Select a pigment grade that reaches the required color and transparency or opacity within the ink’s processing and viscosity limits. In waterborne flexographic and gravure inks, that requires matching particle characteristics and surface treatment to the grinding vehicle, dispersant, and final binder. Compare grades first in a common formulation, then evaluate promising candidates at the required print color. A candidate that needs a different dispersant or pigment loading belongs in a reformulation trial. Approve the resulting ink only after its flow, color, and transfer remain acceptable through binder letdown, storage, and printing.

This guide addresses organic pigments and carbon black in aqueous acrylic-based inks. It provides a screening and interpretation framework; acceptance limits must come from the intended ink, substrate, and printing process.

Match Optical Requirements and Dispersion Behavior

Two grades with the same Color Index designation can differ in crystal form, particle characteristics, and surface modification. Those differences can affect both color development and dispersion behavior.

For organic pigments, define the required optical effect: a transparent process-color ink and a hiding spot-color ink have different priorities. Finer grades can support transparency and color development while creating a greater stabilization challenge. Initial opacity, transparency, or color strength can also reflect incomplete dispersion or flocculation. Establish a sufficiently dispersed, stable state before treating an optical mismatch as a reason to reject the grade. A grind-gauge result alone cannot establish that state.

A published study of organic pigments for inkjet applications links particle characteristics to optical performance and compares surface-treated and untreated Pigment Red 122 in aqueous dispersions. In its specific binder-free formulations, surface treatment improved resistance to particle-size and viscosity increases during storage with a glycol ether co-solvent. This supports evaluating surface treatment together with vehicle composition. Its formulation conditions and performance results cannot be transferred directly to flexographic or gravure inks.

Use milling progression, color development, and suitable particle-size or stability evidence together to assess dispersion. If optical performance remains unsuitable after adequate dispersion is established, screen another optical grade. If the optical target is achieved but stability fails, investigate the dispersant and surface treatment. A poor first grind establishes a problem with the tested combination, rather than a definitive optical limitation of the pigment.

For carbon black, compare aggregate structure as well as particle size and surface chemistry. Orion’s waterborne printing-ink guidance describes higher-structure grades that improve holdout on absorbent substrates, alongside lower-structure grades with less viscosity impact that permit higher pigment loading in suitable systems. A black selected for corrugated board therefore needs a different comparison from one selected for coated paper or film.

Separate a Direct Replacement from a Reformulation

Keep the comparison basis explicit so that changes in water, resin, or additive content are accounted for.

Screen a direct replacement in the existing formula

Replace the reference pigment on an equal dry-pigment-mass basis. Keep grinding resin, dispersant chemistry and active dosage, water quality, neutralizer, and letdown package unchanged.

Use a common milling procedure and record temperature, time, media conditions, and energy where available. Measure samples after the same cooling and conditioning period. Do not thin one candidate to match the reference viscosity during this comparison.

This establishes compatibility with the existing formula and process. Failure here rules out a straightforward replacement under those conditions; it does not establish that the grade is unusable.

For supplied pigment dispersions, account for their carrier resin, water, and additives. If their compositions cannot be balanced from available data, compare them as formulated concentrates and state that limitation.

Evaluate reformulated candidates at the required color

For promising grades, define the permitted changes before optimization. A useful starting design keeps binder identity and binder solids per unit mass of finished ink constant, adjusts pigment loading to reach the color target, and balances the formula with water. Carry the selected active-dispersant-to-pigment ratio through the calculation.

Record the resulting pigment content, total solids, binder-to-pigment ratio, and dispersant content. These quantities cannot all remain constant when pigment loading changes.

For the laboratory color comparison, verify dry ink mass per unit area using a method suited to the substrate and deposited amount. Use consistently conditioned samples and a defined comparable range. The same applicator setting does not establish equal dry deposits when solids and flow differ. If deposit cannot be verified, report the result as a comparison under fixed drawdown conditions, with that limitation.

At comparable dry deposits, the color result assesses the optimized formulations. It does not isolate the pigment’s contribution to viscosity or its intrinsic tinting strength. Film resistance also needs checking because the binder-to-pigment ratio has changed.

Decide Whether the Millbase Needs More Milling or a Different Dispersion System

A millbase must be wetted, mechanically deagglomerated, and stabilized. A dispersant cannot substitute for adequate milling exposure.

Take samples during milling and compare coarse material, color development, and viscosity after consistent conditioning. If coarse material decreases and useful color continues to develop, further milling may be justified within the equipment’s operating limits. If those results have plateaued while viscosity remains excessive, investigate the formulation and pigment grade before extending milling.

BYK’s practical guidance recommends optimizing dispersant dosage experimentally and considering alternative pigment surface treatments when grinding results are unsatisfactory. It also cautions that surface-area and oil-absorption calculations are not universally reliable dosage predictors.

Prepare fresh millbases across a supplier-supported dosage range. Express dosage as active dispersant relative to pigment mass, distinguish active content from total solids, and correct the carrier-water balance. The following patterns are screening interpretations, rather than proof of a molecular mechanism.

When changing dispersant chemistry, begin with a fresh grind. A failed post-addition correction is weak evidence for rejecting a combination that was never evaluated with the dispersant present during milling.

Locate Letdown Thickening Before Rejecting the Pigment

Letdown introduces the remaining binder and ingredients into the millbase. The surrounding liquid must remain compatible with the stabilizing layer on the pigment.

BYK’s explanation of steric stabilization describes two requirements: adsorption to the pigment and compatibility of the protruding polymer chains with the surrounding vehicle. Poor compatibility can reduce stabilization even when the initial grind was satisfactory.

Retain the original millbase and prepare the complete ink using the intended addition sequence. If abnormal thickening appears, investigate in the following order.

Check composition and measurement conditions

Confirm actual additions, sample mass, solids, temperature, conditioning, pH, and entrained air against the reference. Compare samples under the same shear history.

Document corrective adjustments and repeat color and stability measurements before attributing the result to the pigment.

Compare a pigment-free vehicle control

Prepare the corresponding grinding-vehicle and letdown blend without pigment, accounting for the liquid and additives carried by the millbase.

A similar thickening trend in the blank shows that vehicle behavior contributes to the problem. The blank has different particle interactions, so it cannot quantitatively separate resin and pigment contributions or exclude simultaneous pigment instability.

If the blank remains acceptable while the pigmented ink thickens and loses color or develops larger particles, pigment-related destabilization becomes a stronger working hypothesis.

Isolate the addition that changes the result

Where composition permits, compare controlled aliquots with the suspected letdown ingredient present and absent. Keep dilution, binder solids, and conditioning comparable, and record differences that cannot be matched.

For systems relying on electrostatic stabilization, electrolyte changes are relevant: ion concentration and ion valency can weaken the electrical double layer. Conductivity can flag a change, but it does not identify the ions or prove causation.

Treat improvements from a revised addition sequence or a supplier-supported pH adjustment as evidence of a controllable formulation dependency. They do not establish a specific adsorption mechanism.

Retain the pigment if the corrected formulation repeatedly meets requirements. Screen another dispersant or surface treatment when the optical grade is suitable but instability persists. Remove the candidate from this application’s shortlist when acceptable flow requires compromising color, solids, or film performance.

Connect Each Measurement to a Selection Decision

A grind gauge screens coarse material. A satisfactory reading does not establish the full particle-size distribution or long-term stability. If a distribution is needed, use a suitable method with documented sample preparation; dilution can change the state being measured.

For viscosity, record instrument geometry or spindle, speed or shear rate, temperature, conditioning, and reading time. Use a flow range and recovery measurement when the ink’s behavior changes with shear. An efflux-cup result can support routine control without describing every condition encountered during pumping and transfer.

Measure transparency or opacity alongside color coordinates or optical density where the optical target requires them.

Interpret the measurements together. Viscosity drift accompanied by color loss or particle-size growth supports investigating dispersion instability. Viscosity drift alone leaves vehicle behavior, concentration, and measurement conditions unresolved. Stable viscosity with unacceptable color also fails the selection task.

Confirm the Selected Grade Under Printing Conditions

Carry the shortlisted formulation through defined storage and a representative circulation or print trial. Keep sealed-storage results separate from open circulation, where evaporation and temperature can change the ink.

For the application comparison, keep substrate, anilox or gravure-cylinder specification, speed, and drying conditions fixed, with other relevant settings controlled. Record actual ink transfer or dry deposit where practicable. Equal press settings do not guarantee equal transfer: a color difference can reflect deposited quantity as well as the formulation’s optical response. Interpret this as performance under the selected print conditions.

Check color and flow as the ink circulates, recording water or neutralizer additions. A candidate requiring repeated correction has not demonstrated the same operating stability as a reference that stays within the agreed limits. If settings are changed to accommodate it, document the revised setup as an implementation requirement.

Select a grade only when its optical performance, dispersion window, binder compatibility, and printing behavior meet the defined application requirements.

ChemicalCell’s Pigments category can support initial material browsing. Confirm the exact grade, surface-treatment information where available, and aqueous application data before including a listed material in the comparison.