news

The two core indicators of carbon black are primary particle size and structural properties (characterized by oil absorption), which together determine blackness, dispersibility, and conductivity.

1. Primary particle size

Primary particle size refers to the primary particle diameter of carbon black.

The smaller the particle size, the larger the specific surface area. The stronger the light absorption ability, the higher the blackness; But as the specific surface area increases, the adsorption force on the particle surface becomes stronger, the tendency for powder agglomeration becomes severe, and the difficulty of dispersion increases, requiring more dispersants and higher shear energy. At the same time, the particle spacing is easier to narrow, the probability of particle contact is increased, and the conductivity is better.

The larger the particle size, the smaller the specific surface area and the lower the blackness; Weak agglomeration force makes dispersion easier; The gaps between particles are large, making it difficult to establish conductive pathways and resulting in poor conductivity.

Shortcoming: Ultra small particle size carbon black, when poorly dispersed, may cause agglomerated particles, resulting in black spots, graying, and poor blackness.

2. Carbon black structure

Structural description refers to the degree to which particles adhere to each other and form chain like or branched aggregates, measured by DBP oil absorption value.

High structure carbon black: well-developed chain branches and rich spatial network structure.

✅  Conductivity: It is easier to overlap and form a continuous conductive path, with excellent conductivity performance;  

✅  Dispersion: The resin/solvent inside the chain like structure has a high oil absorption value, a significant increase in system viscosity, and greater dispersion resistance;  

❌  Blackness: Chain structure scatters light, and at the same particle size, blackness is lower than that of low structure carbon black.

Low structure carbon black: compact aggregates, few chain branches, low DBP oil absorption value.  

✅  Blackness: Dense aggregates, less light scattering, higher blackness, strong coloring power;  

✅  Dispersion: Low oil absorption, minimal impact on system viscosity, relatively easy dispersion;  

❌  Conductivity: Particles lack chain like overlap, making it difficult to form a continuous conductive network and resulting in poor conductivity.

4. Formula selection logic

1. High blackness coloring system (ordinary black paint, ink): Priority is given to small particle size+low structure carbon black. Balancing high blackness, controlling viscosity, and reducing dispersion pressure.

2. Conductive/anti-static coatings: prioritize small particle size and high structure carbon black. Building conductive pathways through chain like structures; The disadvantages are high oil absorption, high system viscosity, and limited addition amount.

3. Easy to disperse and economical coloring: Large particle size and low structure carbon black is selected, which is easy to disperse but lacks sufficient blackness.

The oxygen-containing groups on the surface of carbon black can also have auxiliary effects: carbon black with high surface oxygen-containing groups has better wetting properties and easier dispersion, but it can damage the conductive path and reduce conductivity.

The primary particle size and structure of carbon black are key parameters that affect its blackness, dispersibility, and electrical conductivity. The smaller the original particle size, the higher the specific surface area, and the blackness and conductivity of carbon black are improved. However, the tendency of particle aggregation is enhanced, and the difficulty of dispersion increases. The structure of carbon black is usually characterized by its DBP oil absorption value. High structured carbon black has well-developed chain branch aggregates, making it easy to construct a continuous conductive network and exhibiting excellent conductivity; But its high oil absorption significantly increases the viscosity of the system, increases the difficulty of dispersion, and has stronger light scattering effect. At the same particle size, the blackness is not as good as that of low structure carbon black. Low structured carbon black aggregates are dense, have weak light scattering, higher coloring blackness, have little effect on system viscosity, are easier to disperse, but difficult to form continuous conductive pathways, and have poor conductivity. In the design of coating and ink formulations, small particle size and low structure carbon black are often used as coloring systems; The conductive anti-static system prioritizes the use of small particle size and high structure carbon black, and can adjust the wettability and conductivity properties by combining with the functional groups on the surface of the carbon black.