Organic pre-etch treatment for metal plating of cyclic olefin polymers

#It is common in the process of metal plating plastics with copper, nickel, chrome or other metals to first chemically etch the surface of the plastic to form a microscopic texture on the surface that facilitates adhesion of the metal to the surface. This etching step is usually followed by the application of an activator such as a palladium-tin colloid, followed by electroless metal deposition. Such processes are described in Standards and Guidelines for Electroplated Plastics, published by the American Society of Electroplated Plastics; in Chapter 12 of Ni and Cr Plating by J. K. Dennis and T. E. Such (1972); in "Electroplating of Plastics in Theory and Practice" by Heymann, Riedel, and Woldt in Angew. Chem. Int. Ed., Vol. 9, (1970), pp 425-433; and in "Practical Formulations for Plating on ABS Plastics in Metal Finishing, March 1986, pp. 51-54, all of which are incorporated herein by reference.

#Alternatively, a "direct metallization" process can be used, which eliminates the electroless plating step. Such a process has been developed by Atotech and is called Futuron.RTM.. Here, too, it is known to chemically etch prior to the direct deposition of the metal.

#The surfaces of some plastics are more difficult to etch than others. Sometimes immersion of such plastics in a particular type of organic solvent prior to etching will make the plastic surface easier to etch and will sometimes improve the uniformity of the etching step. Generally it is believed that the organic solvent, where effective, causes the plastic to swell at the surface, thus creating or opening microscopic pores or fissures, thereby facilitating the acid's access to the plastic. The organic solvent can be used undiluted or in admixture with another liquid with which it is miscible, e.g., water. Such a step is often referred to as an organic pre-etch step. This pre-etch step has been reported in Ni and Cr Plating by Dennis and Such (1972, pg 289); Electroless Plating: Fundamentals & Applications (1990) Chapter 14, pg 382-383; Plating of Plastics: Recent Developments, Chemical Technology Review, No. 138, published by the Noyes Corporation in 1979; and U.S. Pat. Nos. 3,769,061, 3,445,350, 3,479,160, 3,963,590, 3,905,877, 3,898,126, and 3,758,332, all of which are incorporated herein by reference.

#A 4" by 4" by 0.15" thick specimen of RIM-molded Metton.RTM. LMR poly(dicyclopentadiene), molded with a cavity temperature of 90.degree. C. and core temperature of 60.degree. C., is immersed for 5 minutes in xylene held at room temperature (25.degree. C.) as an organic pre-etch. This is followed by immersion for 5 minutes in a 70.degree. C. aqueous etching bath containing 420 g/l of chromic acid and 325 g/l of sulfuric acid. The level of Cr.sup.3+ ion in the bath is about 7 oz./gallon. This is followed by sequential immersions in three rinsing baths of room temperature deionized water, then a neutralization step involving immersion for 5 minutes in a bath of 5% hydrochloric acid at room temperature, and then another rinsing in three sequential baths of room temperature deionized water. This is followed by immersion for 3 minutes at 40.degree. C. in deionized water containing Condiriser SP at a concentration of 150 ml/l. Condiriser SP is a cationic wetting agent sold by Okuno Chemical Company, of Japan. It serves to place a negative charge on the surface of the etched part, which promotes the attraction of the positively charged palladium ions during the treatment with the chemical activator, described next.

#Chemical activation of the etched part surface is accomplished by immersion for 5 minutes in a room temperature aqueous bath containing a palladium/tin hydrosol, Enplate Activator 850 (at a Pd/Sn concentration of 2%) and hydrochloric acid (at a concentration of 150 ml/l). This serves to deposit palladium ions on the etched surface. After several rinses in deionized water, the part is then immersed in a bath of dilute sulfuric acid at 40.degree. C. for 8 minutes. The bath contains about 100 ml of sulfuric acid per liter of water. This treatment serves to remove excess hydrolyzed tin hydroxide from the deposits of palladium on the part surface, so that the tin hydroxide will not inhibit the deposition there of the plating metal, in the next step.

#Finally, electroless deposition of nickel on the etched part surface is accomplished by immersion for 5 minutes in a nickel plating bath at 40.degree. C. The bath, having a pH of 8.5, is a 20 volume percent solution of Enplate.RTM.n Ni-429 in deionized water. Enplate Ni-429, like Enplate Activator 850, is sold by Enthone-OMI. Enplate Ni-429 is an alkaline, electroless nickel solution.