Conductive Plastics FAQ

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1. How can you successfully use the Beki-shield® product?
2. What is EMI shielding and how can the Beki-shield® product increase shielding effectiveness?
3. What is ESD protection and how can the Beki-shield® product improve it?
4. Why should I use the Beki-shield® product to make my plastics conductive?
5. How does the Beki-shield® product affect the mechanical properties of the end product?
6. Which requirements are important to select the right Beki-shield® product?
7. What load % is needed to reach the right levels of shielding effectiveness or ESD protection?
8. Is my processing equipment damaged by the stainless steel fibers in the Beki-shield® product?
9. How can I get support for the selection of the right Beki-shield® product and a quote?
10. Does the Beki-shield® product increase the strength of the final product?

Answers

1. How can you successfully use the Beki-shield® product? 
The most important aspect for successful use of the Beki-shield® product is to make sure that the amount of shear is sufficient to open the pellets but not too much to break up the fibers in the  conductive network. The Beki-shield® grains, which contain stainless steel fibers, provide electrical conductivity by making a conductive network in the plastic part. If the shear forces are excessive, the fiber length is reduced too much, and it will become more difficult for the fibers to form the network. If this happens, the electrical conductivity of the final part will be reduced. On the other hand, it is important to have a certain amount of shear present during the processing, as shown in the figure below. Insufficient shear leads to granulates, which will also make it difficult for the stainless steel fibers to form a conductive network.

Relation of SE (= Shielding Effectiveness) vs SHEAR FORCES

Our datasheets provide clear recommendations on the parameters that influence the shear during the compounding and injection molding processes. Bekaert’s experienced application engineers are also available to help you fine-tune the settings of your processing to make sure you reach the best conductivity possible with our Beki-shield® products.

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2. What is EMI shielding and how can the Beki-shield® product increase shielding effectiveness?

Electromagnetic Interference (EMI) is caused by electromagnetic waves, which can originate from all sorts of different man-made or natural sources (e.g. lightning, power converters, radio antennas, wireless connection, computer clocks, ….). These electromagnetic waves can disturb the proper functioning of sensitive electronic equipment. In some cases, this interference is unacceptable and the correct functioning of your equipment needs to be guaranteed (e.g. anti-collision sensors in a car, EMG equipment, ….). In these cases it is required that a barrier is created in the housing (conductive plastic) which can act as a shield to prevent electromagnetic waves from leaving their source or entering the equipment which needs to be protected.

The barrier functions on the principle of the Faraday cage. As shown in the figure below, the Faraday cage will ensure that the power of the incoming wave is reflected and absorbed. By doing so it will reduce the power of the outgoing wave. The shielding effectiveness (SE) of this boundary is a clear indication of how well the boundary can reduce the incoming power of the electromagnetic wave. The higher the SE, the better the boundary will prevent electromagnetic waves from leaving their source or from entering the electrical device.

Shielding effectiveness is determined by the frequency, the distance from the source, the type of electromagnetic field (near or far field), the magnetic permeability, the electrical conductivity and the thickness of the boundary. The stainless steel fibers of the Beki-shield® product will make sure that the plastic housing of your electronic equipment reaches extremely high levels of electrical conductivity and thus high levels of shielding effectiveness at very low load levels. This is shown in the figure below, which compares nickel-coated carbon fiber, carbon fiber and Beki-shield®. Our white paper goes into more detail on the exact functioning of EMI shielding and how Beki-shield® provides the highest shielding effectiveness possible.

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3. What is ESD protection and how can the Beki-shield® product improve it?

Electrostatic discharge (ESD) is a common phenomenon in daily life, usually experienced as a small electric shock after touching a metal item that is electrically isolated from the ground. ESD is caused by the difference in electrical charge between an electrically loaded item and the ground. In most cases this phenomenon is rather harmless, but in some situations it can cause damage to electronic equipment, or lead to dangerous situations in explosion-proof environments.

To prevent electrostatic charges from building up and releasing as sparks, the metal fibers from the Beki-shield® product, when added to a plastic component, create a conductive matrix. In this way the electrical charges can be reduced by “bleeding off” over the grounded part, or from contact with the air. The Beki-shield® product performs an additional valuable role by allowing metal parts to be replaced with lightweight plastic parts. Furthermore, it gives you the option to color your final product while maintaining the required electrical conductivity. Our white paper provides more information on ESD protection and how the Beki-shield® product can improve it.

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4. Why should I use the Beki-shield® product to make my plastics conductive?

The Beki-shield® products consist of stainless steel fibers that provide very high levels of conductivity at very low load levels. This is particularly interesting when you need to reach high levels of electromagnetic interference (EMI) shielding or electrostatic discharge (ESD) protection at low load levels. The low load levels give you the possibility to color your end product and (in comparison with carbon black) you will have non-sloughing end products, such as castor wheels which do not leave marks on floors. Low load levels also mean that mechanical properties such as impact strength and part shrinkage are not significantly affected. The Beki-shield® product is easy and safe to use in your injection molding or compounding process and enables you to design lightweight, complex components with long-lasting conductivity. It is ideal to replace metal components that require EMI shielding properties with lightweight plastic alternatives that have high EMI shielding effectiveness.

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5. How does the Beki-shield® product affect the mechanical properties of the end product?

Due to the very low load levels, which are needed to reach the right levels of electrical conductivity for electromagnetic interference (EMI) shielding or electrostatic discharge (ESD) protection, the Beki-shield® products have an insignificant impact on the mechanical properties of the end product. This is clear from the figure below which compares carbon fiber (CF) with the stainless steel fibers of the Beki-shield® product. You can see that the reduction in impact strength to reach the same level of EMI shielding is significantly less with the stainless steel fibers of the Beki-shield® product than with the CF product. Do not hesitate to contact us for more information on the test below or other mechanical properties.

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6. Which requirements are important to select the right Beki-shield® product?

The most important requirement is to make sure that your base polymer is compatible with the polymer coating and/or the sizing of the Beki-shield® grains. Our datasheets provide clear recommendation of which base polymers are compatible with our different types of Beki-shield® grains. The second most important consideration is the processing temperature. This should be in the range defined in the datasheets to make sure that the sizing and/or the coating dissolves correctly. (Depending on the type of product, only sizing will be present, or sizing and coating). This will ensure that all the grains open up easily and disperse well in order to create a good electrically conductive network in the plastic component.

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7. What load % is needed to reach the right levels of shielding effectiveness or ESD protection?

With the stainless steel fibers from the Beki-shield® product you can already reach very high levels of conductivity at extremely low load levels. The table below indicates the EMI shielding effectiveness and ESD protection values possible with the Beki-shield product. The most important aspect to make sure you reach these values is to limit the shear forces on the stainless steel fibers of the Beki-shield® products. Excessive shear forces will reduce the length of the fibers too much, impairing their ability to form the network, and consequently reducing the electrical conductivity of the final part.

(*) resin density: ± 1 g/cm³ - stainless steel fiber density: ± 8 g/cm³
(**) 30-1000 MHz shielding range

Our datasheets provide clear recommendations of the parameters that influence the shear during the compounding and injection molding processes. Bekaert’s application engineers are also available to help you fine-tune the settings of your processing so that you reach the best conductivity possible with our Beki-shield® products.

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8. Is my processing equipment damaged by the stainless steel fibers in the Beki-shield® product?

Along with the Fraunhofer Institute in Germany, Bekaert has conducted extensive research on the impact of stainless steel fibers on the wear of processing equipment. Tests were performed with four different polymer compounds containing four different types of fillers. In the DKI platelet test we analyzed the wear on test plates that consisted of steel typically used to manufacture cylinders or barrels of extruders. The measurements of the weight loss of the test plates and visualization of the wear pattern by chromatic confocal microscopy gave a clear indication of the impact on the wear by the different filler materials. The table below shows that the stainless steel fibers of the Beki-shield® product make no difference to wear compared to the results obtained with the pure polymer without filler materials. This is mainly due to the fact that the stainless steel fibers are very ductile, and only low amounts need to be added to reach the desired levels of conductivity. Do not hesitate to contact us for more information or to receive the complete test report.

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9. How can I get support for the selection of the right Beki-shield® product and a quote?

Please contact our headquarters. We will put you in touch with the relevant R&D and technical application engineers who can help you select the right material or can design the right product specifically for your needs. Also in the other regions outside Europe we have highly skilled technical and commercial people available who can respond to your specific requests.

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10. Does the Beki-shield® product increase the strength of the final product?

The Beki-shield® product does slightly increase the strength of the final product. If you are looking for solutions specifically to increase the strength of plastics and composites through the use of stainless steel fibers, check out our detailed information on composite reinforcement with stainless steel fibers.

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