Patent GB-1185954-A (GB)
Title: Improvements in the Plating of Metal on Plastics Materials
Inventor: HEPFER IVAN C
IPC: C23C18/30
Filed: 1968-01-23
Abstract: 1,185,954. Electroless deposition of metals. MACDERMID Inc. Jan.23, 1968, No. 3460/68. Heading C7F. A non-conductive, e. g. plastics substrate which is to be plated with a metal is first, after an initial cleaning if required, mechanically or chemically etched, then is cleaned in water or an aqueous solution and immersed in an aqueous solution of a noble metal salt, with a molar concentration equivalent to that given by 0À25 to 10À0 grams of PdCl 2  per gallon of solution, containing 0À5 to 20 mls. of specific gravity 1À191 per gallon and at 70‹ F. to 212‹ F. The initial cleaning may be by alkaline soak cleaning, by cleaning with a solvent or by use of a sulphuric acid-chromic acid cleaner, and is intended to remove mould release compounds or machining oils. The parts to be treated are, when clean, tumbled in a barrel with a fine abrasive or are subjected to wet or dry blasting with fine abrasives, in either case with a mild acid dip following, or plastics parts are etched in a bath comprising by weight:- Sulphuric acid (conc. 66‹ Be 77À0-92À0% H 2  SO 4  ) Chromic acid flakes (CrO 3 ) 0À10-4À72% Water 21À5-6À0% Fluorocarbon surface active 0À01-0À2% agent (if reqd.) at 70-160‹ F. and a density of 57À0-63À0‹ Baume for ¢-30 minutes, then are water rinsed. Parts with deep blind holes may be given an alkaline rinse followed by an acid dip, e. g. in hydrofluoric, sulphuric or hydrochloric acid. After etching and rinsing the parts are immersed in an activating aqueous bath of a noble metal salt, e.g. of a Pd salt or of a mixture of noble metal salts, e.g. Pd and Au salts, comprising:- Noble metal salt (PdCl 2  or other  similar molar cone.) 0À25-10À0gm/ gal. Hydrochloric acid (specific gravity 1À191)(>1ml/gm. above salt) 0À5-20À0ml./gal. Boric acid (H 3  BO 4 ) (optional) (pH buffer) 1À5-175 gm. / gal. Max. range pH (adjusted with NaOH or KOH and H 2 SO 4 ) 1À0-4À8 at 70‹ -212‹ F. for ¢-5 minutes, then are water rinsed. They may then be plated with Ni in a bath comprising: - Ni sulphate (NISO 4 . 6H 2 O) 5-20 gm./1. Na hypophosphite (NaH2   PO 2 ) 5-30 gm. /1. Na salt of an organic acid (buffer) 7À5-37-5 gm./l. Stabilizer 1-50 p. p. m. by weight. pH (adjusted with sulphuric acid and NH 4  OH) 3À5-5À0  at 140‹ -185‹ F. Ni chloride, Ni formate, Ni citrate, Ni acetate or Ni sulphamate may replace Ni sulphate, in concentrations which allow for molecular weight variations, and in place of sulphuric acid to adjust the pH acetic, formic, citric, hydrochloric, boric, glycolic or gluconic acid may be used. Suitable stabilizers are one or more of Na thiosulphate, thiourea, diethyl thiourea, molybdic acid, other Mo compounds tungstic acid, H peroxide, ammonium persulphate, Cd salts, Sn salts and Pb sulphide. No wetting agent is used in the bath. If desired two plating baths may be used in succession, so that carry-over of the activating solution can affect only a small volume of solution in the first bath. After electroless Ni plating the parts may be electrolytically plated with Cu and/ or Ni and then with a final coating of Ni, brass, Au or Cr. In place of electrolessly deposited Ni, the parts may be electrolessly coated with Cu, either by placing them, after etching and water rinsing, first for 10-180 seconds in a 0À01- 10À0% by weight aqueous solution of Na hypophosphite at 70‹ -90<SP>‹</SP> F., then for 1-20 minutes in a bath comprising:- Cu sulphate (Cuso 4 . 5H z  O) 15-40 gm. / 1.  Rochelle salts (Na KC 4  H 4  O 6 . 4H 2 O) 40-140 gm./l. Nahydroxide (NaOH) 8-39 gm./l. Soda ash (Na 2 CO 3 ) 10-35 gm./l. Tetra sodium-ethylene diamine 2-15 gm./l. Tetra acetate Formaldehyde (37% by weight HCHO) 10-150 ml./1. Stabilizer (as for Ni bath) 1-100 p. p. m. by weight at 70‹ -90‹ F. Plastics materials which may be coated include ABS, nylon, lucite, SAN cendacetal resins.