“Epoxy floor” is a generic term for a floor coating system. There are different ways to produce these coatings and technologies have changed over the years. Early epoxy coatings consisted of resins loaded with high concentrations of carbon or graphite, and came only in black. These coatings performed well in ESD tests but were unattractive.
Generation 2 coatings consist of an insulative primer, conductive ground plane, and shiny top coat with some conductive fibers.
Generation 2 epoxies look great and come in a variety of colors but do not always pass body voltage tests required by ANSI S20.20.
Manufactured on the job, these floors are difficult to install with a high risk of flooring failures. Generation 3 coatings consist of an insulative primer and glossy, fully conductive, colorized top coat. Nanotechnology permits full infusion of conductive particles, for an attractive system that passes all ESD tests.
In the industrial world, the phrase, “epoxy floor,” is often used when some kind of Part A and Part B polymer – or resinous – floor coating system is mentioned. Resinous floor coatings encompass a number of different polymer technologies, including but not limited to epoxies, urethanes, polyaspartics, methyl methacrylates (MMA), and vinyl esters. In generic conversation all of these materials get lumped together under the heading “epoxy floor.”
Over the years, epoxy floors for ESD control have evolved significantly in both performance, durability and aesthetics. The first ESD coatings (Generation 1) were resins loaded with high concentrations of carbon or graphite. Just like the first Ford cars, you could have any color floor – as long as you liked black.
These floors performed extremely well in static-control performance tests. However, carbon-colored generation 1 floors were viewed unfavorably due to their appearance. These floors were usually installed in munitions and explosives handling applications.
Designers of the next generation (Generation 2) ESD coatings addressed the need for color options by introducing a multi-layer installation process whereby a semi-conductive top coat was installed over a much more conductive middle layer ground-plane.
Generation 2 technology relied on the concept of path of least resistance by utilizing two parallel conductors. As with Generation 1 technology, the black primer layer was overloaded with carbon black or graphite. To address the need for color options, the top layer was produced with less carbon or less fiber, allowing colorization. Essentially, just enough conductive additive is/was used to provide a leakage path from the top layer into the buried ground-plane below. This enabled the opportunity to build floors that came in a full array of color options.
Designed and installed properly, Generation 2 floors provide electrical resistive properties in both the conductive and static dissipative range. Generation 2 technology was the prevailing technology for at least 25 years. This technology, however, contains a hidden pitfall.
Until 2014, ESD flooring qualification and compliance audits consisted of simple resistance testing using a megohm meter. These resistance tests were performed using test method ANSI/ESD S7.1. As long as the floor measured below 1 billion ohms (10E9) and the aggregate resistance (per ANSI/ESD 97.1) of the Person + ESD footwear + ESD Floor = < 3.5 x 10E7 the floor was considered ANSI compliant and the personnel grounding met all pertinent ESD standards requirements.
Generation 2 epoxy floors usually passed S7.1 and S97.2 tests but not always. Forensics usually determined that the cause of an epoxy failing to meet 7.1 and 97.2 testing was either uneven distribution of conductive particles in the top coat and or inconsistent thickness of the top coat. In some failures the root cause was determined to be the result of a reapplication of the top coat over previously applied top coat. Too much thickness prevents electrical current from reaching through the top coat into the highly conductive buried ground-plane.
Buried layer ground-plane floors generate unacceptable static charges on people despite appearing to provide adequate conductivity. This problem is called tribocharging.
These problems revealed a previously undiscovered greater cause for concern: Buried layer ground-plane floors generate unacceptable static charges on people despite appearing to provide adequate conductivity. This problem is called tribocharging.
The main focus of ANSI/ESD S20.20 is to design an ESD program that prevents body voltage generation above 100 volts in the ESD-protected area. To expose body voltage generation aka tribocharging problems, the ESD Association added new requirements for the qualification phase of selecting ESD flooring. The changes were driven by the need to address body voltage on a person wearing ESD-controlled footwear.
In the years leading up to the 2014 revision of ANSI/ESD S20.20-2014, ESD auditors had encountered numerous flooring installations where the flooring measured in the conductive range and yet it did not limit static charges on people below the ANSI 100-volt limit. In the majority of lab tests, Generation 2 epoxy floors allowed charges of 300 to 700 volts on people walking while wearing properly functioning heel straps.
The new version of S20.20 requires qualifying a floor in a test lab at 12% relative humidity (ANSI/ESD S97.2) and proving that the floor will not allow a charge over 100 volts on any person wearing the exact footwear that will be used in the facility. Due to the semi-conductive top coat, Generation 2 epoxy floors do not address this requirement adequately. In most cases they fail, in part due to lack of surface conductivity.
There are multiple reasons why Generation 2 epoxies don’t fare well in 97.2 body- voltage tests. The most basic explanation is that these designs utilize top coats that are comprised almost entirely of standard, high-static-generating resins. There is just enough conductivity in these top coats to leak the charge to the buried, highly conductive ground- plane – but an inadequate amount of conductivity to minimize charge generation.
Given that the highest percentage of the top coat is made of standard, static-generating epoxy, the Generation 2 top coat is the weak link in the chain. If this were not the case, these systems would not require the application of a buried ground-plane. This translates to a scenario where a person is actually walking on a material that either strips or offers up electrons to their shoe sole as their feet contact and separate from the top coat.
The result: significant tribocharging.
As previously discussed, Generation 2 floors were initially designed to address the market desire for light color options. Since this desire was addressed by isolating (hiding) the most conductive element in the system, the solution added variables – i.e., a less conductive layer on top that required field application at a precise thickness.
Both layers were unnecessary for actual electrical performance and the process created a quality control dilemma on every Gen 2 job site. Because the conductive top layer required field application, the job site became not only the location where the floor was to be installed; it also became the materials manufacturing site of the floor (adding yet more variables).
It is extremely difficult to precisely control the exact thickness of a top coat when you’re installing in large, acre-plus sized facilities with changing environmental conditions and varying concrete textures on every job. The only way to cope with these real-world incompatible variables was to expect perfect design, perfect execution, and a lot of luck.
There are numerous examples in design history of product and system failures due to poorly envisioned statistical possibilities when too many variables are present in the same product.
New additive technologies enable us to produce fully conductive colorized top coats (colored and clear). This translates into a floor that requires a standard concrete primer, one layer of top coat and no conductive primer layer. The biggest benefit of the solution: The conductivity is on the surface and the conductivity is no longer thickness dependent. In other words, we have eliminated the two main variables that contribute to performance failure.
Because the conductivity is at the surface, we can provide a coating with extremely low tribocharging properties with any ESD footwear at any humidity level. A thinner top coat provides the added benefit of being less vulnerable to blistering and vapor problems from high RH concrete. In most cases Generation 3 floors can be installed at ASTM 2170 RH numbers as high as 95%. This enables installations over relatively new concrete.
In the event a Generation 3 floor requires a repair in an area that was heavily abused by frequent dragging of wooden pallets with protruding nails, a new top coat can be applied directly over the existing floor. The new surface will become the new path to ground. Generation 3 coatings can be applied directly over old coatings after sanding. This is impossible with old technology Gen 2 conductive ground-plane-reliant coatings.
|ESD COATINGS||GENERATION 1||GENERATION 2||GENERATION 3 |
|GENERATION 3 |
|Electrical resistance can |
measure in the conductive
or dissipative range
|Available as a conductive or |
|Does not require a |
conductive ground plane
|Available in light colours||❌||✔||✔||❌|
|Meets ANSI/ESD S20.20 |
with foot straps
|Can be applied over existing |
flooring in a single coat
|Glossy finish without |
application of ESD polish
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The FAA has updated its standard for facilities and electronic equipment. StaticWorx meets all requirements for ESD flooring.
Unless otherwise stated, standards referenced are the most up-to-date versions.