Antistatic Rubber Board Testing

Antistatic rubber sheet testing mainly conducts scientific testing and analysis on the surface resistivity and volume resistivity testing, electrostatic decay time testing, mechanical property testing, chemical medium resistance property testing, wear resistance and anti-slip property testing, dimensional stability and appearance inspections, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Surface resistivity and volume resistivity testing: These are the most core property indicators of the antistatic rubber sheets. The surface resistivities measure the difficulty degrees of the currents flowing along the material surfaces, while the volume resistivities measure the difficulty degrees of the currents passing through the material interiors. Usually required to be within the range of 10^5 to 10^9 ohms, to ensure that the static electricity can be quickly conducted away without becoming the conductive bodies causing the short circuit risks.

Electrostatic decay time testing: This testing assesses the capabilities of the materials to dissipate the static charges. During the testing, a high voltage is applied to the specimens to charge them, then the times required for their surface voltages to decay to 10% or 50% of the initial values are measured. The shorter the decay times, the better the electrostatic dissipation properties of the materials, which is the key parameter of measuring the dynamic antistatic properties.

Mechanical property testing: Including the tensile strengths, elongations at break, tear strengths and hardnesses (Shore A), etc. These testing ensure that the rubber sheets, while meeting the antistatic functions, have the sufficient physical strengths and durabilities, can bear the tensions, extrusions and wears in the actual uses, preventing the functional failures caused by the mechanical damages.

Chemical medium resistance property testing: Assessing the retention rates of the antistatic properties and physical properties of the rubber sheets after contacting the specific chemicals (such as the acids, bases, greases and solvents). The testing method is usually to immerse the samples in the standard chemical reagents for a certain time, then take them out to measure their resistivity, dimension and weight changes, to judge their environmental adaptabilities.

Wear resistance and anti-slip property testing: Especially important for the antistatic rubber sheets used for the floors. The wear resistance is usually tested with the Taber abrasion testing machines, measuring the abrasion amounts at the certain revolutions. The anti-slip properties are assessed through measuring the static friction coefficients, ensuring the use safeties in the key places such as the electronic workshops and operating rooms.

Dimensional stability and appearance inspections: Including the thickness uniformities, lengths, widths, flatnesses, as well as the inspections of whether there are the defects such as the bubbles, impurities, cracks and missing rubber on the surfaces. The dimensional stability testing usually involves placing the samples under the specific temperature and humidity conditions, then measuring their dimension changes, ensuring that the excessive deformations will not occur during the installations and uses.

Testing Scope

Electronic industry and clean room applications: Mainly used for the workbench surfaces, floor mats, shelf liners and tool handles in the production, assembly and testing areas of the electronic components. The testing needs to especially pay attention to the low dust emission, no silicone volatilization and stable electrostatic dissipation capabilities, to prevent the electrostatic discharge (ESD) from damaging the sensitive integrated circuits and electronic assemblies.

Flammable and explosive dangerous places: Applied to the floor laying and equipment linings in the areas such as the petrochemical, powder processing, gas stations and ammunition depots. The testing emphases lie in ensuring that the resistance values are within the explosion-proof safety ranges (usually 10^5-10^8Ω), preventing the static electricity accumulations from igniting the flammable gases or dusts, meeting the national explosion-proof safety regulatory requirements.

Medical and pharmaceutical fields: Used for the floors and equipment work surfaces of the operating rooms, ICUs and sterile pharmaceutical workshops. In addition to the antistatic properties, the testing also needs to cover the special hygiene and safety indicators such as the biocompatibilities (such as the cytotoxicity), antibacterial properties, easy cleaning and disinfection properties, as well as the low volatile organic compound (VOC) emissions.

Logistics and warehousing industries: As the antistatic packaging materials, turnover boxes, pallets and shelf partitions. The testing scope includes the resistance stabilities under the repeated frictions, impacts and different ambient temperatures and humidities, ensuring that the electrostatic sensitive goods can be effectively protected during the transportations and storages.

Special industrial environments: For example, the antistatic conveyor belts and air ducts used in the coal mines. In addition to the routine items, the testing also needs to add the flame retardant properties (such as the alcohol blowlamp burning testing), durability of the antistatic properties and property retention capabilities under the humid and harsh environments.

Office and civil fields: Such as the computer room floors, e-sports room floors and laboratory work surfaces. The testing needs to balance the antistatic properties with the comfort and aesthetics, paying attention to their environmentally friendly and non-toxic characteristics, colour stabilities and property decays during the long-term uses.

Testing Methods

Resistivity testing method (high-resistance meter method): According to the standards such as the GB/T 1410, IEC 60093 or ASTM D257. The high-resistance meters combined with the dedicated electrodes (such as the three-electrode systems) are used for the measurements under the standard temperature and humidity conditions (such as 23±2℃, 50±5%RH). The specified testing voltages (usually 10V, 100V or 500V) are applied, the stable resistance values are read, and the surface resistivities or volume resistivities are calculated.

Electrostatic decay time testing method: Mainly according to the methods such as the ISO 14309, GB/T 3513 or MIL-PRF-87893. The electrostatic decay testers are used, through the corona discharge or contact charging methods, to charge the samples to the specified voltages (such as ±5000V), then automatically recording the times required for the voltages to decay to the specified percentages. The testing is usually carried out under the controllable relative humidities, because the humidity significantly affects the results.

Frictional charging voltage testing method: Simulating the frictional static electricity generation in the actual uses. According to the standards such as the SJ/T 10694, the specific friction materials (such as the nylon cloths and wool felts) are used to rub the rubber sheet surfaces at the specified pressures and speeds, and the non-contact electrostatic voltmeters are used to measure the static potentials generated on their surfaces. This method is used to assess the antistatic properties of the materials under the actual dynamic working conditions.

Mechanical property standard testing methods: The tensile strengths and elongations at break are prepared into the dumbbell specimens according to the GB/T 528 and tested on the tensile testing machines; the tear strengths are tested according to the GB/T 529 (right-angle or trouser specimens); the hardnesses are measured with the Shore type A hardness testers according to the GB/T 531.1. Before all the testing, the specimens need to be conditioned under the standard laboratory environments.

Environmental adaptability testing methods: The chemical resistance testing is carried out according to the GB/T 1690, with the specimens immersed in the selected reagents, testing the property changes after the specified temperatures and times. The wear resistance is tested with the Taber abrasion machines according to the GB/T 9867. For the temperature and humidity resistance, the samples are placed in the constant temperature and humidity chambers or high and low temperature testing chambers, and after the specified cycles, the drifts of the key properties such as their resistances are tested.

Antistatic floor system resistance testing method: For the laid antistatic rubber floors, the system resistance testing needs to be carried out according to the SJ/T 10796 or GB 50174. The two electrodes of the specified weights are used, one placed on the floor surfaces, the other connected to the grounding terminals, measuring the resistances between them, to assess the effectiveness of the entire floor grounding systems.

Testing Standards

Domestic Standards:

1. GB/T 528-2009, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties

2. GB/T 531.1-2008, Rubber, vulcanized or thermoplastic — Determination of indentation hardness — Part 1: Durometer method (Shore hardness)

3. GB/T 1690-2010, Rubber, vulcanized or thermoplastic — Determination of the effect of liquids

4. GB/T 9867, Rubber, vulcanized or thermoplastic — Determination of abrasion resistance using a rotating cylindrical drum device

5. GB/T 3512-2014, Rubber, vulcanized or thermoplastic — Accelerated ageing and heat resistance tests — Air-oven method

6. GB/T 1410, Solid insulating materials — Methods of test for volume resistivity and surface resistivity of solid electrical insulating materials

7. SJ/T 10694, General specification for antistatic testing of electronic products manufacturing and application systems

8. SJ/T 10796, General specification for antistatic access floors

9. GB 50174, Code for design of electronic information system room

International Standards:

1. ISO 37, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties

2. ISO 48, Rubber, vulcanized or thermoplastic — Determination of hardness (10 IRHD to 100 IRHD)

3. IEC 60093, Methods of test for volume resistivity and surface resistivity of solid electrical insulating materials

4. ASTM D257, Standard test methods for DC resistance or conductance of insulating materials

5. ISO 14309, Rubber, vulcanized or thermoplastic — Determination of volume and surface resistivity

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

High-resistance meters and resistance testing electrodes: The core equipment used to precisely measure the high resistance values from 10^3 to 10^14 ohms. The modern high-resistance meters are usually equipped with the programmable voltage sources, digital displays and data recording functions. The parallel plate electrodes or ring electrodes conforming to the standard dimensions and materials must be used, and the shielding boxes are equipped to reduce the influences of the ambient electromagnetic interferences on the measurement accuracies.

Electrostatic decay testers: The instruments integrate the high-voltage charging units, non-contact electrostatic probes (or field strength meters) and high-speed data acquisition systems. Capable of recording the charge decay processes within the millisecond-level times, and automatically calculating the decay times. The advanced models can control the relative humidities of the testing environments, and provide the testing modes conforming to the multiple standards such as the MIL-STD and ESD STM.

Environmental simulation testing chambers: Including the constant temperature and humidity chambers, high and low temperature alternating testing chambers and salt spray testing chambers, etc. Used to provide the standard testing environments (such as 23℃/50%RH) or simulate the extreme use environments (such as the high temperature and high humidity, low temperature and dryness) for the rubber sheet samples, to assess the stabilities and environmental adaptabilities of their antistatic properties.

Mechanical property testing equipment: The electronic tensile testing machines are used to test the tensile and tearing properties; the Shore type A hardness testers are used for the rapid on-site hardness testing; the Taber abrasion testing machines are used to assess the wear resistance; the thickness gauges are used to precisely measure the thicknesses of the various points of the rubber sheets to ensure the uniformities. All these equipment need to be regularly metrologically calibrated.

Electrostatic voltmeters and frictional charging testing devices: The non-contact electrostatic voltmeters (electrostatic field strength meters) are used to measure the surface potentials after the frictions or during the uses. The frictional charging testing devices are the standardized platforms capable of controlling the friction materials, pressures, speeds and strokes, making the frictional charging testing results comparable and reproducible.

Laboratory environmental monitoring systems: Since the temperatures and humidities have the extremely significant influences on the resistivities of the antistatic materials, the professional testing laboratories must be equipped with the precise continuous temperature and humidity monitoring and recording systems, ensuring that the entire testing processes are carried out under the standard specified environmental conditions. This is the prerequisite of ensuring the accurate and reliable testing data.