The crushing stage of conductive carbon black dispersion
Since the usual fineness of conductive carbon black pigments (45 μm) is far from meeting the final requirements of the downstream field, the carbon black must be crushed and dispersed when using Beilum conductive carbon black, and only the carbon black can be crushed and dispersed to a certain fineness. Only within this range can the coloring conductive properties of conductive carbon black or other required properties be fully exerted. As a characteristic of pigments, the degree of fragmentation of carbon black is also related to the “fastness” of its own particles.
Wetting stage during dispersion of conductive carbon black
The interaction between the surface of free carbon black particles and the surrounding medium is an important factor in the wetting of carbon black. The energy relationship of conductive carbon black wetting can be explained by the laws of thermodynamics, in which carbon black surface tension and surface energy are important auxiliary parameters of wetting heat.
The wetting process of Beilum carbon black powder and agglomerates can also be described from a kinetic perspective. The wetting time is not only related to the pores and geometric structure of the carbon black powder, but also increases as the viscosity of the medium increases, and decreases as the wetting tension increases. Under practical conditions, increasing temperature can accelerate the wetting process, but increasing temperature (reducing viscosity) will lead to a reduction in shear force (breaking effect). Therefore, in actual operations, in order to improve the dispersion of carbon black, low molecular weight additives (such as viscosity enhancers or viscosity promoters, etc.) are often incorporated into the medium.
Distribution stage when conductive carbon black is dispersed
By increasing the processing temperature and reducing the viscosity of the system, placing the system under turbulent flow conditions, and extending the residence time of conductive carbon black in the processing equipment, the wetted carbon black particles can be optimally distributed. However, in actual operation, extended residence time will be limited by throughput requirements. Therefore, for the plastics industry, torpedo heads, porous plates, shearing parts, kneading sections and other design measures are usually installed in injection molding machines and extruders to improve the crushing effect and extend the residence time.
Cohesion stage when conductive carbon black is dispersed
Due to the attraction between conductive carbon black particles (dipole, hydrogen bonding and electrostatic force), external energy must be relied on to overcome the attraction in order to achieve the purpose of dispersion. The dispersion of conductive carbon black is closely related to its particle size distribution. Beilum Carbon black with small particle size has a large specific surface area and is thermodynamically unstable, making it prone to re-agglomeration. In actual operations, dispersants are added to coat the surface of carbon black particles, thereby reducing the cohesion between carbon black particles and helping to avoid difficulties in carbon black dispersion operations.