Fluorocarbon polymers pretreatment

Simple abrasion is usually a very poor surface treatment for fluorocarbon polymers. This may be seen from the results shown in Table 4.2 where joint strengths for PTFE and PCTFE, bonded using an epoxy-polyamide adhesive, are given and the fluorocarbons have been pretreated by either abrasion or a... 

The treatment for fluorocarbon polymers is usually based upon metallic sodium dissolved in a solution of naphthalene in a polar aprotic solvent such as tetrahydrofuran, although other etch treatments such as a solution of alkali metal in liquid ammonia [12] have been reported [13]. Details for the preparation of the treatment solutions have been published [14] and solutions of sodium naphthalenide are commercially available, e.g. under the trade name Tetraetch from W. L. Gore Associates Inc. These commercial pretreatments are relatively easy and safe to operate and widely used in industry. Also, it is possible to purchase fluorocarbon polymers already treated by such chemical processes. 

Like the fluorocarbon polymers discussed above, polyolefins such as low- and high-density polyethylene, polypropylene and poly (4-methyl 1-pentene) cannot usually be joined by adhesives to give reproducible high strengths unless some form of surface pretreatment is first employed. 

As mentioned earlier, other plastics such as poly(vinyl chloride), poly (ethylene terephthalate), polyacetals, nylons and polyimides do not present such a severe problem to the adhesives technologist as do fluorocarbon polymers or polyolefins. Nevertheless, in order to obtain very high joint strengths approaching the cohesive strength of the substrate, some form of surface pretreatment is often necessary. 

Postdeposition plasma modifications to the plasma polymer of TMS have been seen to greatly improve bonding to various primers and paints [18-20]. One particular system has been observed to have tremendous adhesion between plasma-coated A1 alloy panels and paint applied to them. This system involves cathodic DC plasma deposition of a roughly 50-nm primary plasma polymer film from TMS onto a properly pretreated alloy substrate, followed by the deposition of an extremely thin fluorocarbon film by DC cathodic deposition of hexafluoroethane (HFE). It was the superadhesion aspect of this particular system that triggered the series of ESR studies [3,21]. 

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