Flame-treating process

Abstract

The present invention provides a method of modifying the surface of a polymeric substrate, e.g., to improve the wettability of the polymer film surface and/or alter the reactivity of the surface of the substrate by further oxidation or affixation of nitrogen, comprising exposing the substrate to a flame. The flame is supported by a fuel and oxidizer mixture that includes an effective amount, for modifying the polymeric substrate, of at least one compound that functions as a fuel or oxidizer substitute and is selected from an oxygen-containing compound, in which the oxygen comprises between about 10 and 50 atomic percent of the compound, a nitrogen-containing compound or an oxygen-nitrogen-containing compound. In a preferred embodiment, which affixes nitrogen or nitrogen-containing chemical groups onto the surface of the film, the flame is supported by a fuel and oxidizer mixture that includes ammonia, nitrous oxide, nitric oxide or a mixture thereof in an effective amount. Large increases in the ASTM wetting test, e.g., greater than 13 mJ/m.sup.2 over that reported with conventional flame-treating processes, have been observed in films treated according to this invention. In addition, significant increases in polymer film surface oxidation levels, e.g., as much as 55 percent, have been observed, as have significant amounts of nitrogen and nitrogen-containing chemical groups affixed to film surfaces.