Fluorination of Plastic Fuel Tanks

Polyethylene, the plastic employed for the production of fuel tanks, has the disadvantage of being relatively permeable to fuel; this undesirable property leads to leakage to the extent of about 20 g per day from an average fuel tank.

The automobile industry today accepts a leakage of around 2 g per day, but is striving to attain a maximum level of 0.2 g per day as the standard for the future. Such a figure is achievable through the process of direct fluorination. The permeation of fuel through polyethylene fuel-container walls can be dramatically reduced by the chemical process of forming a layer which is almost impermeable.

Comparison:
Permeation in Plastic Fuel Tanks

Finishing of Plastic Surfaces

The direct surface-fluorination of polyethylene components also results in a reduction in the permeation rates of gases such as oxygen, nitrogen, carbon dioxide, sulphur dioxide, C2H2 and halogenated hydrocarbons. The permeability rate of oxygen through treated PE pipes is reduced to less than 0.5% of the original value.

 


At the same time both the thermal stability and the chemical resistance to acids and alkalis are improved. Fluorinated PE-sheets exhibit a lowered coefficient of friction and acceptance of printing-inks is improved. The finishing of plastic surfaces by direct fluorination is not, however, limited to polyethylenes. Basically, any kind of plastic or rubber can be fluorinated.

The finishing of plastic surfaces is of great significance in the foil industry. For the production processes of glueing, coating, laminating, painting and printing good adhesion is absolutely essential.

During the nineteen eighties a continuous fluorinating process was developed for the treatment of foils. In this method the surfaces of foils can be activated, on one or both sides, independent of the size and length of the rolls, in a continuous process from roll to roll. The fluorination of almost all types of foils consistently results in a significant increase in surface energy.