2. Wire & Cable Applications
Wire & Cable industries consume the largest amount of conductive carbon black, the majority of which is used in the conductor and insulation shields of medium and high voltage cables. Figure 1 illustrates the typical structure of the power cables. The conductor shield may bond with the metal conductor to provide a smooth interface and a homogeneously distributed electric field to the insulation. The insulation shield protects the insulation from corona damage and provides safety. Carbon black in the conductor and insulation shields play a critical role in the long-term service life of the cable.
Depending on the specific application and the type of carbon black, the carbon black loading may vary from ~22% to ~44% by weight. Although not a conductive need, carbon black is also used in the cable jacket to reinforce UV protection.
3. Requirements of Carbon Blacks in Wire & Cable Applications
Carbon black is an essential component used in both the conductor and insulation shields to impart the desired conductivity performance. To choose a carbon black, we can look at desired carbon black loading. The decision is then whether to use a carbon black delivering higher conductivity at lower loading or a carbon black with the lower conductivity at higher loading. However, the carbon black selection depends not only on the required conductivity specification but also on the other requirements including dispersibility, rheology, mechanical performance, and surface smoothness.
As mentioned earlier, the conductivity of carbon black compounds is determined not only by the type and the loading of carbon black, but also by the process conditions including compounding and final cable extrusion. A full understanding of all these aspects ensures optimization of the conductive performance.
3. 1 Dispersibility
Carbon blacks show higher levels of dispersibility with decreasing surface area, lower porosity, and higher structure. As shown in the property-performance relationship in Table 1, with the exception of structure, there is an obvious trade-off between ease of dispersion and delivering high levels of conductivity.
Therefore, when higher conductivity carbon black is required, it is important to find a balance between dispersibility and conductivity. Carbon blacks with differing levels of dispersion are shown in Figure 3.
We can look at a couple of scenarios:
Higher surface area and medium structure carbon black: Here sufficient dispersion energy has to allow full de-agglomeration to the individual aggregates to deliver the optimal conductive performance and other secondary attributes.
Lower surface area and high structure: With this balance of properties the carbon black is highly dispersible and will yield conductive performance but at slightly higher loadings compared to the carbon black described in Scenario 1. This means lower dispersion energy is sufficient to provide good dispersion for the desired conductivity performance. It is worth mentioning that overly aggressive mixing or too much energy input with this type of carbon black can lead to the breakdown of the aggregate (higher structure = more friable aggregate) and hence, deliver lower than the desired performance.
For wire and cable applications, the cleanliness of a carbon black is as important as the conductivity and dispersibility. Higher cleanliness improves dispersion, conductivity, surface smoothness, and reduces screen pack changes in the compounding process.
Birla Carbon’s Ultra technology ensures excellent physical cleanliness; more specifically, low levels of impurities as measured via sieve residue and ash tests.
On the other hand, due to product quality and chemical regulations, chemical cleanliness is also an important requirement. The chemical cleanliness of carbon black can be measured with sulfur, PAH, ionic, and other chemical composition analysis methods.
In addition to the physical and chemical cleanliness, the moisture level present in carbon black also needs to be controlled or minimized prior to compounding as excess moisture adversely affects the dispersion, the conductivity and the surface finish.
The demand of conductive plastics for wire and cable is increasing, and our carbon blacks play a significant role. Birla Carbon is one of the leading carbon black manufacturers and can offer extensive expertise in the wire and cable application arena. We are responding to the various demands of the market with a full portfolio of carbon black products. Our technical experts across the globe stand ready to collaborate with our customers to help them succeed by discovering the right solutions to any application challenges. There are many options when it comes to choosing and using carbon black, so we encourage you to contact a Birla Carbon technical expert to maximize your chances of success.
Additional Blogs for reference
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