Kravchenko Vladimir, Project Manager, OCSiAl Group, Luxembourg
Electrostatic discharge (ESD) is an ongoing problem for the electronics industry. The cost of static faults to the lectronics industry is estimated to be tens of billions of
U.S. dollars annually. Furthermore, ESD is not only a significant
cause of device failure, it also impacts productivity, product reliability, manufacturing profitability, and personnel safety in a
number of fields, including petroleum and chemical processing,
munitions plants, textiles, clean rooms, and hospitals.1 One ESD
prevention measure that appears to be effective is the installation of static control flooring.
Achieving the targeted uniform conductivity level in static
control flooring is dependent on choosing the right conductive
additive. For imparting dissipative and conductive properties
into epoxy, PU and PVC flooring compounds, manufacturers
introduce carbon black, carbon fiber, metallic fibers, mica particles or polymeric anti-static agents into the resin structure.
However, the majority of the commonly used conductive additives require a high loading level, starting at 3% and going as
high as 20%, which inevitably leads to difficulties in processing
and also negatively impacts color (Table 1).
High loadings of the conductive additive can decrease the mechanical strength of floorings and degrade the surface smoothness. Furthermore, many conductive additives have problems
with achieving uniform dispersion in the compound matrix, so
manufacturers often have to deal with the widespread occurrence of hot spots on the surface.
The additive that is capable of solving the loading level
problem and the associated negative effects was discovered
25 years ago – single wall carbon nanotubes. With more than
a decade of research and a number of breakthroughs in recent
years, viable commercial-scale solutions have now emerged
to integrate these nanotubes into industrial products, including batteries, plastics, elastomers, coatings, and resins.
ESD flooring has been a notable success story with flooring
products containing single wall carbon nanotube additives
already in production.
Single Wall Carbon Nanotube Properties
For any conductive additive, a conductive path can be formed
in a resin once a particular dosage is reached. This is called the
percolation threshold and above it the electrical resistivity drops
due to the formation of an interconnecting conductive network.
The key advantage of single wall carbon nanotubes compared
to other traditional additives lies in the extremely low dosages
required to reach the targeted level of conductivity – from as
little as 0.01% of total compound weight. Due to their small diameter and high aspect ratio, this minimal dosage of nanotubes
is sufficient to create a uniform conductive network in the material matrix2 that provides a compound with a surface-to-surface
and surface-to-ground resistance level in the range of 108 – 10²
Ω•cm in compliance with the following worldwide standards:
ANSI/ESD S 2020, ASTM F 150, IEC 61340-5-1, NFPA 99, and
SJ/T 11294-2003.
Figure 1 shows the volume resistivity in two different resin
systems at various loadings of the single wall carbon nanotubes.
The resin systems were an epoxy (D.E.R. 330) and a polyester
Fundamental Improvement in ESD Flooring with 0.01% Additive.
Single Wall
Carbon Nanotubes
Table 1. Comparison of the required loading levels of various conductive additives.
