Process for the production of permeation resistant containers

In a process for the production of a blow molded, permeation resistant thermoplastic article via in-line fluorination wherein a parison of thermoplastic material is formed, expanded within a closed mold by means of an inflation gas for conforming the parison to the shape of the mold and fluorinated at a temperature above its self-supporting temperature under conditions sufficient to effect surface fluorination of the interior of said parison thereby reducing its permeability to hydrocarbon fuels and thereby forming the blow molded, permeation resistant article, the article is then evacuated and recovered, the improvement comprising the steps of:

• effecting an initial fluorination by pressurizing the parison while at a temperature above its self-supporting temperature with a reactive fluorine containing gas containing from about 0.1 to 1% fluorine by volume for a time sufficient to effect fluorination of the interior surface of the parison and thereby form a pre-fluorinated parison;
• and then,
• subsequently pressurizing the interior surface of the pre-fluorinated parison for effecting secondary fluorination by contacting the interior surface with a reactive fluorine containing gas having a fluorine concentration of at least twice that employed in the initial fluorination but not less than about 1% fluorine by volume, said parison being at an elevated temperature but below the self-supporting temperature during at least part of the secondary fluorination.