For aqueous acrylic flexographic and gravure inks, select carbon black together with its dispersant at the pigment loading needed to reach the specified printed blackness. Compare candidate formulations at a controlled dry ink deposit, then verify millbase processability, finished-ink viscosity and required film performance. A higher dispersant-to-pigment ratio can still give a lower active dispersant content in the finished ink if the required pigment loading falls sufficiently. Make that calculation using confirmed active content; assess viscosity by measurement. Neither pigment loading nor dispersant percentage alone establishes the better formulation.

This article serves formulators selecting pigmentary carbon black for aqueous acrylic-based flexographic and gravure inks on coated paper or suitably treated film. Inkjet, conductive inks and UV-curable systems require separate selection criteria.

Define the Blackness Target Before Comparing Grades

Specify the printed appearance that the ink must achieve. A solid black area, a transparent black layer and a grey made with white pigment are different optical tasks.

For a solid black, define lightness or a suitable jetness measure, undertone and any gloss requirement. Record optical density when it is part of print acceptance, specifying reflection or transmission measurement as appropriate. A supplier’s tint-strength value measures performance in a white reduction; it does not directly establish the appearance of the solid black print. Orion’s colorimetry guidance treats full-tone blackness and tinting strength separately and shows that measuring geometry and surface reflection affect blackness results. orioncarbons.com

Use the same substrate, backing, drying and conditioning procedure, instrument settings and specular-reflection setting throughout the comparison. Verify dry ink deposit where practicable. A darker print produced by a heavier deposit does not establish better color efficiency.

Set the acceptable optical range before optimization. Once that range is met, additional jetness has value only if the application needs it and the formulation can accommodate its consequences.

Separate Surface Area, Aggregate Structure and Surface Chemistry

Surface area indicates an optical opportunity and a dispersion burden

Smaller primary particles generally provide higher surface area per unit mass. Cabot’s printing-ink guide associates this with greater jetness potential, higher dispersion-energy requirements and higher viscosity. Interpret the viscosity tendency at comparable pigment concentration; it does not establish the ranking after formulations are adjusted to equal color.

Carbon black primary particles are fused into aggregates, which associate into agglomerates. Cabot’s morphology description distinguishes these levels. The practical dispersion task is to break down agglomerates and stabilize the dispersed aggregates. A catalogue primary-particle-size value therefore cannot serve as the acceptance limit for a millbase particle-size test.

If a higher-surface-area candidate develops insufficient color in the first grind, establish whether its dispersion has been adequately developed before rejecting its optical potential.

Structure creates a separate viscosity tradeoff

Aggregate structure describes how primary particles are joined into aggregates. Oil absorption number, often reported as OAN or DBP absorption, characterizes void space within and between packed aggregates. It is a useful comparative descriptor, rather than a measurement of water demand in the intended ink.

Higher structure generally increases viscosity, while lower structure can support lower viscosity and higher pigment loading. Cabot also identifies substrate-dependent selection: higher-structure blacks can improve surface holdout and optical density in aqueous flexographic newsinks on porous paper. That result should not be transferred directly to coated paper or film.

A useful shortlist therefore includes a structure contrast where available, rather than only moving toward progressively finer blacks.

Surface chemistry changes the suitable dispersion system

Oxidative surface treatment can improve wetting, dispersion and flow in suitable ink systems. Its benefit depends on the vehicle. An “oxidized” label alone cannot establish lower dispersant demand or compatibility with the final acrylic binder.

Request the exact grade’s surface-treatment information and aqueous application guidance. Record pH and neutralizer additions during trials instead of assuming that two carbon blacks will leave the vehicle unchanged. Orion’s aqueous-coatings guidance emphasizes pigment–dispersant–binder compatibility and appropriate pH adjustment; it provides relevant dispersion principles, without validating a particular printing-ink formulation. orioncarbons.com

Compare Dispersant Demand on Two Bases

Record active dispersant relative to dry carbon black and active dispersant per unit mass of finished ink. The first helps describe the pigment’s formulation requirement. The second captures the additive burden after pigment loading has been adjusted to achieve the target color.

If P is the dry-pigment mass fraction in the finished ink and d is the active-dispersant-to-pigment mass ratio, the finished-ink active dispersant mass fraction is P × d. Use decimal fractions in this calculation.

The following hypothetical calculation assumes that three formulations have independently met the same optical target at comparable dry deposits. The values illustrate accounting only; they are neither measured grade performance nor recommended dosages.

B saves pigment relative to A but uses more active dispersant. C uses less of both. Neither result predicts viscosity, storage stability or film resistance.

Keep commercial additive mass separate from active mass, and account for carrier water or solvent. ISO 3251:2019’s published abstract describes a mass-based determination of nonvolatile matter and explains that its result depends on heating temperature and duration, with effects such as solvent retention or loss of low-molecular-mass constituents. www.iso.org

For dosage accounting, the implication is that this residue measurement alone cannot identify the mass of the active dispersing component. Use a supplier-confirmed active-content basis for d. Active content and nonvolatile content may coincide for a particular product; confirm that equivalence before substituting one for the other. If only nonvolatile content is available, label the calculated addition as nonvolatile additive relative to dry pigment and retain that limitation until the active-content basis is confirmed.

This comparison prevents two premature decisions: rejecting a high-color grade solely because its dispersant percentage on pigment is higher, or approving it solely because its pigment loading is lower.

Find a Usable Grade–Dispersant Window

For each shortlisted grade, evaluate a small dosage series using a dispersant recommended for that pigment and aqueous vehicle. BYK advises experimental dosage optimization and cautions that calculations based on BET surface area or oil absorption are not generally reliable across pigment types. www.byk.com

Initially hold pigment concentration, grinding vehicle and milling procedure constant within each grade’s dosage series. Balance the additive carrier so that increasing dosage does not simply dilute the pigment. Record temperature and actual milling exposure, and sample after consistent conditioning.

Assess color development and dispersion evidence alongside viscosity. Before comparing developed color, check that further milling within the permitted process produces no color improvement beyond the established repeatability of the test, with acceptable coarse-material results. A viscosity minimum is a candidate operating point; confirm that the resulting dispersion remains acceptable after letdown and storage. Prefer a repeatable working range to an isolated best result.

Compare promising combinations at the required printed color. Define the permitted reformulation first: for example, retain binder identity and finished-ink binder solids, adjust pigment loading and balance water. Record the resulting total solids, binder-to-pigment ratio and active dispersant content. These quantities cannot all remain constant as pigment loading changes.

If one candidate requires different dispersant chemistry, identify it as a formulation alternative. Its performance does not demonstrate a direct replacement in the existing recipe. ChemicalCell’s broader waterborne-ink pigment selection guide explains that distinction and the investigation of letdown thickening.

Keep Millbase Processability Separate from Finished-Ink Flow

A concentrated black millbase must operate within the mill’s usable viscosity range. Excessive viscosity can restrict grinding-media movement and increase heat generation. Orion’s dispersion guide discusses these processing limits; diluting every candidate to the lowest possible viscosity is therefore an unsuitable universal optimization target. orioncarbons.com

Evaluate finished inks separately at matched temperature and conditioning. Record instrument geometry or spindle, shear rate or speed, and measurement timing. Where relevant, include low-shear behavior, flow under application-related shear and recovery after shear. Compare the results with an acceptable production reference using the same method.

If a candidate reaches the blackness target but exceeds the finished-ink viscosity limit, first confirm adequate dispersion and the selected dosage window. Then compare a lower-structure grade or another surface-chemistry/dispersant combination. If the formula needs added water, include the changed solids, transfer and drying behavior in the assessment.

Extra water is a formulation change with application consequences. It cannot, by itself, demonstrate that the original jetness–viscosity tradeoff has been resolved.

Select the Combination That Preserves the Printed Result

For the final comparison, carry each optimized formulation through the same defined storage and representative print or circulation conditions. Record corrections and verify blackness, undertone, transfer, drying, adhesion and rub or water resistance where required by the application. Keep sealed-storage results separate from open-circulation behavior.

Choose a higher-surface-area grade when its optical benefit survives dispersion, letdown and printing at acceptable additive demand and rheology. Choose a lower-structure alternative when it provides the required color with a more workable viscosity range. Retain a less demanding optical grade when it already meets the print specification and further blackness creates an unnecessary formulation burden.

ChemicalCell’s Pigments category provides a starting point for material browsing. For the next formulation comparison, confirm grade-specific surface-area and oil-absorption data with their methods, surface-treatment information and relevant aqueous application evidence, together with the proposed dispersant’s active-content basis. Approve the combination on its measured performance at the required printed color.