Metal Plated or Platable Article

Many metals can be deposited autocatalytically from baths which include a salt of the metal, a suitable reducing agent, a chelating or complexing agent and a pH-adjusting agent. The surface being plated must either be inherently catalytic for the autocatalytic deposition process, or it must be treated to render it catalytic. Glass and synthetic resins, for example, are not inherently catalytic. Usually, these and other non-catalytic surfaces can be rendered catalytic by, first, treating them with a sensitizing agent such as stannous chloride and then treating them with an activating agent such as palladium chloride. The stannous chloride treatment deposits a film of stannous ions on the surface and the stannous ions reduce some of the palladium salt to palladium. The metal being plated out builds up around palladium nuclei.

Although glass and most resins are readily wetted by solutions of the sensitizing agent and the activating agent, some plastics, such as polytetrafluoroethylene (Teflon), are so hydrophobic in nature that wetting is very non-uniform. This type of surface is difficult to plate autocatalytically. Also, many plastics which are not hydrophobic, still are difficult to plate with an adherent metal coating because they present a highly smooth surface to the metal film being deposited. For this reason, when the article being made requires that the metal coating be strongly adherent, as in making printed circuit boards, for example, the surface being plated must first be roughened to increase its porosity.

One aspect of the present invention is an improved article which may be plated autocatalytically. The article comprises any substrate, whether or not it is normally difficult to plate electrolessly, having on a surface which it is desired to plate, a film of a resin having incorporated therein a hydrolyzed metal complex. The hydrolyzed metal complex has adsorbed thereon a metal which is a catalyst for autocatalytic deposition of the metal being plated. The usual stannous chloride sensitizing treatment is not required. Another aspect of the invention comprises the above described article with a coating of metal deposited thereon.

An example of a substrate which is normally difficult to plate electrolessly is a body made of polytetrafluorethylene (Teflon) resin. To prepare this body for electroless metal deposition, the body is coated as follows.

A solution of an alkyl ortho titanate is prepared by dissolving 5% by volume of tetrakis 2-ethyl hexyl ortho titanate (Tyzor TOT, made and marketed by E. I. du Pont de Nemours and Co.), in Freon TF (E. I. du Pont de Nemours and Co.). To 150 cc of this solution is added 2 cc of a solution of an Indopol resin (Polybutene), (Amoco H-1900), which is prepared by dissolving 200 g of the resin in 250 g of Freon TF.

The resin solution is applied to the Teflon surface and the Freon TF is allowed to evaporate. The surface, which is now coated with the dried film, is dipped in a 0.1 molar NaOH solution for 30 seconds; this hydrolyzes the titanium compound to a titanium composition believed to comprise a complex mixture of oxides and hydroxides. The hydrolysis can also be carried out by treating the dried film in steam for 1 minute. After the hydrolysis treatment, the surface is rinsed in deionized water.

A metal which is catalytic to the electroless deposition of another metal which it is desired to plate out on the resin film is then adsorbed on the hydrolyzed titanium complex. For example, the surface may be treated with a dilute acidic solution of PdCl.sub.2 to adsorb palladium ions. The palladium solution comprises 1 gram of PdCl.sub.2 and 1 cc of concentrated HCl in a liter of water. This is followed by rinsing with deionized water to remove excess palladium ions.

Nickel may then be plated on the surface by immersing it in an aqueous solution having a composition as follows:

This bath is operated at room temperature.

The amine borane is a strong enough reducing agent to reduce the palladium ion to palladium metal and cause nickel deposition without any pre-treatment to convert the palladium ion to metallic palladium. However, if a conventional nickel-phosphorus bath in which the reducing agent is sodium hypophosphite is used to deposit the nickel, the surface must first be treated with a reducing agent to effect the ion-to-metal conversion. The pre-reduction can be carried out by treating the surface with formaldehyde, for example, or dipping the surface in the above nickel-boron bath.

A polypropylene resin substrate is first coated with a high molecular weight resin (Vistanex LM-MS, Humble Oil Co.) film containing an alkyl ortho titanate. A solution of the resin is prepared by dissolving 120 g of the resin in 200 g of Freon TF and 2 cc of this solution is dissolved in 150 cc of a 1% by volume solution of Tyzor TOT in Freon TF. The solution is applied to the substrate and the solvent is permitted to evaporate to form a solid film.

Palladium ion is caused to be adsorbed on the dried film by treating the film with a solution of palladium chloride as in Example 1 and, after rinsing, nickel may then be electrolessly deposited on the surface without pre-reduction of the palladium ion using the nickel-boron bath of Example 1.

Copper can also be electrolessly deposited on the activated surface without pre-reduction of the palladium ion using the following aqueous bath.

This bath operates at room temperature.

Nickel-phosphorus alloys can be electrolessly deposited on the surface of the film if the palladium ion is first reduced to palladium metal. The reduction can be carried out by treating the surface of the film with a reducing agent such as an amine borane or formaldehyde.

In this example the PDTANa.sub.4 is a chelating agent.

Silver ion instead of palladium ion may be adsorbed on the resin films of either of the preceding examples or of any of the following examples, to serve as the activator or catalyst for electroless deposition. This is done by treating the resin film with a 0.1N solution of silver nitrate. The surface is then rinsed to remove excess silver nitrate solution. Without pre-reduction of the silver ion to silver metal, nickel can be electrolessly deposited on the catalytic surface using a nickel-boron bath as in Example 1 or a copper bath as in Example 2.

Instead of the tetrakis 2-ethyl hexyl ortho titanate of the previous examples, tetra butyl ortho titanate (partially polymerized) (Tyzor PB) is used as the hydrolyzable material. A solution is prepared which may comprise, for example,

This solution is used to deposit films on Teflon and Cronar (a polyester resin made and marketed by E. I. du Pont de Nemours) substrates and the resin film is activated either with silver nitrate or palladium chloride after hydrolysis of the Tyzor PB. Nickel or copper can be electrolessly deposited on the activated film as described above.

A resin film may be deposited on both Cronar and *Acrylite resin substrates from the following solution:

The Tyzor PB is hydrolyzed in steam, and silver ion is then adsorbed on the film from a silver nitrate solution. Nickel or copper may then be electrolessly deposited on the activated film as described above or by using other conventional nickel or copper plating baths.

A resin film may be deposited on Teflon or Acrylite, for example, from the following solution which contains a different solvent from the previous examples.

Films deposited from this solution, hydrolyzed in steam and then treated with palladium chloride or silver nitrate may be electrolessly plated with nickel or copper as in the previous examples.

A resin film containing hydrolyzable titanium may be deposited on a substrate composed of either Cronar resin, polypropylene resin or Acrylite resin from a solution comprising:

The Tyzor PB is hydrolyzed in steam as in previous examples and the resin film may have silver ion or palladium ion adsorbed thereon. The activated film may have nickel or copper electrolessly deposited thereon.

The hydrolyzable substance can be something other than an alkyl ortho titanate. It can be TiCl.sub.4 which is also hydrolyzable to form an oxide-hydroxide complex. In this example a solution of TiCl.sub.4 may comprise:

This solution may be used in a resin film deposited from another solution such as the following:

The resin film may be deposited on substrates such as Teflon, polypropylene and Acrylite. The TiCl.sub.4 is then hydrolyzed with steam as was the Tyzor PB or TOT of previous examples. After the hyrolysis treatment, silver ion or palladium ion may be adsorbed on the film which may then be electrolessly plated with nickel or copper.

A resin film may be deposited on any substrate using the following composition:

After hydrolysis of the titanium compound with steam and adsorption of silver ion or palladium ion on the film, copper or nickel may be electrolessly deposited on the film as previously described.

The hydrolyzable substance may also be AlCl.sub.3. A stock solution suitable for use in the present method is as follows:

The solution may be diluted 10 to 1 with Freon TF when used. Any of various synthetic resins may be used as the film binder. One example is 3 ml of a 50% by wt. solution of polybutene resin in Freon TF, in 100 ml of the above solution. When the film produced from this composition is hydrolyzed and activated with palladium or silver, copper or nickel can be electrolessly deposited thereon.

In general, the present metal deposition process includes depositing a resin film on the object to be coated where the resin film contains a substance that is hydrolyzable to form an oxide-hydroxide complex. The resin serves as a matrix or binder and adherence agent. The film is deposited from a solution containing a volatile solvent which is capable of wetting the surface of the object being plated. The volatile solvent is evaporated. The process also includes hydrolyzing the hydrolyzable substance, rinsing and then adsorbing on the film, a metal which, when is reduced metal form, is capable of serving as a catalyst for the autocatalytic deposition of the desired metal. The desired metal is then deposited on the activated film using any conventional electroless plating bath. If the bath does not contain one of the stronger reducing agents such as an amine borane or formaldehyde, the adsorbed metal ion must be reduced to metal before treating with the electroless plating solution.

Although alkyl ortho titanates are preferred hydrolyzable substances to use in the present process, other hydrolyzable metal compounds such as titanium tetrachloride, zirconium tetrachloride and aluminum trichloride are also suitable. The hydrolyzable material must be soluble in the volatile solvent that is used. This may be accomplished by forming soluble complexes of the above as for example the AlCl.sub.3 -ether complex, noted above.