Fluoron’s Solution to “Static Buildup”
Static electricity has long been recognized as a serious workplace hazard, exposing employees to potential electric shock, fires, and explosions. While fluoropolymer covers can solve our “stickies” problem by lowering the surface energy of our process rollers, they often tend to create a new “static buildup” problem in rotating equipment, especially in dry areas of the machine. The willingness of a particular material to donate electrons is defined by the triboelectric effect. The further apart two materials are in the series; the more static electricity will build up when you rub them together.
If two materials are very close in the series, it’s hard to get them to build up any charge at all no matter how hard you rub them. As shown in Figure 7, rubber and fluoropolymers tend to gain electrons, while paper and other non-woven materials tend to give electrons. This is the reason that rubber or fluoropolymer covered process rollers often build up a charge in a manufacturing process where these materials are in repeated contact
What causes the static charge to build up and suddenly discharge as an electric shock?
The answer is found in how easily electrons move around within a particular material. In a conductor, electrons move freely throughout the entire body. Therefore, a charged conductor can be neutralized simply by connecting it to earth ground, since the ground is virtually an infinite source and receptacle for electrons. An insulator reacts much differently because electrons do not flow freely through the material.
In other words, the built-up charge is “static”, and the material cannot be neutralized by simply grounding it to earth. Because of this, an insulator retains the static charge on its surface until a discharge source presents itself and the electrons “jump” from one material to the other resulting in an electric arc. Figure 8 shows what happens when FEP sleeves are installed in a dry position where electrostatic arcing takes place and damages the sleeve.
Engineers have designed a way to eliminate this problem through the use of carbon fillers
In graphite, electrons which are not contained in the planar layer, are loosely bound and available for conduction of electricity. Therefore, carbon black addition to fluoropolymers is sufficient enough to cause a significant and abrupt increase in electrical conductivity. As the loading of the carbon black in the compound increases, the plastic compound remains initially insulating, as the loading increases, the conductivity passes through a sharp and abrupt rise over a very narrow black concentration (loading) range. Further increases in loading past this threshold cause little increase in the conductivity.
This narrow range is known as the percolation threshold shown in Figure 9. Specialty roll covers made from carbon filled PTFE enable the fluoropolymer to cross the percolation threshold which creates a conductive roll cover, eliminating the risk of static buildup and the risks associated with static discharge