Maya Ellison
The effectiveness of antistatic plastics in preventing electrostatic discharge (ESD) is measured through various methods. ESD occurs when there is a transfer of charge between bodies with differing electrical potentials, and it can be dangerous in environments with flammable substances or sensitive electronics. Antistatic plastics are designed to reduce static electricity and protect against ESD. The effectiveness of these plastics is determined by their ability to control the charge during an ESD event and prevent the buildup of static electricity. This is measured through surface resistance, which indicates how easily an electric charge can move across a substance. Static dissipative plastics, for example, have a surface resistance of >1 x 10^5 ohms/square to <1 x 10^12 ohms/square, allowing charges to dissipate within milliseconds. Antistatic plastics have a surface resistivity of 10^10 to 10^12 ohms/square, suppressing triboelectric charging. The effectiveness of these plastics is also influenced by the use of additives, fillers, and the presence of conductive materials.
| Characteristics | Values |
|---|---|
| Dielectric strength | Degree to which a material does not break down and become a conductor under voltage |
| Capacitance | Degree to which a material can store charge |
| Dielectric constant | Measure of how much electrostatic energy a material stores for a given voltage |
| Resistivity | Antistatic plastics have a surface resistivity from 1010 to 1012 Ω/sq |
| Surface resistance | Measures how easily 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 |
| Anti-static plastics | Have a surface resistivity of 1010 to 1012 ohms/cm |
| Anti-static sprays | Reduce static build-up on plastic parts |
| Anti-static additives | Reduce static build-up on plastics |
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What You'll Learn
The role of anti-static additives in plastics
Plastic is an electrical insulator that can support high static build-up. The movement of one material over another can cause charge separation, resulting in static electricity. This can cause handling and contamination issues during transport, storage, and packaging. It can also attract dust, affect performance, damage electronic components, and cause shocks to employees, risking fire.
Anti-static additives are chemicals that can be added to plastics to provide static protection by lowering the resistivity of the material. They are added to polymers to reduce or eliminate the build-up of static electricity on plastic materials. The role of an anti-static additive is to make the surface or the material itself slightly conductive, either by being conductive itself or by absorbing moisture from the air. Anti-static additives can be applied to the surface of products or included during the manufacturing of plastics. They are used for aesthetic reasons and for electrical safety and performance reasons, depending on the end-use application.
Different anti-static additives can be used depending on the level of static protection needed and how long the effect needs to last. For example, short-term additives work by migrating through the polymer matrix towards the surface as it cools. At the surface, they pick up moisture from the atmosphere, resulting in reduced static build-up in the plastic. Other applications need longer-term protection or lower resistivity to prevent sparks and protect electronics from electrostatic dissipation. These applications utilize permanent anti-static agents or conductive additives such as carbon black, conductive fibers, and nanomaterials.
Anti-static additives can also be used in conjunction with static-dissipative plastics to further reduce the risk of electrostatic discharge (ESD). ESD is the transfer of charge between bodies at different electrical potentials and can have catastrophic effects. It can cause anything from a mild to a painful shock and, in extreme cases, loss of life. ESD can also damage sensitive electronic components, causing equipment downtime and costly repairs. Static-dissipative plastics have special properties that help keep electronics from harm, and anti-static additives can further enhance their effectiveness.
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Testing plastic for ESD properties
Surface Resistivity Testing
This method measures how effectively a material resists the flow of electricity across its surface. It indicates whether the material falls within the acceptable range for conductive, dissipative, or anti-static classifications. The surface resistivity of anti-static plastic materials typically ranges from 10^10 to 10^12 ohms/cm, while static dissipative plastics have a surface resistivity greater than 10^5 but not greater than 10^9 ohms/square.
Charge Decay Testing
Charge Decay Testing evaluates the rate at which the material can dissipate a static charge. This test helps determine if the material can safely and effectively eliminate static charges before they reach hazardous levels.
Volume Resistivity Testing
Similar to surface resistivity testing, volume resistivity testing involves placing electrodes opposite the test sample to measure resistance. The volume resistivity is then calculated by multiplying the resistance by the surface area and dividing by the thickness of the part, resulting in a value in ohm-cm.
Compliance with Standards
Certifying ESD plastic products to meet standards such as ANSI/ESD S20.20 or IEC 61340 can provide assurance to customers and protect manufacturers from liability. IEC 61340 is an international standard that outlines methods for measuring electrostatic properties and ensures compliance in various industries.
It is important to select a reputable supplier for ESD plastics who can provide technical support and expertise in addition to high-quality materials. Additionally, it is worth noting that the first step in preventing ESD buildup is to reduce friction and eliminate unnecessary activities and materials that create static charges.
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How anti-static plastics prevent electrostatic discharge
Plastics are insulators, meaning they prevent the flow of electrons across their surfaces or through their volumes. This is distinct from conductors, such as metals, which readily support electron flow. However, the accumulation of static electricity in plastics can lead to sudden electrostatic discharge (ESD), which can be highly destructive.
ESD is the transfer of charge between bodies at different electrical potentials. It can occur when there is a rubbing, sliding, or breaking of material, generating electrostatic voltages. This can result in sparks, which are especially dangerous in environments with flammable liquids, solids, or gases. ESD can also be harmful to humans, ranging from mild to painful shocks and, in extreme cases, loss of life.
To prevent ESD, anti-static plastics are used. These plastics have a surface resistivity of 10^10 to 10^12 ohms/cm, which helps to suppress triboelectric charging (the creation of electric charge by rubbing one material against another). Anti-static plastics can suppress initial charges, prevent the build-up of static electricity, and slowly decay static charges. They achieve this by turning static electricity into current electricity, creating a circuit that carries the electric charge away harmlessly.
Anti-static plastics are created by adding fillers or additives to the plastic to improve its conductivity. These fillers can be non-carbon alloys, carbon powders, carbon fibres, or stainless-steel fibres. However, adding fillers can reduce the material's strength and effectiveness and affect its physical properties. Therefore, it is essential to choose the appropriate filler or additive for the specific application.
The effectiveness of anti-static plastics is measured through surface resistivity, which determines how much static charge can accumulate on the material. A good anti-static plastic should have a surface resistivity of 10^6 to 10^8 ohm/square. Additionally, the humidity of the environment impacts the performance of anti-static plastics, with higher humidity resulting in better antistatic performance.
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Differences between anti-static and static-dissipative plastics
The effectiveness of antistatic plastics is measured through their surface resistivity, which is typically between 10^10 and 10^12 Ω/sq. This property helps suppress initial charges, prevent the build-up of static electricity, and slowly decay static charges.
Now, let's delve into the differences between anti-static and static-dissipative plastics:
While both anti-static and static-dissipative plastics are designed to reduce the risk of electrostatic discharge (ESD), there are distinct differences in their properties and applications:
- Function: Anti-static plastics focus on suppressing initial charges and preventing the accumulation of static electricity. On the other hand, static-dissipative plastics are designed to dissipate or guide electrical charges to the ground in a controlled manner. This prevents discharges to or from human contact, making it safer for people handling electronic devices.
- Surface Resistivity: Anti-static plastics have a higher surface resistivity, typically ranging from 10^10 to 10^12 ohms/cm (or Ω/sq). This higher resistivity inhibits triboelectric charging, which is the creation of electric charges through the rubbing or contact of different materials. Static-dissipative plastics, however, have a lower surface resistivity, typically greater than 1 x 10^5 ohms/square but less than 1 x 10^12 ohms/square. This range allows static-dissipative materials to guide charges to the ground safely.
- Charge Dissipation Speed: Static-dissipative plastics allow charges to dissipate rapidly, typically within milliseconds. In contrast, anti-static plastics provide a slower rate of decay for static charges, ranging from a hundredth of a second to several seconds.
- Applications: Both types of plastics are used in various industries, including automotive, packaging, medical devices, electronics, and appliances. However, the choice between anti-static and static-dissipative plastics depends on the specific application requirements. For instance, in an environment with flammable liquids or gases, static-dissipative plastics might be preferred to prevent sparks that could cause fires or explosions.
- Material Composition: The difference in properties between anti-static and static-dissipative plastics is often due to variations in their material compositions. For instance, ULTREX® Anti-static incorporates an additive that attracts moisture from the air to the plastic's surface, aiding in reducing static charge build-up. In contrast, ULTREX® Static Dissipative incorporates a carbon-based conductive additive to enhance the dissipation of static charges.
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The use of conductive fillers in anti-static plastics
The use of conductive fillers in plastics is a common method to prevent electrostatic discharge (ESD). ESD is the transfer of charge between bodies at different electrical potentials, which can have catastrophic consequences, including damage to sensitive electronic components, loss of life in extreme cases, and fires or explosions in flammable environments.
Conductive fillers are added to polymers to improve their thermal and electrical conductivity. These fillers create "pathways" or "continuity" for energy to pass through the polymer. The most common fillers include metal powders, carbon black, CNTs, graphite, inherently conductive polymers, boron nitride, and talc.
Carbon fillers, such as carbon powders and carbon fibres, are particularly effective in preventing ESD. Carbon powders form a conductive path when particles touch, while carbon fibres stretch to make a conductive path and dissipate electric charge more efficiently. Stainless-steel fibres also dissipate electric charge effectively, as the strands stretch and touch, creating a conductive path.
The addition of conductive fillers can be tailored to the specific needs of the application. For example, the amount of nanographite filler added to a polymer can be adjusted to achieve the desired electrical resistivity. Similarly, conductive fillers can be multifunctional, such as magnetically functionalized self-aligning graphene, which provides high heat dissipation and electrical shielding for energy storage devices.
Conductive fillers are also used in anti-static coatings, which can be applied externally to the surface of materials or internally by blending them into the plastic during processing. These coatings can provide static dissipation, ESD protection, EMI/RFI shielding, or thermal management.
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Frequently asked questions
ESD is the transfer of charge between bodies at different electrical potentials. This sudden flow of electricity can have catastrophic effects, from causing a mild shock to a person to destroying sensitive electronic components. Plastics are electrical insulators, meaning they can accumulate surface electrostatic charges that stay on the surface until discharged. Measuring the anti-static effectiveness of plastics helps to ensure human safety and protect electronic devices.
Anti-static effectiveness for plastics is measured by evaluating their surface resistivity or resistance. Surface resistivity is measured in ohms/sq or ohms/cm, with anti-static plastics typically having a range of 10^10 to 10^12. Anti-static materials inhibit triboelectric charging, which is the buildup of electric charge through rubbing or contact with another material.
One method is to rub another material against the plastic to observe if either becomes charged. Another technique is to sandwich the plastic between two metal bars and measure resistance or insert probes to pass a current through them while measuring with additional probes. ASTM D257 is a standard for measuring volume resistivity, which involves calculating resistance times the surface area (cm^2) divided by the thickness of the part (cm), yielding ohm-cm.
There are several approaches to reducing static buildup on plastics. Anti-static additives, such as carbon powders or fibres, can be blended into the plastic material. External additives can also be sprayed or coated on, but there is a risk of them rubbing off. Anti-static sprays and cleaners can be used when adding additives is not an option. Slip agents, which are inexpensive lubricants, can be added to reduce friction and the likelihood of static buildup.
