The crushing stage during the dispersion of conductive carbon black
Since the usual fineness (45μm) of conductive carbon black pigments is far from meeting the final requirements of the downstream field, it is necessary to crush and disperse the carbon black when using conductive carbon black, and the only way to crush and disperse the carbon black to a certain fineness In this range, the conductive carbon black's coloring conductivity or other required properties can be brought into full play. 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 of the free carbon black particle surface with the surrounding medium is an important factor for carbon black to be wetted. The energy relationship of conductive carbon black wetting can be explained by the laws of thermodynamics, in which the surface tension and surface energy of carbon black are important auxiliary parameters of the heat of wetting, and the wetting process of carbon black powder and agglomerates can also be described from a kinetic point of view. The wetting time is not only related to the porosity and geometric structure of the carbon black powder, but also increases with the viscosity of the medium and decreases with the increase of the wetting tension. Under practical conditions, increasing the temperature accelerates the wetting process, but increasing the temperature (decreasing the viscosity) leads to a decrease in the shearing force (crushing action). Therefore, in order to improve the dispersibility of carbon black in actual operation, low molecular weight additives (such as plasticizer or viscosity accelerator, etc.) are often mixed into the medium.
Distribution stage of conductive carbon black dispersion
By increasing the processing temperature and reducing the viscosity of the system, the system is under turbulent conditions; and the residence time of the conductive carbon black in the processing equipment is prolonged; the wetted carbon black particles can be better distributed. However, in practice, extended dwell times will be limited by throughput requirements. Therefore, for the plastics industry, torpedo heads, perforated plates, shearing parts, kneading sections and other design measures are usually installed in the injection molding machine and extruder to improve the crushing effect and prolong the residence time.
Cohesion stage during dispersion of conductive carbon black
Due to the attraction (dipole, hydrogen bond and electrostatic force) between the conductive carbon black particles, it is necessary to rely on external energy to overcome the attraction to achieve the purpose of dispersion. The dispersion of conductive carbon black is closely related to its particle size distribution. Carbon black with a small particle size has a larger specific surface area and is thermodynamically unstable, which is prone to re-agglomeration. In actual operation, adding a dispersant to coat the surface of carbon black particles reduces the cohesion between carbon black particles and helps to avoid difficulties in carbon black dispersion operations.
The above are the four stages that conductive carbon black needs to go through in the process of dispersion. If you want to get better dispersed conductive carbon black, you can start with these four stages.