GB2040970A

GB2040970A - Conditioning of Caprolactam Polymers for Electroless Plating

Info

Publication number: GB2040970A
Application number: GB7938565A
Authority: GB
Original assignee: Crown City Plating Co
Current assignee: Crown City Plating Co
Priority date: 1978-12-19
Filing date: 1979-11-07
Publication date: 1980-09-03
Also published as: FR2444692B1; JPS639019B2; IT7928066A0; CA1125630A; GB2040970B; JPS55100972A; IT1193252B; FR2444692A1; DE2948133A1

Abstract

Caprolactam polymeric substrates are conditioned for electroless plating by etching with an aqueous solution of organic acid containing from 2 to about 10 carbon atoms, preferably an acetic acid compound, such as trichloroacetic acid.

Description

SPECIFICATION Conditioning of Caprolactam Polymers for Electroless Plating Abstract of the invention Caprolactam polymeric substrates are conditioned for electroless plating by etching with an aqueous solution of organic acid containing from 2 to about 10 carbon atoms, preferably an acetic acid compound, such as trichloroacetic acid.

Background of the Invention The present invention relates to electroless plating of caprolactam polymers in particular, to provide a surface uniformly receptive to electrolessly deposited nickel and copper.

The benefits of electroless plated, nonconductive articles, particularly plastic articles, are well known. In the finished product, the desirable characteristics of the plastic and the metal are combined to offer thereby the technical and aesthetic advantages of each.

Polymeric substrates are conventionally plated by pre-etching the surface by contact with an aqueous solution of at least one organic compound active for conditioning the surface of the plastic, then etching with a strong oxidizing acid or base, seeding the surface with a noble metal catalyst, e.g., a palladium chloride solution, then immersing the seeded surface in an autocatalytic electroless solution where an initial coating of a conductive metal, e.g., copper or nickel, is established by chemical deposition. The metal deposit acts as a buss to allow a thicker coating of metal to be built up electrolytically.

Attempts to adapt conventional procedures for electroless plating of polymers to polyamides by us have resulted in a failure to achieve a uniform adherent coat of metal. Having found conventional electroless plating procedures ineffective, a quest was initiated to discover a procedure to enable uniform coating of polyamides with electroless deposited metals.

Summary of the Invention It has now been found that electroless plating of caprolactam polymers, particularly filled caproiactam polymers, can be realized by contacting a caprolactam polymer substrate with an aqueous solution comprising an organic acid containing from 2 to about 10 carbon atoms and soluble in water to a concentration of at least 3 percent by weight. Contact is for a time sufficient to render the surface receptive to a metal catalyst It is presently preferred to employ a solution comprising at least one acetic acid compound of the formula:

wherein each X is independently selected from the group consisting of hydrogen, hydroxyl and halogen.

This is followed by seeding the surface with a metal electroless plating catalyst selected from solutions of noble metal ions and colloidal suspensions or dispersions of noble or non-noble metal particles.

Following seeding and activation of the metal catalyst by conventional means, the surface can be uniformly plated with electroless copper or nickel.

Contact time in fhe organic acid etch is normally from about 10 seconds to 1 5 minutes at room temperatures. Concentration of the acetic acid compound is normally at least about 3 percent by weight of solution up to solution saturation, preferably from about 5 to about GO percent by weight.

In carrying out the process, an alkali solution having a pH of at least about 10, may be used to condition the substrate and if used, is preferably employed at a temperature from about 1 500F to the boiling point of the solution or the softening point of the plastic, whichever is less, preferably 170 to about 2000F at contact times ranging from about 0.5 to about 20 minutes or more, depending on temperature and alkali concentration. Concentration is normally from about 2 percent by weight of solution to solution saturation, preferably from about 10 to about 50 percent by weight. It is preferred to employ a solution of an alkali metal hydroxide such as sodium or potassium hydroxide.

In conducting the process of the invention, the article may be pre-conditioned by contacting the article in an aqueous solution of an organic solvent, preferably an alkali soluble organic solvent for the caprolactam polymer in a concentration up to about 2 percent by weight, preferably up to about 1 percent by weight.

Ethylene glycol, phenolic compounds such as chlorophenoi, cresols and salts thereof are presently preferred. The solvent may be contained in its own bath or included in the alkali solution so long as the alkali does not hydrolyze or otherwise degrade the organic solvent. The solvent serves to soften the plastic to acid etch. Contact with the solvent solution is prior to contact with the acid etch and may be, if used, be prior to contact with the alkali solution.

in addition, the substrate after contact with the solution of the acetic acid compound may be further conditioned to remove surface debris of the etching by contact with acidic to basic wash.

Detailed Description According to the present invention, there is provided a process which enables uniform electroless deposition of metals onto substrates formed from caprolactam polymers, typically filled substrates.

The process of the invention requires contacting the caprolactam article with an etch solution comprising an organic acid compound containing from 2 to about 10 carbon atoms and having a solubility in water of at least 3 percent by weight of the solution, and contact is for a time sufficient to render the surface uniformly receptive to a metal catalyst. It is preferred to use a solution of an acetic acid compound as defined below.

As part of the process measures, water rinsing with deionized water is performed for good housekeeping between each step. The substrate may be pre-treated with a dilute solution of solvent for the polyamide, preferably an alkali soluble solvent, to soften the surface of the substrate to promote etch. The solvent for the polyamide may be contained in a separate bath or part of the alkaline solution, as herein defined.

In addition, the substrates may be contacted with an acidic or basic solution subsequent to etch to remove debris present on the surface of the substrate.

The caprolactam polymers to be conditioned are known as Nylon 6.

The essential step of the process is contact of the caprolactam substance with an organic etch containing preferably at least one acetic acid compound. The presently preferred etch is one comprising at least about 3 percent by weight of solution, preferably 5 to about 65 percent by weight, and more preferably, from about 10 to about 25 percent by weight of solution of at least one acetic acid compound of the formula:

where each X is independently hydroxyl, hydrogen or halogen, with halogen preferred. Contact is at room temperature, although elevated temperatures may be employed. Contact times range from about 10 seconds to 1 5 minutes or more and are for a time sufficient to etch the surface of the amide to a degree that it becomes uniformly receptive to seeding by a metal electroless plating catalyst.

Among the acetic acid compounds which may be used there may be mentioned trichloracetic acid, acetic acid, hydroxyacetic acid, dichloracetic acid, chloracetic acid, fluoracetic acid, difluoracetic acid, trifluoracetic acid, bromacetic acid, dibromacetic acid and the like.

Trichloroacetic acid is presently preferred.

An optional step of the process is contacting the caprolactam substrate with an aqueous alkaline solution having a pH of at least 10 to condition the surface prior to contact with the acid etch. It is presently preferred that the alkaline solution contain at least one alkali metal hydroxide, such as sodium and/or potassium hydroxide. The alkali employed should be present in a concentration from about 2 percent to solution saturation, preferably from about 10 to about 50 percent by weight.Solution temperature is maintained from about 1 500F to the lesser of the boiling point of the solution and the softening point of the caprolactam substrate, preferably from a temperature of about 1 700F to 2000F. Contact time may vary from about 0.5 to 20 minutes or more, depending upon temperature and the alkali concentration, although it has been found that prolonged immersions will not damage the substrate. Besides the alkali metal hydroxides, there may be employed alkaline compounds such as sodium metasilicate, trisodium phosphate, sodium carbonate and the like, used alone and/or in combination with an alkali metal hydroxide.

There may also be employed as part of the process, a separate bath used alone; preceding or following the alkaline conditioner or included in the alkaline conditioner, of a solvent for the surface of the caprolactam to soften the surface to aid attack by the alkali and/or the etch.

Typically, concentration of the solvent is up to about 2 percent by weight, preferably up to about 1 percent by weight. A wide variety of solvents for polyamides may be used. The presently preferred solvents are ethylene glycol, phenols such as chlorophenol, cresols and the like, and salts thereof. It is presently preferred to precede the acid etch by contact with the solution of the solvent whether or not an alkaline conditioner is used. The solvent serves to soften the surface of the caprolactam substrate to promote conditioning and/or etching.

In addition, subsequent to etch the caprolactam substrate may be brought into contact with an acid or alkaline solution of either an organic or inorganic base to cleanse the surface of debris, i.e., filler and/or degradated resin. Such solutions are normally maintained at room temperature, although elevated temperatures may be employed. Concentrations are in the range up to about 20 percent by weight, preferably up to about 10 percent by weight.

Functional acids include hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid and the like. There may also be employed the alkaline solution used for conditioning as well as salt solutions, such as solutions of borax and ammonium bifluoride. The concentration is that which will enhance surface finish without detracting from the ability of etched surface to accept a metal catalyst.

Whether or not the cleansing treatment is employed, the article is rinsed in water, usually deionized water, and seeded with a metal electroless plating catalyst contained in an aqueous medium. The catalyst may be noble or non-noble metal based. The use of a noble metal catalyst contained in an aqueous medium is preferred. By a noble metal catalyst contained in an aqueous medium, there is meant an ionic solution or colloidal suspension of the free metals.

Colloidal suspensions are preferred. The noble metals include gold, platinum and palladium, with palladium preferred. Suitable non-noble metal catalysts are described in U.S. Patent 3,958,048 assigned to the same assignee as this application and incorporated herein by reference.

A suitable ionic bath is one containing palladium chloride in a concentration of about 0.2 grams per liter solution and 3 ml of concentrated hydrochloric acid per liter of solution. Following seeding, the palladium can be reduced to the free metal state by immersion in a bath of a reducing agent such as dimethyl amine borane.

Colloidal suspensions of noble metals are described in U.S. Patent 3,011,920 to C.R.

Shipley, Jr., incorporated herein by reference. The presently preferred colloidal suspension is one which is about 1.7 molar in hydrochloric acid (HCIl. Such suspensions are colloidal in nature in which the noble metal colloid is maintained in suspension by a protective colloid, i.e., stannic acid colloids. Following seeding, the colloid is removed by immersion in an acidic or alkaline accelerator solution to remove the protective colloid and expose the absorbed noble metal.

Although less preferred, there may also be employed a seeding method which involves contacting the etched article with a sensitizing solution containing stannous chloride followed by immersion in an activator solution, such as a palladium chloride solution, where the ionic palladium is reduced to the free metal on the surface of the substrate.

Suitably activated, the article may be electrolessly plated by conventional means.

Electroless copper and nickel formulations, such as those described in U.S. Patents 3,011,920 and 3,874,072, incorporated herein by reference, may be employed. Electroless copper solutions and typically based on a soluble copper salt, such as copper sulfate, a complexing agent for the cupric ion such as Rochelle salt, an alkali hydroxide for adjustment of pH, a carbonate radical as a buffer and a reducing agent for the cupric ion such as formaldehyde.

Following electroless plating, the substrate may be electrolytically plated by conventional means, with copper, nickel, gold, silver, chromium and the like to provide the desired finish on the article.

Example An article molded of Capron(TM) XPM-1 030, a filled Nylon 6, manufactured and sold by Allied Chemical Corporation, was contacted with a 1 5 percent by weight to volume aqueous solution of trichloracetic acid solution maintained at room temperature for 5 minutes. After rinsing in deionized water, the article was seeded by contact with a proprietary colloidal tin-palladium catalyst, as described in U.S. Patent 3,011,920, at an acid molarity of about 1.7. An alkaline accelerator was used to expose the palladium metal.The catalyst was maintained at about 120"F and the accelerator at about 1 050F. The seeded article was electrolessly plated using Cuposit(TMi PM-990, manufactured and sold by the Shipley Company. The electroless plating solution was maintained at room temperature.

Following electroless plating, the article was rinsed in deionized water, soaked in an alkaline cleaner, passed to a reverse current cleaner, an acid dip, bright acid copper and nickel electrolytic plating solutions, and finally to a chromium plating solution.

The plated article was subjected to a cycle test to determine adhesion performance under thermal stress conditions. In this test, the plated article was maintained at a temperature of 1 800F for 1 hour, then cooled to and maintained at room temperature for 30 minutes then cooled to -200F and maintained at that temperature for 1 hour.

The cynle test was passed.

Claims

1. A process for etching the surface of a caprolactam substrate for electroless plating which comprises etching the caprolactam substrate with an aqueous etch solution comprising at least one organic acid compound containing 2 to about 10 carbon atoms in the compound and soluble in a concentration of at least about 3 percent by weight of solution and present in a concentration sufficient to render the caprolactam substrate receptive to a metal electroless plating catalyst.

2. A process as claimed in claim 1 in which the caprolactam substrate is contacted, prior to contact with the aqueous etch solution, with a dilute aqueous solution of an organic solvent for caprolactam for a time sufficient to soften the surface of the caprolactam substrate.

3. A process for etching the surface of a caprolactam substrate for electroless plating which comprises contacting the caprolactam substrate with an aqueous etching solution comprising at least one acetic acid compound having the formula:

wherein each X is independently selected from the group consisting of hydrogen, hydroxyl and halogen and in which the acetic acid compound is present in a concentration sufficient to render the caprolactam substrate receptive to a noble metal catalyst.

4. A process as claimed in claim 3, in which the caprolactam substrate is formed of a filled caprolactam.

5. A process as claimed in claim 3, in which the total acetic acid compound concentration of the conditioning solution is from about 3 percent by weight of the solution to solution saturation.

6. A process as claimed in claim 3, in which the total acetic acid compound concentration of the conditioning solution is from about 5 to about 60 percent by weight of the solution.

7. A process as claimed in claim 3, in which the caprolactam substrate is contacted with the conditioning solution for a period of from about 10 seconds to about 1 5 minutes.

8. A process as claimed in claim 3, in which the acetic acid compound is trichloracetic acid.

9. A process as claimed in claim 3 in which the caprolactam substrate is contacted, prior to contact with the aqueous etch solution, with a dilute aqueous solution of an organic solvent for caprolactam for a time sufficient to soften the surface of the caprolactam substrate.

10. A process for etching the surface of caprolactam substrates for electroless plating which comprises contacting the caprolactam substrate with an aqueous etch solution of trichloracetic acid in which the trichloracetic acid is present in a concentration of from about 5 percent by weight to solution saturation for a time of from about 10 seconds to 1 5 minutes to render the caprolactam substrate receptive to a metal electroless plating catalyst.

11. A process as claimed in claim 10, in which the caprolactam substrate is formed of a filled caprolactam.

12. A process as claimed in claim 10, in which the concentration of trichloracetic acid in solution is from about 5 to about 60 percent by weight of the solution.

13. A process as claimed in claim 10 in which the caprolactam substrate is contacted, prior to contact with the aqueous etch solution, with a dilute aqueous solution of an organic solvent for caprolactam for a time sufficient to soften the surface of the caprolactam substrate.