1. Field of the Invention
The invention relates to a process for reducing the residual hydrogen fluoride gases in a fluorinated plastic tank, in particular in a plastic tank for a motor vehicle, in which firstly the space within the tank is subjected to a fluorination step and then, in at least one gas flushing process, the reaction products of the fluorination step are removed from the plastic tank.
2. Description of Related Art
For fuel tanks, attention has recently been given to removing any possibility of fuel vapor escaping from the fuel tank into the environment. The escape of fuel vapor is disadvantageous for the user of the motor vehicle and also causes pollution.
Plastic fuel tanks are fluorinated on the inner side of the tank to achieve increased resistance to permeation of the fuel medium. This surface reaction with elemental fluorine gives hydrogen fluoride as an undesired reaction product.
The excess gas from the fluorine reaction and the hydrogen fluoride are therefore removed by suction after the process. The plastic tank is then additionally flushed with dry nitrogen or dry air in a gas flushing process to remove reaction products which have remained in the plastic tank.
Despite these measures, residual amounts of hydrogen fluoride remain in the tank, and this has an adverse effect on components subsequently incorporated into the tank, such as level indicators and feed units. Depending on how much residual hydrogen fluoride gas is still present in the atmosphere in the tank, the metal surfaces or the glassy surfaces of the level indicator and feed units become etched to some extent by the residual hydrogen fluoride. Incipient damage of this type causes premature failure of the potentiometers built into the level indicator and therefore of the entire level indicator.
The objective on which the invention is based is therefore to provide a process in which the undesired reaction product hydrogen fluoride is completely eliminated and which on examination is found to be suitable for large-scale production.