US3733213A - Electroless plating of plastics and fibers - Google Patents

Abstract

NYLON DACRON OR OTHER FIBERS OF RABRIC IS PLATED BY FIRST DEGREASING THE FIBRIC WITH AN ORGANIC SOLVENT SUCH AS METHYL ETHYL KETONE, THE FIBRIC IS THEN IMMERSED IN A NOVEL NON-AQUEOUS SOLUTION WHICH SIMULTANEOUSLY FURTHER DEGREASES, CLEANS AND WETS, ETCHES AND INITIATED SENSITIZATION OF THE SURFACE O THE FABRIC FIBERS, THE FABRIC IS THEN RINSED AFTER WHICH IT IS DEGLAZED BY IMMERSION IN AN OXIDIZING SOLUTION, RINSED, IMMERSED IN AMMONIA SOLUTION, TREATED IN A NOVEL SENSITIZING SOLUTION, ACTIVATED IN A NOVEL ACTIVATING SOLUTION, RINSED AND PLATED IN A NOVEL NICKEL OR COPPER PLATING SOLUTION. THE FABRIC MAY BE FURTHER PLATED BY ELECTROPLATING TECHNIQUES.

Description

United States Patent 3,733,213 ELECTROLESS PLATING OF PLASTICS AND FIBERS George Jacob, Flourtown, Pa., assignor to Coppertech Inc., Flourtown, Pa. No Drawing. Filed Dec. 31, 1970, Ser. No. 103,296 Int. Cl. C23c 3/02 US. Cl. 117-47 A 9 Claims ABSTRACT OF THE DISCLOSURE Nylon, Dacron or other fibers or fabric is plated by first degreasing the fabric with an organic solvent such as methyl ethyl ketone, the fabric is then immersed in a novel non-aqueous solution which simultaneously further degreases, cleans and wets, etches and initiates sensitization of the surface of the fabric fibers, the fabric is then rinsed after which it is deglazed by immersion in an oxidizing solution, rinsed, immersed in ammonia solution, treated in a novel sensitizing solution, activated in a novel activating solution, rinsed and plated in a novel nickel or copper plating solution. The fabric may be further plated by electroplating techniques.

BACKGROUND OF THE INVENTION The present invention relates to electroless plating of nylon or Dacron and particularly to electrolessly plating nylon and dacron fabrics with nickel or copper.

Chemical plating solutions for depositing metals by autocatalytic chemical reduction of metal ions in solution and in contact with a catalytic surface of the article to be plated are well known. Such solutions, which do not use electricity, are referred to in the art as electroless plating solutions. Electroless metal deposition is also distinguished from displacement metal plating of the type described in Metals Finishing Guide Book, 27th edition, 1959, pages 469 et seq., and metal mirror procedures. Electroless metal plating has found particular use in plating non-metallic substrates such as ceramics and plastics.

Typically, electroless metal depositions of a non-metallic substrate comprises the separate steps of degreasing the substrate, wetting the substrate by immersion in an aqueous detergent solution, oxidizing or deglazing the substrate, sensitizing the surface of the substrate in an aqueous stannous salt bath, rinsing thoroughly, activating the surface in a catalytic noble metal salt solution such as palladium chloride and finally plating the activated substrate in an electroless plating bath. The substrate may then be electroplated to build a thick coating if desired.

While the general technique is well known, the particular steps and compositions of solution useful in the process vary depending upon both the chemical and physical nature of the substrate to be coated. One set of solutions or conditions for electroless plating may result in a commercially useful product for one substrate but not for another. Among the requirements for commercial utility are: solution stability; reproducibility; good adhesion of the deposit; uniformity of deposit for subsequent electrolytic metal plating; and the production of high luster of the plated metal.

Electroless plating of nylon and Dacron fabrics with prior art techniques have not resulted in commercially useful materials. The requirement for uniformity of coating and good adhesion free of chipping, peeling or flaking especially after electroplating over the electroless metal deposit is particularly stringent for plating of fabrics which are generally subject to deformation and stress during use and which possess a much larger surface area as compared with solid block material.

I have developed a process which is particularly useful for the electroless plating of fibers and fabrics of nylon,

'ice

Dacron, rayon, silk and fiberglass with nickel or copper which leads to superior commercially useful products. The novel process is also less costly than similar prior art processes and produces smoother, more uniform and more adherent and bright coatings on these substrates. The novel process is, of course, also useful in the plating of these and chemically similar materials in a form other than fibers or fabrics.

SUMMARY OF THE INVENTION A process for electrolessly nickel or copper plating materials comprises; treating the material in a non-aqueous solution which simultaneously degreases, cleans, wets, etches, and initiates sensitization of the substrate material; deglazing the substrate material in an acid oxidizing solution; rinsing and neutralizing the surface of the material; sensitizing the surface of the material with a sensitizing solution containing a non-ionic detergent, a stannous salt and an organic reducing agent all dissolved in a nonaqueous solvent; activating the material in an aqueous solution of palladium chloride; and electrolessly plating the fabric with nickel or copper.

The process is particularly useful for the plating of fibers or fabrics of nylon, Dacron, rayon, silk and fiberglass. Nylon is a polyamide generally produced from the polymerization of an adipic acid derivative; Dacron is a polyester produced from the polymerization of the condensation product of ethylene glycol with hexamethyl terephthalate; rayon is a cellulose based fiber generally either cellulose acetate or regenerated nitrocellulose.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The novel process comprises the steps of:

While it is essential to utilize the combination of the various novel solutions referred to above in order to obtain optimum commercially useful coatings on nylon and Dacron fabrics, these novel solutions are individually useful for improving the plating of materials other than nylon or Dacron. For example, the various novel solutions aid in improving coatings of such materials as polyethylene, polypropylene, polystyrene, polysulfone, epoxy, phenolics, acrylics, vinyls and polyimides and are useful as substitutes for prior art solutions performing similar functions in electroless plating of these materials.

In practice, rinsing steps are generally preferably employed between all other process steps. Also, if the fabric is excessively oily, greasy or otherwise dirty it may be desirable to degrease the fabric with a conventional degreasing solvent, or methyl ethyl ketone, prior to immersion in the novel non-aqueous multiple acting solution referred to in step (1) supra. This multiple acting solution comprises an organic solvent having stannous chloride and a non-ionic detergent, such as commercially available Triton X-lOO, dissolved therein. The solvent must not only be capable of dissolving the stannous chloride and detergent but should also be a good solvent for organic contaminants and capable of etching the fabric surface. The preferred solvent is dimethyl formamide. An

optimum composition for this multiple acting solution comprises:

Dimethylformamide /2-1 /z gallons Stannous chloride 100-450 grams Triton X-100 detergent 1-10 cc.

This solution is also useful for obtaining improved electroless plating of polyesters such as mylar, and plating of polyethylene and polyimides. Use of this solution prior to deglazing or oxidizing the substrate is essential for commercially useful results. While the complete action of this solution on the fiber or fabric substrate is not fully understood, it is believed that a tin-organic layer is formed on the surface of the substrate which enhances sensitization after the deglazing step.

A preferred oxidizing solution useful in the novel process comprises:

Water 400-800 cc. Sulfuric acid 200-800 cc. Chomic acid 30-100 grams The novel sensitizing solution of the novel process is identical to the multiple acting solution referred to above. However, optimum results are achieved when from 1 to 20 weight percent formaldehyde is added to the solution. The formaldehyde may be added as a solid or it may be added as an aqueous solution or non-aqueous solution. For example -40 volume present of a 48% formaldehyde solution may be added. These solutions are also useful for sensitizing materials other than the named fabric materials.

The novel aqueous activating solution comprises palladium chloride in hydrofluoric acid. A preferred composition is:

Water /:-1 /2 gallons Palladium chloride 0.1-l /2 grams/gallon Hydrochloric acid: 500-1000 cc. 12 N H L/ gal. Concentrated hydrofluoric acid /gogallon Prior art activating solutions contained no HF and it is the inclusion of HF which aids in giving rise to the improved, uniform activation obtained with the novel solution. While the inclusion of HP is preferred it is not essential except where the fabric to be plated is nylon. Without HP in the activator, the adhesion of the electroless metal and its uniformity on the substrate is extremely poor.

While commercially available electroless nickel or copper plating can be employed, it is preferred in order to obtain optimum results to use a novel nickel bath or a novel copper bath as set forth in the examples given below.

Subsequent to electroless plating, the fabric may be further plated by conventional electroplating techniques to build up a thick metal layer. Such fabrics have many uses including bullet proof vests, RF shields, static discharge clothes, decorative clothes, heaters and large area chemical catalysts or electrodes.

EXAMPLE 1 A nylon fabric to be plated is first degreased by immersion in methyl ethyl ketone (MEK) to eliminate any heavy oil formation on the fabric. It is believed that the MEK treatment may also dehydrate the substrate surface. This is desirable. The fabric is then immersed in the multiple acting solution for 3-6 minutes at room temperature. The particular solution consists of 200 grams of stannous chloride and 5 cc. of Triton X-100 anionic detergent in 1 gallon of dimethylformamide. The fabric is then rinsed in water and deglazed by immersion for 2-5 minutes at room temperature in an oxidizing solution consisting of 70 grams of chromic acid dissolved in 600 cc. of water and 500 cc. sulfuric acid. The fabric is then rinsed by immersion for 3-5 minutes in a 50% aqueous solution of concentrated reagent ammonium hydroxide to neutralize any excess acid. This rinse is fol- ,4 lowed by a water rinse. The fabric is then sensitized by immersion in the multiple acting solution described above. The fabric is then thoroughly rinsed prior to the next step. The fabric is now ready for activation by immersion for 1-6 minutes at room temperature in an activating solution consisting of 1 gram of palladium chloride dissolved in a mixture of 4 gallon of concentrated hydroflouric acid, /2 gallon concentrated hydrochloric acid and 1 /8 gallons of Water. The activated fabric is then thoroughly rinsed and is finally plated with either nickel or copper.

A preferred and novel electroless nickel plating bath comprises both nickel and gold ions in solution which codeposits gold together with nickel on the substrate. A useful formulation consists of 300 grams NiCl per gallon of solution. 200 grams per gallon citric acid; 190 grams per gallon lactic acid; 40 cc. per gallon propanoic acid; 1 gram per gallon non-ionic detergent; 50 grams per gallon sodium hypophosphite and /2 grain of gold per gallon either as AuCl or potassium gold cyanide. The remainder of the solution is water. The solution is brought to a pH of from about 7-9 with ammonia. The preferred operating temperature of this bath is between about F.120 F. Plating of a sufiicient thickness is obtained in from about 15-30 minutes. The combination of the named organic acids and gold ions together with the nickel ions of the bath are important in yielding supenor coatings.

A preferred novel copper plating bath comprises a copper solution containing in combination ethylene diamine tetraacetic acid (EDTA), lactic acid and sodium carbonate. This combination provides improved stability of the plating solution and enhances ductility, adhesion and brightness of the deposit. The concentration of EDTA and lactic acid should be 20 to 30 grams per gallon of EDTA and between 20-30 grams per gallon lactic acid. Generally, if only EDTA, lactic acid or sodium carbonate is used in the absence of each other the bath is either unstable and/or the rate of deposition is sluggish and/or the deposit is of poor quality. The copper plating bath is best prepared by combining equal volumes of two solutions. The first solution comprises:

15-25 gallons deionized water 3-9 gallons NaOH (50% solution) 7-20 pounds tartaric acid 15-16 pounds paraformaldehyde 2-6 oz. cobalt sulfate or cobalt acetate 6-18 pounds copper sulfate The pH is adjusted to 6.6-6.7

The second solution comprises:

10-20 gallons water 10-30 gallons sodium hydroxide 2.5-7 lbs. per gallon sodium carbonate 7-21 pounds tartaric acid 2-6 pounds lactic acid/EDTA 2/ 3-3/ 2 ratio 50-150 cc. Triton X- What I claim is:

1. An electroless plating process comprises the steps of: (a) treating a surface of a material to be plated, said material being capable of being wetted and etched by dimethyl formamide, in a non-aqueous solution comprising a non-ionic detergent and stannous chloride both dissolved in dimethyl formamide; (b) treating the surface with an acidic oxidizing solution; (c) neutralizing the surface with a basic solution; (d) sensitizing the surface in a sensitizing solution containing in combination, a non-ionic detergent and a stannous salt dissolved in nonaqueous solvent; (e) activating the sensitized surface in an aqueous palladium chloride activating solution; (f) rinsing the surface to remove excess activating solution;

(g) electrolessly plating the activated surface by immersion in an electroless plating solution.

2. An electroless plating process useful for plating substrates of polyamides, polyesters produced from the polymerization of the condensation product of ethylene glycol with hexamethyl terephthalate, rayon and silk with nickel or copper comprises the steps of: (a) treating the substrate to be plated in a non-aqueous solution comprising in combination, a non-ionic detergent and a stannous salt both dissolved in a non-aqueous solvent, said solution simultaneously cleans, wets, etches and initiates sensitization of said substrate; (b) treating said substrate with an acidic oxidizing solution; (c) treating said substrate in a solution to neutralize and rinse said acidic oxidizing solution; (d) sensitizing said substrate in a sensitizing solution comprising the combination of ingredients present in the non-aqueous solution of paragraph (a) together with an organic reducing agent; (e) activating the sensitized substrate in an aqueous activating solution comprising palladium chloride and hydrofluoric acid; (f) rinsing said activated substrate, and ('g) clectrolessly plating said activated substrate by immersion in an electroless plating solution.

3. The process described in claim 2 wherein said nonaqueous solution of paragraph (a) comprises a non-ionic detergent and stannous chloride dissolved in dimethylformamide and wherein the organic reducing agent in said sensitizing solution is formaldehyde.

4. The process described in claim 2 including the step of degreasing said substrate with methyl ethyl ketone prior to treatment with said non-aqueous solution.

5. An electroless plating process for electroless plating of nickel or copper on a substrate of a polyamide, a polyester, a cellulose derivative, silk and fiberglass comprises the steps of:

(a) treating the substrate to be plated in a solution consisting essentially of the following proportions of materials, /2 to 1 gallons dimethylformamide, 100-450 grams stannous chloride and a non-ionic detergent;

'(b) treating said substrate with an acidic oxidizing solution;

(c) neutralizing and rinsing the oxidizing solution from said substrate;

(d) sensitizing said substrate in a sensitizing solution consisting essentially of materials in the following proportions; /z-1 /2 gallons dimethylformamide,

-450 grams stannous chloride, a non-ionic detergent and -1 to 2-0 weight percent formaldehyde;

(e) rinsing said substrate;

*(f) activating said substrate in a palladium chloride activating solution;

(g) rinsing said substrate; and

(h) metallizing said substrate with an electroless metal plating bath.

6. The process described in claim 5 wherein said activating solution consists essentially of materials in the following proportions;

to 1 /2 "gallons Water 0.ll /z grams/ gallon palladium chloride 500-1000 cc. 12 N hydrochloric acid/ gallon /2 gallon concentrated hydrofluoric acid solution.

7. The process described in claim 5 wherein said metal plating bath is a copper plating bath.

8. The process described in claim 5 wherein said metal plating bath is a nickel plating bath.

9. The process described in claim 8 wherein the nickel plating bath co-deposits gold.

References Cited UNITED STATES PATENTS 3,425,946 2/1969 Emons et al 117-47 AX 3,442,683 5/1969 Lenoble et al. 117-47 A RALPH S. KENDALL, Primary Examiner US. Cl. X.R.