The invention pertains to a coating for application to a substrate, whereby the coating comprises at least one the thermoplastic fluorine-containing polymer, and its hardness decreases from the first surface, which is destined for application to the substrate, in the direction of the second surface which is remote from the substrate. The hardness gradient can be achieved by adding filling or reinforcing agents or by addition of at least one thermoplastic polymer. The invention additionally pertains to a gasket that consists of the coating in accordance with the invention or that comprises it.
A method for reducing fuel permeation through gasketed joints in an internal combustion engine (10) includes surface treating the gaskets in a halogenated medium before placing them into service. A low-cost elastomer such as acrylic, EPDM or HNBR, can be used for the gasket body. The halogenated medium may comprise either a liquid bath or a gaseous bath, into which the gasket is immersed. The halogenated medium bath is excited by heating to accelerate the halogenation process. A gasket treated according to this invention possesses a chemically altered exterior surface which substantially enhances its fuel permeability resistance at relatively low cost.
