Methods and Technical Standards for Testing Epoxy Anti-Static Flooring and Precautions

Epoxy anti-static floor detection methods and technical standards: Reference standards: ASTMF150-98--"Test Methods for the Resistance of Conductive and Static Dissipative Resilient Floor Coverings" SJ/T10533-94--"Technical Requirements for Anti-static Technology in Electronic Equipment Manufacturing" JB/T9289-1999----"Technical Requirements for Ground Resistance Meters" SJ/T31469-2002--"Construction and Acceptance Specifications for Anti-static Floors" With the advancement of anti-static coating technology, the use of anti-static floor coatings on concrete or cement floors to prevent static electricity generation is becoming increasingly widespread. Anti-static epoxy floors have characteristics such as a smooth and aesthetically pleasing surface, seamless overall, easy to clean, easy to maintain, long-lasting and effective anti-static effects, and low cost, making them widely applicable in military, aerospace, chemical, electronic manufacturing workshops, warehouses, microcomputer rooms, electrical control rooms, printing factories, textile factories, and all places that require anti-static or explosion-proof flooring. Generally speaking, a film surface resistance value below 1.0×10^10 can eliminate the accumulation of static charges on the surface of the coating. According to the American Society for Testing and Materials (ASTMF150-98) standards, floors with resistance values between 2.5X10^4Ω-1.0X10^6Ω are called conductive floors; while floors with resistance values between 1X10^6Ω-1.0X10^9Ω are called static dissipative floors, both of which can prevent the accumulation of static charges.

In the anti-static floor coating system, it is generally designed as a five-layer structure consisting of a penetrating conductive primer layer, a grounding copper foil network, a conductive leveling layer, a conductive topping layer, and an anti-static surface layer. The coating for the penetrating conductive primer layer should be selected for its strong permeability and should not solely pursue closure to avoid the coating from peeling; the grounding copper foil network should use a flat plastic scraper to compact the self-adhesive copper foil to prevent hollowing; for the conductive leveling layer, care must be taken during construction to ensure the final surface is smooth and flat; for the conductive topping layer, care must be taken to avoid missing spots that could affect the system resistance of the surface layer; therefore, it is advisable to apply two coats during construction.

Currently, most anti-static floor coatings are static dissipative types, which easily guide static charges. However, for anti-static epoxy floors, when the energy of the static electric field reaches a certain level, discharging through the medium can damage some precision electronic components. Therefore, after the anti-static epoxy floor is completed, the first consideration should be the anti-static indicators of the coating. The main indicators include: A. Surface resistance (resistance value between 1.0X10^5Ω-1.0X10^9Ω)—the ratio of the direct current voltage applied between standard electrodes on the material surface to the current between the electrodes after a given energizing time, neglecting possible polarization phenomena on the electrodes. B. System resistance (resistance value between 5.0X10^4Ω-1.0X10^9Ω)—the total resistance between the test surface of the object being measured and the grounding point of the object. C. System grounding resistance (resistance ≤10Ω)—the resistance encountered by the current flowing from the grounding system into the earth and then spreading to another grounding body or far away, which includes the resistance of the grounding wire and the grounding body itself, the contact resistance between the grounding body and the earth, and the resistance of the earth between two grounding bodies or the resistance of the grounding body to the infinitely distant earth.

1. Detection of surface resistance:

(1) Detection tools: Digital megohmmeter: detection voltage of 100V, range of 1.0×10^5～1.0×10^12 ohms, accuracy level not lower than 2.5; standard electrodes: 2 pieces, made of copper, chrome-plated surface, cylindrical, diameter of 63.5mm, weight 2270g; used in conjunction with the megohmmeter to test the surface resistance of the anti-static floor, using conductive rubber as electrode pads (volume resistance <1.0×10^3 ohms). (2) Environmental requirements: Detection should be conducted in an environment with a temperature of 23±8℃ and humidity of 50±5% (maintaining this environment for 24 hours). (3) Detection method: Before acceptance measurement of the anti-static epoxy floor, clean the surface with a clean gauze cloth, and if severely soiled, clean it with a neutral liquid. Then turn on the indoor air conditioning to maintain a certain temperature continuously for 2-3 days, and measure under the specified temperature and humidity conditions. Before placing the electrodes, use a soft cloth to remove all dust from the surface, and the electrode surface should be cleaned with a clean soft cloth soaked in isopropanol of at least 70% concentration and allowed to dry. Connect the positive terminal of the megohmmeter to the ground, place the negative terminal on the floor surface, and read the value after applying voltage for 5 seconds or when the digital reading stabilizes, ensuring the electrodes are positioned about 30mm from the edge, with a distance of no less than 900mm between the two electrodes. For every 46.5m² area, at least 5 tests should be conducted. At least 3 of the 5 tests should include areas that are worn, have chemical spills or water splashes, or are visibly contaminated. 2. Detection of system resistance: (1) Detection tools: Digital megohmmeter: detection voltage of 100V, range of 1.0×10^5～1.0×10^12 ohms, accuracy level not lower than 2.5; standard electrodes: 1 piece, made of copper, chrome-plated surface, cylindrical, diameter of 63.5mm, weight 2270g; used in conjunction with the megohmmeter to test the surface resistance of the anti-static floor, using conductive rubber as electrode pads (volume resistance <1.0×10^3 ohms). (2) Environmental requirements: Detection should be conducted in an environment with a temperature of 23±8℃ and humidity of 50±5% (maintaining this environment for 24 hours). (3) Detection method: Before acceptance measurement of the anti-static epoxy floor, clean the surface with a clean gauze cloth, and if severely soiled, clean it with a neutral liquid. Then turn on the indoor air conditioning to maintain a certain temperature continuously for 2-3 days, and measure under the specified temperature and humidity conditions. Before placing the electrodes, use a soft cloth to remove all dust from the surface, and the electrode surface should be cleaned with a clean soft cloth soaked in isopropanol of at least 70% concentration and allowed to dry. Connect the positive terminal of the megohmmeter to the ground, place the negative terminal on the floor surface, and read the value after applying voltage for 5 seconds or when the digital reading stabilizes, ensuring the electrodes are positioned about 30mm from the edge, with a distance of no less than 900mm between the two electrodes. For every 46.5m² area, at least 5 tests should be conducted. At least 3 of the 5 tests should include areas that are worn, have chemical spills or water splashes, or are visibly contaminated.

In summary, when detecting surface resistance and system resistance, the following factors need to be considered: A. The impact of temperature and humidity: As temperature and humidity increase, the measured resistance value of the epoxy anti-static floor material decreases; surface resistance is more sensitive to humidity, while volume resistance is more sensitive to temperature. With the increase in environmental temperature, the surface of the epoxy anti-static floor is prone to adsorb moisture, leading to increased surface leakage. If the material is hygroscopic, it will also significantly increase the bulk conductivity current. As temperature rises, the adsorption current and conductivity current of the floor material will correspondingly increase. For example, the resistance value of the material at 70°C is only 1/10 of that at 20°C, and with a 10% increase in relative humidity, the resistance value of hygroscopic floor materials will decrease by about one order of magnitude. B. The impact of electrode shape, size, and weight: From both theoretical and practical measurements, a larger and heavier electrode contact area results in a lower measured resistance value, while a smaller and lighter electrode contact area results in a higher measured resistance value. The main purpose of anti-static epoxy flooring is to ensure the elimination of static electricity from the human body, so the size and weight of the electrodes should simulate the size of human shoes and feet, as well as the weight of the human body. C. The impact of test voltage and reading time: The resistance value of the anti-static epoxy floor varies with the magnitude of the test voltage and the duration of the applied voltage. Generally, at room temperature, when the voltage is low, the conductivity current increases linearly with the applied voltage. When the voltage exceeds a certain value, due to increased ionization activity, the growth of current is much faster than the increase in voltage. The higher the test voltage, the lower the measured resistance value.

When the test voltage of normal anti-static epoxy floor material reaches a relatively stable reading time, for systems with high resistance (approximately >1010Ω), the recommended reading time mentioned above may not be sufficient, while for systems with low resistance (<106Ω), a reading time of 5 seconds is more than enough. This is to consider that the reading time should not be too long; otherwise, it will take too much time to take multiple points on-site, leading to low work efficiency. At the same time, if the reading time is too short, there may not be enough time for operations, and the instrument also has a response time.

After completing the measurement, if a second measurement is needed, the electrodes must be short-circuited to release the charged and polarized charges on the electrodes before starting the next measurement. The duration of the short circuit should depend on the material of the floor and the magnitude of the applied voltage. However, it is generally advisable to short-circuit for at least 1 minute. 3. Detection of system grounding resistance: (1) Detection tools: Ground resistance meter: specifications 0~1~10~100 ohms, using a three-pole method to measure ground resistance. The megohmmeter, also known as a shaking table, consists of a high-voltage hand-cranked generator and a magnetic electric dual-moving coil ammeter, providing stable output voltage, accurate readings, low noise, and light shaking, and is equipped with a shielding device to prevent measurement circuit leakage current and independent terminals. (2) Detection method: Disconnect E1 from the grounding system. 1. Along the measured grounding electrode E1, position the potential probe P1 and the current probe C1 in a straight line at a distance of acm from each other, with the potential probe P1 inserted between the grounding electrode E1 and the current probe C1. 2. Use wires to connect E1, P1, and C1 to the corresponding terminals of the instrument. 3. Place the instrument in a horizontal position and check if the ammeter needle points to the center line; if not, use the zero adjustment to align it with the center line. 4. Set the "multiplication scale" to the maximum multiple, slowly turn the crank of the generator while rotating the "measurement scale dial" to make the ammeter needle point to the center line. 5. When the ammeter needle approaches balance, increase the speed of the generator crank to reach over 120 revolutions per minute, and adjust the "measurement scale dial" to make the needle point to the center line. 6. If the reading on the "measurement scale dial" is less than 1, set the "multiplication scale" to a smaller multiple and readjust the "measurement scale dial" to obtain the correct reading. 7. Multiply the reading on the "measurement scale dial" by the multiple on the "multiplication scale" to get the measured ground resistance value. (3) Precautions: A) When using a megohmmeter, first check its condition. Before connecting to the test item, drive the megohmmeter to see if the indicator can rise to '∞', then short-circuit the two terminals, slowly shake the megohmmeter, and the indicator should point to '0'. If it meets the above conditions, the megohmmeter is good; otherwise, it cannot be used. B) If the testing line direction is incorrect or the distance is not long enough, the solution is to find the correct testing direction and distance. C) If the auxiliary grounding electrode resistance is too high, the solution is to pour water at the grounding stake or use a resistance-reducing agent to lower the grounding resistance. D) If the contact resistance between the testing clamp and the grounding measurement point is too high, the solution is to smooth the contact point with a file or sandpaper and ensure the testing clamp is firmly clamped on the smoothed contact. E) For interference issues, adjust the wire laying direction to avoid directions with high interference, reducing fluctuations in instrument readings. F) For instrument usage issues, if the battery is low, the solution is to replace the battery. If the instrument's accuracy decreases, the solution is to recalibrate to zero. G) The measuring lines are 20m and 40m respectively, as when measuring ground resistance, it is required to measure the resistance between the grounding electrode and a distant grounding electrode with a potential of zero. The so-called distant means a certain distance, at which the mutual resistance between the two grounding electrodes is basically zero. Experiments have shown that distances beyond 20m meet this requirement. If the distance is shortened, the measurement error will gradually increase. H) When testing ground resistance, it is required to disconnect the equipment of the protected electrical devices from their grounding terminals. This is because if the protected electrical devices are not disconnected and the ground resistance is too high or the contact is poor, the voltage or current applied to the grounding terminal by the instrument may flow back into the protected electrical devices. If some devices cannot withstand the voltage or current flowing back from the instrument, it may damage the electrical devices. Additionally, some electrical devices may leak current, causing the leakage current to enter the instrument through the testing line, potentially damaging the instrument. Therefore, it is generally required to disconnect the protected electrical devices. J) The surrounding soil composition of the grounding system (ground network) is inconsistent, with different geological conditions, compactness, and moisture levels, leading to dispersion. Surface stray currents, especially overhead ground wires, underground water pipes, cable sheaths, etc., have a significant impact on testing. The solution is to take measurements at different points and calculate the average value.