Antistatic vs. Static Dissipative Plastics
To understand the meaning of Antistatic vs. static dissipative, we first need to understand the meaning of static electricity. As the name implies, it is electricity at rest. The electrical charge transfers electrons that occur when there is a rubbing, sliding, or breaking of material, generating electrostatic voltages.
Talking about electrostatic discharge (ESD) plastics, These plastics are designed to reduce the static electricity to protect electrostatic-sensitive devices or limit flammable gases or liquids. These plastics are available in many types, anti-static and static dissipative being the two most prominent ones.
The Importance of Antistatic and Static Dissipative Plastics –
Build-up static electricity can occur in an insulating material like plastic when the charge tends to stay in the restricted areas of the contact between the materials. This electrostatic voltage can later be discharged with an arc or spark when it comes in contact with a body with a significantly different electrical potential. Good examples are the human body and microcircuit.
Electrostatic discharge, a sudden flow between two electrically charged objects, can have disastrous effects. Coming in contact with ESD, a person can face a mild to strong shock and, in worst cases, DEATH. Electrical sparks even bigger bad news for environments containing flammable gases and liquids. But the most common fatalities of ESD are sensitive electronic components. Some micro-electronic parts can be damaged or destroyed by ESD as low as 20 volts.
The ESD damage to a component can result in wrong readings, periodic breakdowns, and even permanent, unrepairable damage. All that can trigger production downtime and expensive repairs. The main reason to use Antistatic and static dissipative plastics is to slash the risk of ESD and reduce malfunctions significantly.
Antistatic vs. Static Dissipative –
For conductive thermoplastics, the categorization is completely dependent on their surface resistance. That’s a metric of measuring how seamlessly an electric charge can travel across a substance.
Static dissipative plastics have a surface resistance of >1 x 105 ohms/square <1 x 1012 ohms/square and lets electrical charges dissipate typically within milliseconds. Static dissipative materials allow the charges to flow to the ground slowly and in a more guided or controlled manner preventing discharge to human contact.
On the other hand, Anti-static plastic materials have a surface resistivity of 1010 to 1012 ohms/cm and suppress triboelectric charging (The creation of electric charge by rubbing one material to another). Antistatic plastics are capable of suppressing initial charges and preventing the build-up of static electricity and very slowly decays static charge from a hundredth of to several seconds.
Conventional anti-static and static dissipative parts have proved themselves tremendous help reduce ESD without trading off on the strength, chemical, physical, mechanical, and thermal properties. The most common application for anti-static and static dissipative is found in automotive, packaging, medical devices, appliances, and electronics & electrical.
Interesting Read – What is Shore Hardness Scale? | The Complete Guide
Resistivity Test Methods –
Source - gotopac.com
As said earlier, for thermoplastic materials intended to dissipate electrostatic charges, surface resistivity si the most preferred measurement method to do so.
Within the surface resistivity method, there are several measurement techniques that can be utilized. However, the most accepted test method is ASTM D257. It comprises measuring resistance via an ohmmeter between two electrodes applied under load to the surface being tested. The thermoplastic’s heterogeneous makeup leads to the usage of electrodes instead of point probes.
Simply touching the surface with a point do contact might not give accurate readings consistent with the overall part. It is crucial to maintain good contact between the sample and electrodes, which requires a significant amount of pressure. The resistance reading is then converted to resistivity to account for the dimensions, which can alter depending on the shape and size of the test samples.
As shown in the image above, Surface resistivity is equal to resistance times the perimeter of the electrodes divided by the gap distance, yielding ohms/square.
Source - gotopac.com
Volume resistivity is utilized for assessing the relative dispersion of a conductive additive throughout the polymer matrix. It can be roughly compared and related to EMI/RFI shielding effectiveness in some conductive fillers.
The technique of testing in volume resistivity is quite similar to surface resistivity. However, electrodes are placed opposite to the test sample. ASTM D257 also relates to volume resistivity ad a conversion factor again completely dependent on electrode dimensions, and part thickness used to get the resistivity value from a resistance reading.
Volume resistivity calculation as per the image above – resistance times the surface area (cm2) divided by the thickness of the part (cm), yielding ohm-cm.
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1. What is the difference between static dissipative and conductive?
Ans. Static dissipative materials are classified based on their electrical resistance properties. Their resistance is measured in ohms (as already explained well above). On the other hand, conductive parts are measured by their low curing temperature.
2. What is the static dissipative range?
Ans. Static Dissipative materials are typically in the surface resistance range of 1×10 5 ohms/square but less than 1×10 11 ohms/square.
3. What are ESD safe materials?
Ans. ESD safe materials are often created by blending an optimized based material – ABS, PETG, or PC with an additive are the prime examples. The base material plays an important role in determining the mechanical properties of the finished part, such as strength and flexibility.
4. Is PEEK material ESD safe?
Ans. Yes, PEEK material is ESD safe, and thus it is extensively in the electronics and electrical industries. PEEK ESD has fabulous dimensional stability and can be processed quite easily in tight tolerances.
5. Is PVC static dissipative?
Ans. PVC 300 is a widely available plastic sheet that is static dissipative. It is designed to control static electricity for a wide range of end uses.
That was my take on Antistatic vs. Static Dissipative Plastics. I want to say that ESD-proof plastics are quite common, and they’ve successfully made their way into the mainstream plastic industry. Utilizing them properly after determining all the necessary readings can make your products 100% safe for human contact.