EXPLORING FOUR TYPES OF ANTI-STATIC AGENTS FOR CONDUCTIVE FLOORING
Comparison of strengths and weaknesses of the most commonly used anti-static agents: chopped or milled carbon fibers, antimony tin oxide and graphene nanotubes
Achieving the targeted uniform conductivity level in static dissipative flooring is heavily dependent on choosing the right anti-static additive. This article compares different types of anti-static agents that are frequently used to impart dissipative and conductive properties to epoxy and polyurethane self-leveling floorings: chopped or milled carbon fibers, graphene nanotubes and Antimony Tin Oxide (ATO).
For any anti-static agent, a conductive path can be formed within a resin once a particular dosage is reached. This is called the percolation threshold, and above it the electrical resistivity drops owing to the formation of an interconnecting conductive network. To simplify things, we will call the required amount of anti-static agent a “working dosage”, and for each anti-static additive we will define the so-called “price per property”.
CHOPPED AND MILLED CARBON FIBER
Carbon fiber is the most frequently applied anti-static agent for static dissipative flooring. Together, these two types of carbon fiber represent more than a half of the whole self-leveling anti-static flooring market share. They comprise 10–15 μm diameter carbon fibers based on coal tar pitch that are either chopped to a length of 2–6 mm or milled to a length of 0.13–2 mm. The working dosage for chopped carbon fiber is 1–2 wt.% while for milled carbon fiber it is 1–6 wt.%. Both of these carbon fiber options have a good price per property (0.2–1.5 $/kg) because of the relatively low initial fiber price and concentration required.
However, because of the length of chopped carbon fiber (2 mm or longer), the thickness of the top/base layer must be at least as much. This limitation results in increased costs, as the top/base layer accounts for almost 60% of the total cost to the customer. Anti-static flooring with chopped carbon fiber has a better appearance than flooring containing milled carbon fiber, but is more difficult and sensitive in terms of installation technology, and suffers from occurrence of insulating “hot spots”.
ANTIMONY TIN OXIDE
Conductive pigments, such as Antimony Tin Oxide, are usually supplied in powder form. Antimony Tin Oxide has the highest price per property at around 5–12 $/kg, which is a result of the high initial high price of the additive combined with the high working dosage required 8–20 wt.%. Antimony Tin Oxide has a negative affect on color of the floor the due to its high loading rate. Applying this anti-static pigment coating, applications are limited to 16 mils. Otherwise, if the coating is thicker, the ATO will settle leaving an insulative surface. And because most ATO systems incorporate the Antimony Tin Oxide as a part C, variations can appear from mix to mix, resulting in “hot spots” or “dead spots”.
GRAPHENE NANOTUBES
Graphene nanotubes (also known as single wall carbon nanotubes) are a relatively new product that is now being welcomed by the market. Their key advantage in comparison with traditional anti-static additives lies in the extremely low working dosage required to achieve the targeted level of conductivity – from as little as 0.01% of the total compound weight. Thanks to their small diameter and high aspect ratio, this minimal dosage of graphene nanotubes is sufficient to create a uniform conductive network. Extra-low working dosages open the door to reducing the thickness of the ESD coating (to go as low as 25 micron DFT) and to a full color palette. Graphene nanotubes help to significantly reduce installation and maintenance time, yielding additional cost savings.
Learn more about the performance of graphene nanotubes in ESD flooring. Explore TUBALL graphene nanotube concentrates, produced by OCSiAl, for anti-static epoxy and polyurethane flooring that make it easier to apply nanotubes in a standard manufacturing process.