Significantly reduced fluorination time needed for suppression of space charge in polyethylene by increasing the fluorination temperature

Polyethylene samples were surface fluorinated using a F-2/N-2 mixture under 0.1MPa at 35, 70 or 95 degrees C for different times. Space charge accumulation was found to show four basic types for each fluorination temperature with increasing fluorination time. But the fluorination times needed for the formation of the same type of charge accumulation are significantly different between the different temperature treatments. For example, the 60 min fluorination at 95 degrees C is sufficient to form the fourth type of charge accumulation (almost no space charge in the bulk), while this is not achieved even for the 360 min fluorination at 35 degrees C. Infrared analyses and scanning electron microscopy cross-section images of the fluorinated samples indicate the increases in the degree of fluorination and thickness of the fluorinated layer with fluorination time. These different types of charge accumulation arise from different blocking abilities between the fluorinated layers to both charge injection and extraction. The fluorinated layers formed at different temperatures with good blocking ability have almost the same high degree of fluorination and large thickness of about 0.70 mu m. This indicates that the increase in fluorination temperature has no negative influence on the electrical properties of the formed surface layer.