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Home / News / Industry News / Carbon Black Has Been Ground for a Long Time — Why Is Fineness Still Not Improving?
Industry News
Epoxy Colour Paste · Industrial Coatings · Carbon Black Dispersion · DH-6200
In epoxy floor coatings, industrial coatings, and related inks, black colour paste is widely used. What looks like simply grinding carbon black into resin frequently presents challenging production problems: viscosity rising noticeably when carbon black is added; grinding time already extended but fineness not improving; state looking normal right after production but re-coarsening or viscosity change appearing after storage. These phenomena do not necessarily mean the grinding equipment has a problem. Carbon black's own particle structure, surface properties, and addition level all affect the dispersion process.
Carbon Black Addition Makes Paste Viscosity Rise Sharply
Carbon black particles are very fine and easily form inter-particle network structures at higher addition concentrations. If wetting is not ideal, paste flowability drops rapidly. Simply adding more resin to dilute reduces pigment concentration and affects colour paste use cost.
Grinding Time Increased — Fineness Still Not Improving
Grinding equipment provides mechanical action to progressively open larger agglomerates. But if wetting between carbon black and grinding base resin is poor, extending grinding time may not bring the expected change — and may increase equipment wear and energy consumption.
Different Carbon Black Grades Need Different Dispersion Approaches
Low-surface carbon black and high-surface carbon black differ in particle state and specific surface area. Especially high-surface carbon black — at the same addition ratio, its demand for dispersant may increase significantly. After switching carbon black grade, the original dispersant addition ratio should not be directly copied.
Colour Paste Re-Coarsens or Viscosity Changes After Storage
If the dispersion state does not maintain stability, pigment may re-agglomerate during storage — manifesting as re-coarsening, sedimentation, or viscosity change. Paste evaluation cannot only check fineness right after production.
DH-6200: Dispersant for Epoxy and Related Resin Systems
DH-6200 is a dispersant suited for epoxy systems — applicable for carbon black and organic pigment grinding dispersion, and also suitable for solvent-free epoxy black colour paste, unsaturated resin colour paste, and polyether/polyester polyol colour paste formulations.
In use, DH-6200 can first be added to the grinding base resin mixture, then carbon black or organic pigment added for grinding — allowing the dispersant to participate in pigment wetting at the start of grinding. Reference addition ranges by pigment type: inorganic pigments 7%–15%; low-surface carbon black 10%–20%; high-surface carbon black 40%–80%. Beyond epoxy coatings, DH-6200 can also be applied to carbon black and organic pigment dispersion in alkyd and polyurethane related ink systems.
In actual testing, setting different addition ratios for comparison and simultaneously observing grinding fineness, paste viscosity, colour development state, and post-storage changes, then confirming the appropriate ratio for the current formulation, is recommended.
Summary
Epoxy black colour paste developing high viscosity, slow fineness reduction, or re-coarsening after storage is not simply a grinding problem. Carbon black grade, addition concentration, resin properties, and dispersant matching all affect the final colour paste state. Especially in high-concentration carbon black formulations, different carbon blacks may have significantly different dispersant requirements. After switching pigment grade, the dispersant addition ratio needs re-evaluation. Testing should include storage state alongside initial fineness as part of the complete evaluation.
Inorganic Pigments
7%–15% of pigment weight
Low-Surface Carbon Black
10%–20% of pigment weight
High-Surface Carbon Black
40%–80% of pigment weight
Frequently Asked Questions
Why is the recommended dosage for high-surface carbon black (40–80%) so much higher than for inorganic pigments (7–15%)?
The dosage is expressed as a percentage of pigment weight, and the dramatic difference reflects the difference in specific surface area. High-surface carbon black grades have specific surface areas of 200–1000+ m²/g, while most inorganic pigments are 5–30 m²/g. Far more dispersant molecules per unit mass are needed to adequately cover the available surface area of high-surface carbon black. The 40–80% figure correctly reflects this surface area requirement — it is not an unusually large addition when viewed relative to the surface area that needs to be stabilised.
Should DH-6200 be evaluated differently for solvent-free epoxy colour paste versus solventborne epoxy systems?
Yes — solvent-free epoxy colour paste operates at very high solid content with no solvent to moderate viscosity, making the wetting and viscosity-reducing role of the dispersant more critical. The optimal dosage for a solvent-free system may differ from a solventborne epoxy formulation. Evaluation at the actual solid content and resin viscosity of the specific solvent-free system, with viscosity and flow state as the primary performance indicators alongside fineness and storage stability, gives the most relevant result for that application.
