,049 7 8 automatic cutting machines can be adapted economi 3. The method of claim 1 wherein both the primary cally to remove the primary electroless nickel in the and secondary baths have the same nickel compound predetermined areas prior to the application of the SOTC. bright secondary electroless nickel. 4. The method of claim 3 wherein nickel sulfate com 5 prises said common nickel source. It will be understood that several nickel salts can be 5. Method of nickel coating in accordance with claim used in lieu of nickel sulphate incorporated in the above 1 comprising, examples - e.g., nickel chloride, nickel acetate, nickel etching and activating the substrate surfaces in a ammonium sulphate. Brighteners used include many single step, organics, e.g., naphthalene sulfonic acid, and inorganic, 10 acceleration treatment of the substrate surfaces, e.g., cobalt sulphate compounds and are, per se, well immersing of the substrates in a primary nickel solu known in the art. The phosphorous compound used as a tion maintained at 25'-30 C. and pH of 8.5-9.0 for reducing agent may be replaced in whole or part by a 5-15 minutes to produce a foundation nickel coat boron compound, e.g., dimethylamineborane (DMAB) ing therein, or sodium borohydride, resulting in boron instead of 15 and then immersing the substrate without rinsing or phosphorous included in the resulting coating. neutralization, or taking into a secondary, different, Although the invention has been described and illus nickel solution maintained at 70°-90° C. and 4.5-5.5 trated in detail, it is clearly understood that the same is pH to produce a self building brightening of the by way of illustration and example and is not taken by substrate surfaces. 20 6. Method of nickel coating in accordance with claim way of limitation, the spirit and scope of this invention 5 wherein the secondary nickel treatment is supple being limited only by the terms of the appended claims mented by deposition of at least one additional metal. which follow. 7. Method of nickel coating in accordance with claim What is claimed is: 5 wherein a portion of the foundation coating is re 1. Method of producing adherent, decorative, two 25 moved prior to the said second immersion of the sub layer nickel coatings on dielectric substrates compris strates into nickel solution. 1ng, 8. Method in accordance with claim 5 wherein said activating the substrate surface, primary nickel solution comprises nickel sulfate and electrolessly depositing a first dull nickel alloy layer sodium hypophosphite and a basic mixture including thereon comprising 6-12% phosphorus, balance 30 glacial acetic acid and ammonium hydroxide and said essentially nickel, in a first electroless coating bath, secondary nickel solution comprises nickel sulphate, the layer being dense and levelled, sodium hypophosphite and a weak acid mixture. and subsequently producing a second nickel-phos 9. Nickel coating method in accordance with claim 1 phorus alloy layer of self building brightness over wherein the second bath is carried out at lower temper the first layer by electroless coating in a second, 35 ature than the first bath, wherein the coating steps are controlled so that the second layer is thicker than the different electroless coating bath, first coating layer and wherein the pH of said first bath the second bath also producing a 6-12% phosphorus, is controlled to be 8.0-10.0 and that of the second bath balance essentially nickel, composition, to be 4.0-60. and wherein the coating rates in both the first and 10. The method of claim 9 wherein the first bath is second baths are controlled to be 0.0006'- 0.0008' maintained at under 50 C. and the second bath above per hour with the first layer coating stepbeing long 50 C. and substantially above the temperature of the enough to produce an adherent 0.000010"-0.00015" first bath. thickness (i.e., 2500-37,500 Angstroms) first layer 11. Nickel coating method in accordance with claim and the second layer coating being carried out long 45 1 wherein selected area portions of the first coating enough to produce a second coating layer which is layer are removed by machining prior to exposure of even thicker than the first coating layer. the first-layer-coated substrate to the second bath 2. The method of claim 1 wherein the two coating wherey the second coating layer is not produced in the baths contain MH2OP2. H2O where M is selected from machined surface areas. the class consisting of alkali metal and ammonium ions. 50 k it is

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