Not everybody can sit at a bench with a wriststrap on. Some workers and materials must move around. So what do you do? Maybe it’s time to consider ESD-control flooring or floor coatings that can reduce the voltage buildup on people and material-handling carts.
The Selection Process
Whether it’s for an office, a clean room, or a warehouse, there’s an ESD-control flooring or coating that will do the job. But, the selection criteria is very different for each one.
An office, for example, typically is a place where the traffic isn’t heavy, chemical spills aren’t likely, and appearance and noise suppression are important. Carpet tiles could be best for this environment.
At the other extreme is a warehouse where forklifts are used to move material. You want a floor that’s durable, seamless, and easy to clean and resists moisture, abrasion, and chemicals. A permanent epoxy floor is worth considering. This polymer provides consistent and enduring electrical performance, according to Karl Sauereisen, marketing manager at Sauereisen. Naturally, he said, customers are concerned about the aesthetics or method of application, but mostly they need the benefits of permanent and consistent conductivity.
Customers also are interested in epoxy flooring because they want durability to withstand extremely heavy industrial traffic such as forklifts, superior chemical resistance, and low maintenance costs, pointed out Steve Koehn, senior technical service and applications engineer at 3M. Epoxy creates a seamless floor, he said, so it doesn’t need special care.
In a clean-room environment, other properties become important. The traffic isn’t as heavy as in a warehouse, so a vinyl floor might be appropriate. The seamless type is preferred to prevent trapping dirt. You may want to avoid products containing carbon, which is a source of contamination, or materials that outgas, such as volatile organic compounds.
For more general applications such as a production floor, vinyl tiles may work well. Vinyl tile, indicated Mr. Koehn, can have some of the lowest installation and maintenance costs of any ESD-control flooring product.
Floor Coatings
If a permanent floor isn’t in the offing, there are coatings which may be applied over an existing floor. Some product manufacturers indicate that to get the desired results floor preparation is required prior to coating. Follow the application instructions exactly, because you may not be able to remove the coating later if necessary.
Some coatings require reapplication at regular intervals to maintain the ESD properties of the floor. This may not be suitable in areas where a lot of dirt, high abrasion, chemical spillage, or heavy traffic exists. You could encounter high maintenance costs and may even find it necessary to interrupt the workflow occasionally to maintain the floor.
Coatings are not a capital expense, and aside from floor preparation, little installation work is required. Jeff Bauer, technical manager at Walter Legge, pointed out that customers want long-term results from coatings as well as a diverse color spectrum to choose from.
Floor Care
To help keep your flooring or coating at optimum effectiveness, most manufacturers will provide maintenance guidelines. Simply follow the written instructions to keep the flooring surface clean, indicated Steve Parker, national product manager-ESD at United Technical Products (UTP).
The initial expense of permanent flooring sometimes can be offset because of low periodic maintenance costs. An epoxy floor is a high-performance product with permanent and consistent electrical properties. It is durable and seamless and resists chemicals and abrasions. Maintaining this type of floor is as simple as keeping it clean, said Mr. Sauereisen. A wet mop or floor cleaner usually is suitable, but avoid depositing a film or residue on the surface.
Many vinyl floors only require damp-mopping. Tile floors are easy to install, but they are more likely to trap dirt than a seamless floor. As you would expect, a carpet is maintained very differently, requiring regular vacuuming, scheduled professional cleaning, and occasional spot cleaning.
There are floor mats you can place in entrance ways to trap dirt. This prevents tracking heavy soil into the work area, according to 3M’s Mr. Koehn. He said that the rest of the cleaning job can be done by damp-mopping light dirt and spills.
If the flooring or coating does not come with a complete maintenance program, said Mr. Bauer of Walter Legge, you are compromising the ESD effectiveness of the surface. Details are important. To ensure that you apply the proper concentration of cleaning solutions, for example, he recommended that you use automatic dispensing equipment.
The maintenance goal of an ESD-control floor is to clean the surface without attacking it chemically, altering its resistance, or leaving a residue. You may want to avoid cleaners with zinc, phosphates, or other environmentally unsafe products. Also, if the pH is below 4 or above 11, a solution may chemically attack the floor surface. Ammonia, for example, has a high stripping action.
Controlling ESD
Controlling ESD is twofold. One method is to prevent the charging
process, and the other is to provide a safe discharge. Materials used to prevent charging are called antistatic, and those used to safely discharge are static dissipative.
To prevent voltage buildup on a person walking across a floor, the triboelectric effect must be taken into account. This is because two different materials can charge when there is friction between them. One way to prevent this kind of charging is to make floors and shoe soles out of similar materials.
For safe discharge, the ESD Association recommends keeping an object’s resistance to ground between 106 W and 109 W . For a human, this is the sum of the resistance to ground of the shoes plus the surface resistance to ground of the floor. Both shoes and flooring are available with a resistance-to-ground range of 106 W to 108 W .
The sum of these two resistances will be between 2 × 106 W and 2 × 108 W which is within the ESD Association’s recommendation. You can make these point-to-point measurements with a simple megohmmeter or a wrist-strap checker.
The floor’s resistance to ground is more important than its surface resistivity. Resistivity is a measure of how a charge will dissipate on the surface, but it is voltage on a person that does the damage and must be prevented or safely discharged.
According to Mr. Parker of UTP, customers are interested in the point-to-point and point-to-ground resistance of the floor surface. They want to be sure that these measurements are accurate, repeatable, and reproducible. He said they also are concerned with the triboelectric properties of various flooring materials.
Most wheels and shoe heels are made of rubber, which is insulative, and this allows a charge to build up on people, carts, and forklifts. To discharge vehicles and their contents, conductive strips sometimes are connected to the metal frame and allowed to drag on the floor. Since forklifts back up a lot, this may prove impractical without resorting to a special design.
Flooring-Related Standards
Learn all you can about ESD standards for flooring and floor coatings.
ESD ADV-2.0-1994 is an overall guide to ESD control. ANSI/ESD 7.1-1994 covers the resistive characterization of floor materials, and ESD S9.1-1995 describes footwear resistive characterization. ESD DSTM54.1-1997 and ESD DSTM54.2-1997 outline how to measure the resistance of, or voltage on, a human due to the relationship between floor materials and footwear.
Floors/Floor Coatings
Dissipative Tile Has
The 8400 Series Vinyl Tile contains sealed carbon and provides permanent dissipative properties without wax or polish. Available in 12 colors, the 1/8″-thick tiles are edged for squareness and seam-weldable for clean rooms. The standard size is 12″ × 12″, with optional sizes of 24″ × 24″ and 36″ × 36″. The surface resistance to ground, per ESD S7.1, is 106 W to 109 W or 2.5 × 104 W to 106 W . Static generation measures less than 50 V at 20% relative humidity with conductive footwear. 3M Electronic Handling Protection Division, (800) 328-1368.
Cleaner Maintains
Conductive Vinyl Tile
Statshine is a concentrated cleaner that creates a barrier between the dirt and the floor. It cleans, shines, and decreases triboelectric charges and will not change the resistance of the existing surface. Statshine may be used daily because it will not build up on the surface. The cleaner can be dry buffed to a high shine if desirable. Walter G. Legge, (914) 737-5040.
Rubber Flooring Generates
Less Than 20-V Static Charge
Noraplan Stone AL is a static-dissipative rubber floor covering that resists most oils, greases, chemicals, and hot solder. It generates less than 20 V of static charge and is free of carbon, PVCs, asbestos, and halogens. This slip-resistant covering does not need waxing. Nondirectional patterns, sprinkled patterns, and 3-D cluster designs are provided in 18 colors, including white/blue and white/beige. Freudenberg Building Systems, (800) 332-6672.
Epoxy Topcoat
Resists Chemicals
ConductCoat No. 2383, a seamless epoxy floor coating, is the top layer of the company’s three-part flooring system. The 20-mil thick coating resists chemicals and provides flooring for moderate traffic due to high compressive, flexural, and tensile strength. The coating is available in 106 W to 109 W and 2.5 × 104 W to 109 W resistance ranges and beige, tan, light gray, and dark gray colors. Sauereisen, (412) 963-0303.
Epoxy Flooring Limits
Static Charge to 25 V
Stonlux AT, a seamless three-part epoxy flooring system, can be applied in an 80- or a 120-mil thickness. It comes in 106 W to 109 W , and 2.5 × 104 W to 106 W resistance ranges. The maximum voltage generated by a person wearing conductive footwear is 25 V at 25% relative humidity. Available in standard and custom colors, the high-strength surface is smooth and easy to clean and resists abrasions and chemicals. Stonhard, (800) 257-7953.
High-Gloss Finish Resists
Wear, Dissipates Static
Statguard® Floor Finish dissipates static charge, prevents triboelectric generation, and provides a clear, high-gloss finish that resists wear. The liquid emulsion is applied to hard surfaces of sealed flooring, including vinyl, vinyl asbestos, linoleum, rubber, asphalt, sealed or painted wood, terrazzo, and concrete. It can be used in clean rooms and electronic manufacturing, assembly, and test areas with a relative humidity from 30% to 65%. Charleswater, (781) 821-8370.
Vinyl Tile Has
Low Outgassing
Conductile XLE® Vinyl Tile limits static-voltage generation to <50 V at 20% relative humidity with conductive footwear. It provides a 98% reduction in outgassing when compared to DOP- or phthalate ester-containing products. The tile has 2.5 × 104 W to 106 W point-to-point resistance and less than 2.5 × 104 W point-to-ground resistance. The standard size is 24″ × 24″; custom sizes are available. VPI, (920) 458-4664.Carpet Tile
Absorbs Noise
CompuTile ESD Carpet Tile has a point-to-ground resistance of 105 W to 108 W . The point-to-point resistance, measured at a 1-ft spacing and an applied voltage of 100 V, is 2.5 × 104 W to 5.0 × 106 W . This carpet tile limits human body voltage to 15 V at 20% relative humidity with conductive shoes per AATCC-134 step test. It absorbs 10 times the noise of a hard surface floor. The standard tile size is 18″ × 18″ with a pile height of 90- to 125-mils. United Technical Products, (800) 225-6052.
Floor Coating Limits
Body Voltage to 15 V
The Chemi-Cote® ESD EP-1000 Epoxy Floor Coating can be applied to all surfaces, including floors, walls, and ceilings. The three-piece kit consists of the basic material, an activator, and a color pack. The smooth, nonporous coating resists impacts, abrasions, and chemicals. Body-voltage generation is limited to <15 V, and the surface is easy to clean and comes in several colors. Two resistance ranges are featured: 2.5 × 104W to 106W and 106W to 109 W . This coating contains 96% solids and has low volatile-organic content. Garland Floor, (800) 321-2395.Floor Finish Has Water
Base, Stays Conductive
URE-STAT is a water-based urethane floor finish. Its’ static-dissipative resistivity range is 107 to 109 W /sq for two coats. Virtually unaffected by water, the finish is easy to maintain on a daily basis with the company’s cleaners without adversely affecting the readings. The static decay time is 0.07 s, from 5 kV to 0 kV according to MIL-B-81705B. Walter G. Legge, (800) 345-3443.
Copyright 1999 Nelson Publishing Inc.
February 1999