1.Conductive carbon black
Ordinary carbon black itself has certain conductivity. DBP value is generally 30~80. Conductive carbon black is a collective term, it refers to the special carbon black of which the conductivity is stronger than ordinary carbon black and color carbon black. In terms of production methods, conductive carbon black can be divided into acetylene carbon black, heavy oil furnace carbon black, heavy oil gas by-product carbon black.
According to different conductivity, from low to high, divide into Conductive Blacks, SCF Super Conductive Blacks, and XCF Extra Conductive Blacks. To measure with DBP, DBP value of ordinary carbon black is below 100, that of CF conductive carbon black is 100 ~ 160, that of SCF superconducting carbon black is 160 ~ 260, and that of XCF special conductive carbon black can reach 300 ~ 350.
2. Application of conductive carbon black
Conductive carbon black application has two aspects: add into rubber and plastics etc. as conductive filler; be used in batteries. As a conductive filler, conductive carbon black is added into rubber, plastics and other polymers to form carbon black - polymer composite materials. The conductivity of the carbon black-polymer composites depends on the conductivity of the carbon black. With different conductive properties, it can have conductive, anti-static, electromagnetic shielding and other effects. Conductive plastics and rubber fillers are mainly conductive carbon black, graphite, carbon fiber, metal powder, metal fiber and glass fiber. Among them, carbon black filler is the mainstream, and carbon black filled conductive polymer is the most widely used. This is because the conductive carbon black has small density, low costs, and is easy to disperse and process in the polymer materials. Besides, according to different electrical conductivity needs, carbon black offers more choices with lasting and stable conductivity. Resistance of its finished products can vary in the range of 100 -109Ω•cm; conductivity is lasting and stable. But its products are limited to black, and have a great impact on the performance of materials, and supporting modified technology is needed.
3. How to select index of superconducting carbon black
The fundamental principle of carbon black conductivity is that the distance between carbon particles and the number of the particles in carbon black agglomerates (clusters formed by multiple aggregates) decide conductivity of carbon black compound. It’s like metal conductivity is better if the wire is thicker. So people can choose conductive carbon black in the following ways.
(1) Oil absorption, that is, the structure of carbon black. High-structural carbon black has high conductivity.
(2) Reduce the content of ash, impurities, sieve residue and other non-carbon materials, and relatively increase carbon black content in the rubber.
(3) Particle size is small and generally 20-40nm. The general size of conductive carbon black is concentrated in this scope.
(4) Volatile matter is low, surface oxygen-containing groups are few, presenting neutral carbon black.
(5) Solvent extract is low, and the insulating layer won’t be formed easily.
(6) High iodine absorption, and empty-shell carbon black is the best.
(7) Good dispersion, carbon black uniform dispersion is directly related to effective ingredient increase of carbon black.
(8) It’s better to process carbon black after heating.
4. Influencing factors of conductivity
4.1 Impact on carbon black performance
Fill carbon black into high polymer material. This will reduce its volume resistivity, and the reduction degree is decided by the performance of carbon black particles and its filling. When the other characteristics of carbon black are the same, if its primary particles are fine, the primary aggregates will be small, and volume resistivity of the high polymer mixture will be low. Increase carbon black structure, and volume resistivity of the high polymer mixture will be reduced. The basic performances of high-conductivity carbon black must be a small particle size, specific surface area, highly developed structure, little floating π electron impurities, high degree of graphitization and porosity. The content of carbon black in high polymer materials directly influences formation of conductive networks. To give the high polymer material conductivity, its carbon black content must reach the critical concentration. Different conductive carbon black has different critical concentrations in the same polymer.
4.2 The impact of high polymer materials
For different types of rubber, their carbon black composite materials have different conducting effects. The order of access to gain conductivity: EPDM rubber, neoprene, natural rubber, nitrile rubber, styrene butadiene rubber. Silicone rubber is suitable for making conductive rubber materials in large batches.
4.3 The impact of processing conditions
Carbon black is filled into the polymer material. Due to influence of the processing conditions, carbon black dispersion and structural damage are different, resulting great conductivity difference. Therefore, in the dispersion process of polymer materials, carbon black needs to avoid inadequate dispersion or over-dispersion in order to achieve the best dispersion state. The order of impact on conductivity from high to low: injection molding, extrusion molding, calendering molding, compression molding. Pressure vulcanization and extended curing time will make the resistivity lower.
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